Earlier this week, I found myself dissecting an embargoed briefing video frame by frame, like a JFK obsessive trying to squeeze meaning from the Zapruder film. I鈥檇 just had an interview with three top scientists from Nike鈥檚 Breaking4 team, the group tasked with coordinating Faith Kipyegon鈥檚 attempt to run the first women鈥檚 sub-four-minute mile later this month. I got some answers, but I still had some big questions, and I hoped the video might reveal some clues.

Ever since back in April, there鈥檚 been speculation about how Kipyegon will be able to make the leap from her current world-record time of 4:07.64 to sub-four. It鈥檚 reminiscent of the uncertainty that surrounded the company鈥檚 Breaking2 project in 2017, when they announced that Eliud Kipchoge and two other runners would aim for a sub-two-hour marathon at a time when the world record was 2:02:57. Such a big leap鈥�2.4 percent, compared to the 3.1 percent Kipyegon needs鈥攕eemed implausible, and most observers dismissed the announcement as an overhyped publicity stunt. Then Kipchoge ran 2:00:25 (and later broke 2:00 in another exhibition race). So the commentary this time has been more circumspect. Nike must have something up their sleeve, the thinking goes, otherwise they wouldn鈥檛 be sticking their necks out.

The three experts Nike made available to discuss the project were Carrie Dimoff from the Innovation Footwear team, Lisa Gibson from the Apparel Innovation team, and Brett Kirby, a physiologist at the Nike Sport Research Lab. The choice of experts tells us which levers the company hopes to pull in pursuit of a four-minute mile. Here鈥檚 what they revealed.

The Shoes

The least surprising news is that Kipyegon will be wearing bespoke racing shoes, dubbed the Victory Elite FK, designed to make her faster than she was in the Victory 2 spikes she set her current record in. How much faster the new shoes will be is hard to determine, though.

When Kipchoge ran Breaking2, he did so in a radical new shoe design featuring a curved carbon fiber plate and a thick layer of ultra-resilient midsole foam. Those shoes came with a lab-tested promise: they made runners four percent more efficient, on average. That kind of efficiency difference is capable of reducing race times by two to three percent. In other words, the shoes alone made Breaking2 plausible.

Quantifying the benefits of Kipyegon鈥檚 new spikes is harder for a couple of reasons. One is that you can only measure efficiency accurately when you鈥檙e running slower than your aerobic threshold. At faster speeds, like your mile race pace, you start relying on 鈥渁naerobic鈥� metabolism, which 诲辞别蝉苍鈥檛 require oxygen. Since running economy is calculated based on how much oxygen you鈥檙e consuming, our go-to measurement techniques are no longer accurate once you go anaerobic.

Even if it was possible to measure running economy at mile speed鈥攊f we knew that, say, the new spikes were 4 percent more efficient than previous models鈥攖hat wouldn鈥檛 tell us exactly how much faster Kipyegon could run. For marathons, efficiency is crucial, because in a long race you鈥檙e inevitably going to run low on fuel. In a mile, you don鈥檛 have enough time to empty the tank. Efficiency is still useful, but it鈥檚 not the race-defining factor is it in longer events.

For sprinters, fuel efficiency is basically irrelevant. Instead, they鈥檙e concerned with how effectively they can transmit force to the ground to propel themselves forward, energy costs be damned. Milers are somewhere in the middle, needing to find a balance between efficiency and force transmission. The data Dimoff and her team collected on Kipyegon鈥檚 various shoe prototypes used a force-sensing treadmill to figure out how much power she could transmit to the ground, as well as biomechanical analysis to estimate how much energy she was burning. They didn鈥檛 share any numbers, but they saw measurable improvement in those parameters as they fine-tuned successive iterations of the new Victory Elite FK design.

More generally, there鈥檚 not a lot of data on the new generation of superspikes, which, like the road-running supershoes introduced in Breaking2, tend to have a midsole unit with lightweight, resilient foam, often alongside a stiff carbon fiber plate. The best info we have on such spikes comes from Wouter Hoogkamer and his colleagues at the University Massachusetts, Amherst鈥檚 Integrative Locomotion Lab. They that runners tended to go about 2 percent faster in superspikes than in conventional spikes.

An interesting detail in Hoogkamer鈥檚 data is that men ran faster in spikes that had a carbon plate in addition to the foam midsole. For women, on the other hand, the carbon plate didn鈥檛 make any difference. That suggests that the generic plate used in the test shoes might have been too stiff for the women to exert enough force to take advantage of its propulsive properties. If that鈥檚 true, then the extensive fine-tuning that Nike is doing to create a shoe specifically tailored to Kipyegon鈥檚 stride has the potential to make her faster than an off-the-shelf shoe.

With that preamble, what does Kipyegon鈥檚 new shoe look like? In some ways, it鈥檚 a lot like the that she wore last year. It has an air pod (a bubble designed to compress and then spring back to return energy) under the forefoot, a wedge of ZoomX foam under the heel, and a curved carbon fiber plate running under the length of the sole. They鈥檝e pulled out all the stops to use thinner and lighter materials for the upper, and the spikes themselves鈥攕ix rather than the four in the Victory 2鈥攁re 3D-printed titanium to reduce weight. One of the prototypes they tested was a barely-there 83 grams, compared to a listed weight of 136 grams for the Victory 2. Based on the rule of thumb that every hundred grams of shoe weight burns an extra one percent of energy, that’s half-percent edge in weight alone. Thanks to all this trimming, the Nike team has been able to make the forefoot air pod three millimeters thicker, which gives a little more energy return over the Victory 2. According to Dimoff, the air pods return more than 90 percent of the energy you put into a given foot strike.

World Athletics rules limit the stack height (i.e. the total thickness of the sole) of track spikes to 20 millimeters. Dimoff said the shoe will conform to this and other requirements. In fact, in Kipyegon鈥檚 sole track outing of the year so far, a 1,000-meter race in 2:29.21 at the Xiamen Diamond League race in April, she wore a version of the new shoe which had gone through the World Athletics approval process (I鈥檓 pretty sure it鈥檚 the Dev 611 shoe listed ). That certification process takes about 30 days; since Dimoff鈥檚 team wants to continue making tweaks right up to the last minute, they won鈥檛 be submitting the Breaking4 shoe for certification, but expect that it would pass if submitted. That, on its own, is enough to guarantee that whatever time Kipyegon runs won’t count as a world record, whatever other rules they do or don’t bend.

The Apparel

There鈥檚 lots to say about the 鈥淔ly Suit鈥� Nike is designing for Kipyegon, but I鈥檓 probably not the right person to say it. A lot of the focus for Gibson鈥檚 team is making sure that Kipyegon feels good鈥攃omfortable, confident, unconstricted鈥攚hile she runs. I鈥檓 a big believer that these factors are important, but they鈥檙e very hard to quantify.

Of course, the team did do a ton of aerodynamic testing, both in the wind tunnel and with simulations. The fabric has 3D-printed Aeronodes: little bumps of varying size distributed across the garment to create mico-eddies that reduce the turbulence of the air flowing past Kipyegon. The suit comes with arm sleeves with articulated elbows to minimize creasing, which also extend forward to cover the knuckles, where some of the most turbulent air can be found. It鈥檚 got a headband, the running equivalent of an aero helmet in cycling. Nike is also debuting a special new sports bra that鈥檚 3D-printed out of ultralight TPU, a polymer that鈥檚 better known to runners as one of the midsole foam materials used in supershoes.

How much does this stuff matter when you put it all together? Presumably Nike has a wind tunnel estimate comparing runners鈥� energy consumption with the new suit compared to business-as-usual, but the researchers didn鈥檛 share it. For Breaking2 in 2017, one of Nike鈥檚 apparel specialists told me they figured they would get somewhere between a second and a minute over the course of the marathon from all the aerodynamics they鈥檇 worked on鈥攁nd that this was crucial, because if Kipchoge missed the two-hour barrier by a second, they would never forgive themselves. Gibson told me something similar about the Breaking4 suit: 鈥淲e didn鈥檛 want to leave anything on the table.鈥�

Everything Else鈥ncluding Drafting

Adding up the hypothetical numbers for the shoes and clothing, a four-minute mile still seems far away. I was imagining some pretty far-out scenarios when Nike first announced this attempt, like a specially built track with perfect bounciness and optimized curves, but Kirby shot those ideas down quickly. The race is going to take place at Stade Charl茅ty in Paris sometime between June 26 (the most likely date) and June 28. They鈥檙e not building anything new or modifying the stadium or track surface in any way. They chose it because, based on a review of decades of environmental data, it鈥檚 likely to have great weather and in particular a low likelihood of storms. It also helps that Kipyegon has set a couple of world records in that stadium: 5,000 meters in 2023, 1,500 meters in 2024.

I asked about nutrition and supplements. For example, Kipyegon has reportedly tried baking soda in at least some of her prior races. Kipyegon has her own nutrition team through her sports management agency, according to Kirby, so Nike isn鈥檛 making any changes to the regime she鈥檚 already on. They are, however, monitoring and analyzing her training. What sort of insights does that provide? Kipyegon is strongest over the 1,500 to 5,000-meter range rather than over shorter distances like the 800 meters, Kirby noted, so the training analysis indicated that she needs to develop her speed鈥攐r, as physiologists would say, her anaerobic capacity. Kipyegon鈥檚 legendary coach, Patrick Sang, probably didn鈥檛 need a supercomputer to uncover this insight, but perhaps the analysis is helping him figure out just how much speedwork is enough, and how he can add it in without compromising her endurance.

That leaves drafting. After Breaking2, most of the post-mortems attributed Kipchoge鈥檚 big leap in performance to some mix of supershoes and the pacers who surrounded him and blocked the wind for almost the entire race. Some thought his success was virtually all pacers; others thought it was virtually all shoes, and that debate continues to this day. Breaking4 will give us another datapoint. In this case, the shoes don鈥檛 seem like a radical break with the shoes Kipyegon and others have already been wearing, so it seems to me they must be relying on drafting. Some recent research from Rodger Kram鈥檚 group at the University of Colorado, completely unconnected to the Breaking4 initiative, suggested that drafting alone would indeed be enough to get Kipyegon to sub-four.

How will they do it? Nike鈥檚 official line is that they haven鈥檛 decided yet. How many pacers will there be? TBD. In what formation? TBD. Will they be men or women? TBD. Will they run the whole race or, as in Breaking2, sub in and out partway? TBD. Will there be pacers at all, or might she just run a solo time trial guided by nothing but pace lights? TBD. I can believe that they鈥檙e still fine-tuning the details, but I have a hard time believing all those options are still on the whiteboard.

That鈥檚 where the frame-by-frame video analysis comes in: In one of Nike鈥檚 briefing videos about the science, in the background at what appears to be the forest-shrouded track on Nike鈥檚 main campus, you can see glimpses of what looks like drafting experiments going on. A runner clad in white circles the track with something鈥攑erhaps an air pressure or wind sensor?鈥攕trapped to their chest. Sometimes they鈥檙e alone; sometimes there are two other runners in black singlets directly and diagonally in front of them; sometimes there are three. In one shot, five pacers form a half-diamond in front, beside, and behind the central runner.

Which configuration will it be? Who knows. My best guess, triangulating between physiology and optics, would be either one shift of five men taking her all the way to the finish, or two to three shifts of five women taking turns. But I can鈥檛 blame the Nike team for not spilling all the details in advance. I would probably do the same in their shoes. However you add up the numbers, getting to sub-four is going to require a stupendously, perhaps even magically, good day. On his best days, Eliud Kipchoge seemed to be able to summon some magic from a deep well-spring of self-belief that transcended all the shoe tech and pacers and hyper-optimized conditions. Nike is clearly hoping that Kipyegon will be able to do the same. But the thing about magic is that, if you talk about it too much, it tends to disappear.

Faith Kipyegon鈥檚 Breaking4 race is scheduled for the evening of June 26. I鈥檒l be providing on-the-ground coverage from Paris before, during, and after the race, so stay tuned.

For more Sweat Science, join me on and , sign up for the , and check out my new book .

The post Nike and Faith Kipyegon Plan to Crack the Four-Minute Mile This Month. Here’s How. appeared first on 国产吃瓜黑料 Online.

Nearly of Americans struggle with back pain, making it the most common area of the body for aches. While it鈥檚 tempting to quit all activity and recuperate in bed with a heating pad, some doctors recommend a different approach for finding relief from back pain: hiking.

If your back is throbbing, you probably won鈥檛 feel like doing much of anything, let alone hitting the trails. However, going for a hike during your recovery period and beyond can help accelerate the healing process and even reduce the risk of future issues, according to doctors I interviewed.

I struggled with back pain for years and made the mistake of cutting back on my usual hikes after flare-ups. But my doctor suggested moving more to help reduce pain, along with other lifestyle hacks, and the results have been impressive. I haven鈥檛 experienced a major back pain episode in five years.

Back issues are personal, and experts say it鈥檚 important to be strategic about using hiking to ease your pain. Here鈥檚 what they recommend.

How Hiking Can Help Get Rid of Back Pain

A considerable body of research supports听walking as a treatment for back pain. A 2024 study published in followed more than 700 adults over a three-year period who had recently experienced lower back pain. Half were assigned to a walking program, with a goal of walking 30 minutes each day, five days a week, while the other half received no intervention, but were allowed to seek outside treatment if they experienced any new back pain during the study. (Researchers believed this to be the most realistic comparison to the group that received the walking intervention.)

The researchers found that individuals in the walking group experienced fewer recurrences of back pain and had longer intervals between back pain episodes compared to those who received no intervention. The differences were striking: people in the walking group had approximately 208 days between back pain episodes, whereas those who made no change to their typical recovery regime typically experienced pain again after 112 days.

A 2020 analysis of existing research published in the found that regular exercise, which can include activities such as hiking and walking, is an effective way to prevent recurring back pain. A 2019 systematic review published in the journal also found that physically active people had the lowest risk of back pain.

That said, most of these studies used sidewalk excursions and treadmill walks as their experimental focus, and walking on a flat road is very different from hiking. Walking of any kind helps to activate the muscles around the spine, which can help to reduce pain for many people, says , a physician specializing in interventional pain medicine. 鈥淚n my personal opinion, hiking is even better,鈥� he says.

Hiking involves walking on uneven ground, which engages more muscles in the back, including small stabilizers, glutes, and the core, to keep you upright, Kennedy says. Activating your lower back muscles also engages the core, thus strengthening it, and a stronger core stabilizes the spine.听A weak core, on the other hand, increases the risk of spinal misalignment, leading to more pain, he adds.

, associate professor of exercise and nutrition sciences at the George Washington University Milken Institute School of Public Health, says that hiking can also improve听balance and your body鈥檚 ability to sense its own movements. This can help reduce compensatory movement patterns听like . If left unchecked, compensatory movement patterns can lead to even more pain in the future by throwing your alignment out of whack, Miller says.

Going up and down hills during hikes can also be helpful. 鈥淯phill hiking challenges postural muscles鈥攊ncluding the 鈥攅ncouraging a more upright posture while engaging the glutes, hamstrings, and core to reduce excessive spinal loading,鈥� Miller says. 鈥淐onversely, downhill hiking requires controlled eccentric movement, forcing the body to absorb impact gradually, which strengthens the legs and minimizes spinal strain.鈥�

One more thing to consider, according to Miller, is that hiking immerses you in nature, which has been linked to . 鈥淭hat calming, stress-relieving effect can reduce the perception of pain by decreasing overall muscle tension,鈥� he says.

What Is the Best Way to Hike to Relieve Back Pain?

If you鈥檙e in the thick of a back pain flare, Kennedy says it鈥檚 best to wait for the pain to subside a bit before starting your hiking routine. 鈥淥nce your flare has resolved, staying active and doing core-type exercises, including hiking, helps to reduce recurrent pain,鈥� he adds.

You don鈥檛 need to be entirely pain-free to go on a hike, though. 鈥淎 little pain while you鈥檙e doing something is OK as long as when you stop, you go back to your baseline and the pain 诲辞别蝉苍鈥檛 flare up,鈥� Kennedy says. 鈥淚 don鈥檛 want people to go for a mile hike and then be laid up for three days. But if you can hike, have a little discomfort, and don’t need to lie down for the rest of the day, great.鈥�

Wear the Proper Footwear, Stretch, and Monitor Your Posture

For footwear, it鈥檚 important to have a deep tread to get a solid grip on uneven surfaces, says , a podiatrist at Heartland Foot and Ankle Associates in Bloomington, Illinois. She suggests investing in shoes with a low heel, between 1/2 inch and 1 inch鈥攈er favorites are . 鈥淭hat will give the muscles in the back of the leg a little bit of an advantage and realign the hip bones, which will ultimately help the lower back,鈥� she says.

, an orthopedic spine surgeon and director of the Cedars-Sinai Spine Center in Los Angeles, recommends stretching your glutes and hamstrings before going on a hike. Then, move at a pace that feels comfortable to you.

Pay attention to your posture when you walk: that means trying to keep your head stacked over your neck, with your shoulders back (not hunched over), Kennedy says. 鈥淧osture matters.鈥�

How Long Should You Hike to Get Relief from Back Pain?

A lot depends on your baseline fitness level, as well as how comfortable you feel, according to Miller. 鈥淪tart with 30 to 45 minutes on mild terrain, then gradually increase time and difficulty,鈥� he says. 鈥淭he key is consistency rather than pushing for long distances right away.鈥�

If you find that amount of time is comfortable for you, Miller says you can ramp up hike time to 60 or 90 minutes 鈥渁s long as you maintain proper form and don鈥檛 experience flare-ups.鈥�

Through all of this, it鈥檚 crucial to listen to your body. Suppose you鈥檙e hiking and you experience pain. In that case,听it’s best to back off, says , a board-certified spinal surgeon at at Mercy Medical Center in Baltimore. That might mean slowing down your pace, looking for a flatter surface, or scaling back on the length of your hike and then gradually building it up again, she says.

But Miller 诲辞别蝉苍鈥檛 recommend that you stop hiking right away unless you鈥檙e dealing with significant pain. 鈥淚t often takes several sessions for the body to adapt to the movement demands and for the benefits to become noticeable,鈥� he says. That鈥檚 why he suggests hiking two to three times a week for three to four weeks before deciding if it鈥檚 right for you. 鈥淚f pain worsens, consider evaluating factors such as posture, footwear, pack weight, and intensity rather than quitting outright,鈥� he says.

The Best Way to Hike Up and Down Hills When Your Back Hurts

Your hiking form can play a big role in your comfort level, especially if you have upper or lower back pain, according to Miller. However, your posture may vary slightly when walking uphill and downhill, as well as depending on whether you experience upper or lower back pain.

How to Hike Uphill and Downhill When You Have Lower Back Pain

Miller says there鈥檚 a specific posture to consider when you have low back pain. 鈥淲hen hiking uphill, it鈥檚 important to engage the glutes and core while avoiding excessive arching of the back,鈥� Miller says. 鈥淯sing a short, steady stride rather than long steps can reduce spinal stress and improve stability.鈥�

When you head downhill, Miller suggests keeping a slight bend in the knees to absorb impact and keep jarring forces from traveling up your spine. 鈥淯sing trekking poles can also help offload pressure from the lower back, providing additional support,鈥� he says.

How to Hike Uphill and Downhill When You Have Upper Back Pain

If upper back pain is your issue, Miller suggests keeping your shoulders relaxed and avoiding hunching forward when going uphill. Otherwise, you run the risk of increasing tension in your upper back, which can lead to more pain, he says.

鈥淲hen descending, focusing on controlled movements and avoiding excessive slouching or rounding of the shoulders can help prevent discomfort and maintain proper spinal alignment,鈥� Miller says.听It can help to think of pinning your shoulder blades down and back while you hike, and engaging your core to keep your spine upright.

Make Sure Your Hiking Pack Isn’t Too Heavy

Your pack is important for carrying the essentials, but Miller says it鈥檚 crucial to wear it properly, especially when you have back pain. He recommends keeping your pack weight to ten pounds or less and trying to distribute the contents’ weight evenly.

鈥淎 well-fitted backpack with hip and chest straps [] can help offload pressure from the spine, reducing strain and promoting better posture,鈥� he says.

Miller also suggests placing heavier items closer to the pack鈥檚 center for improved weight distribution. (If you鈥檙e new to hiking, Miller suggests starting with no pack, if you can, to allow your body to adjust to the movement without extra strain.)

Doctors agree that a hiking habit can be a great way to lower the risk of future back pain flares. 鈥淭he most important thing for back pain is that you move,鈥� Kennedy says. 鈥淚f you can get out in nature and hike, that鈥檚 even more of a win.鈥�

The post How Hiking Can Help Relieve Upper and Lower Back Pain appeared first on 国产吃瓜黑料 Online.

If I told you that NASA has developed a radical new way of monitoring and quantifying your workouts, and that that method outperforms all others, you鈥檇 probably assume that it involves bleeding-edge science. There would be AI, and some sort of wearable or perhaps even injectable technology. It would be very expensive.

But you鈥檇 be wrong, for reasons that tell us something important about the quest to transform training optimization from an art into a science. A new study by Mattia D鈥橝lleva and his colleagues at the University of Udine compares different ways of assessing the 鈥渢raining load鈥� of different workouts鈥攁nd finds that a low-tech NASA questionnaire produces the most accurate results. The findings offer a reminder that outsourcing our training decisions to wearable tech algorithms 诲辞别蝉苍鈥檛 always outperform simply listening to our bodies. The research also raises a tricky question: is the workout that makes you most tired also the one that increases your fitness the most?

Why Does Training Load Matter?

The goal of training is to impose a stress鈥攁 training load鈥攐n your body that makes it tired in the short term but triggers adaptations that make it fitter in the long term. Going all-out in one workout isn鈥檛 constructive, even though it imposes a huge training load, because it leaves you too tired to train effectively the next day. The art of training is figuring out what mix of easy, medium, and hard workouts will enable you to accumulate the greatest possible training load over weeks and months without getting crippled by fatigue.

In its simplest form (as I discussed here), the training load of a workout is a combination of how hard you push and how long you push for. But the details get tricky. What鈥檚 the best measure for how hard you鈥檙e pushing? You could use pace, power, heart rate, heart rate variability, lactate levels, perceived effort, or other progressively more esoteric metrics. And how do you combine effort with duration? You can鈥檛 just multiply them together, because effort is nonlinear: running twice as fast for half the distance won鈥檛 produce the same training effect.

The , which is published in the International Journal of Sports Physiology and Performance, compares seven different ways of calculating training load. Four of them are variations on a concept known as TRIMP, which is short for 鈥渢raining impulse鈥� and is based on heart rate measurements, using equations that account for lactate levels, breathing thresholds, and other details. A fifth uses heart-rate variability, and a sixth uses a subjective rating of effort. (Most fitness wearables, by the way, likely use a combination of the above methods, though their exact algorithms are typically proprietary.) The seventh method is the NASA questionnaire, which we鈥檒l come back to.

The gold standard against which all these methods were compared is the 鈥渁cute performance decrement,鈥� or APD. Basically, you do an all-out time trial, then you do your workout, then you do another all-out time trial. Your APD is how much slower the second time-trial is compared to the first one, as a measure of how much the workout took out of you. Obviously this isn鈥檛 a practical way of monitoring training, because you can鈥檛 race before and after every workout. But for researchers, it鈥檚 a way of checking whether various methods鈥攊ncluding the seven they tested in this study鈥� correspond to the reality of how hard a workout is on your body. At the end, they were able to figure out which method was the most reliable predictor of training load.

What the New Study Found

D鈥橝lleva and his colleagues recruited 12 well-trained runners (10 men and 2 women) to test four different running workouts on different days:

• Low-intensity training (LIT): 60 minutes at a pre-determined comfortable pace
• Medium intensity (MIT): 2 x 12:00 at a moderate pace with 4:00 easy recovery
• Long high-intensity (HITlong): 5 x 3:00 hard with 2:00 recovery
• Short high-intensity (HITshort): two sets of 11 x 30 seconds hard, 30 seconds easy

The performance test was running at VO2 max pace until exhaustion. When they were fresh, the runners lasted just under six minutes on average. After the one-hour easy run, their APD was 20.7 percent, meaning they gave up 20.7 percent earlier in the post-workout VO2 max run. After the medium-intensity run, the APD was 30.6 percent; after the long intervals, it was 35.9 percent; after the short intervals, it was 29.8 percent.

So how well were each of the seven training load calculations able to predict this APD? The short answer is: not very well. Here鈥檚 a comparison of APD (on the left) and one of the parameters studied, which is called bTRIMP and is based on heart-rate measurements and lactate curves:

In fact, the relationships are completely reversed: the easiest workout according to bTRIMP produces the biggest APD in reality, and the workout ranked hardest by bTRIMP produces the smallest APD. All except two of the training load calculations the researchers measured have similar upside-down relationships. The two exceptions are heart-rate variability and the NASA questionnaire, which look like this:

The heart-rate variability measures, on the left, don鈥檛 tell us much, because they鈥檙e basically the same after each of the four workouts. (You can see some subtle differences, but they鈥檙e not statistically significant.) The NASA questionnaire, on the other hand, bears a striking resemblance to the APD data, and the statistical analysis confirms that it鈥檚 a good predictor. In other words, it鈥檚 the only one of the seven calculations tested that, according to this study, accurately reflects how exhausted you are after a workout.

So what is this questionnaire? It鈥檚 called the , or NASA-TLX, and was developed in the 1980s. It鈥檚 simply a set of six questions that ask you to rate the mental demand, physical demand, temporal demand (how rushed were you?), performance (how well did you do?), effort, and frustration of a task. You answer each of these questions on a scale of 1 to 100, then the six scores are averaged鈥攁nd presto, you have a better measure of how hard your workout was than your watch or heart-rate monitor can provide.

What the NASA Questionnaire Misses

These results don鈥檛 mean that we should all start recording NASA-TLX scores in our training logs. Questions like how hurried you felt don鈥檛 seem very relevant to running, or to training in general. What鈥檚 more significant about the questionnaire is what it 诲辞别蝉苍鈥檛 include: any measure of how long the workout was.

All the other training load measures rely on a combination of intensity and duration. But the effect of duration swamps the measurement: that鈥檚 why the bTRIMP graph above shows the 60-minute easy run (LIT) as the workout with the biggest training load. It鈥檚 really just telling us that it was the longest workout. The NASA-TLX, on the other hand, just asks (in various ways) how hard the workout felt once it was done. That turns out to be a better way of predicting how much slower you鈥檒l be after the workout.

There鈥檚 an implicit assumption in all of this discussion, though, which is that the workout that provides the biggest training load is the one that will improve your fitness the most. Is APD鈥攈ow much slower you get over the course of a single workout鈥攔eally the best predictor of fitness gains? It鈥檚 easy to come up with scenarios where that鈥檚 not true. If I sprain my ankle, my APD will be enormous, but that 诲辞别蝉苍鈥檛 mean I鈥檓 going to be an Olympic champion next month. Similarly, you can imagine workouts that would inflict a disproportionate amount of performance-sapping fatigue鈥攕teep downhill running, for example鈥攃ompared to their fitness benefits.

Perhaps what we鈥檙e seeing here is not so much 鈥済ood鈥� (NASA-TLX) and 鈥渂ad鈥� (TRIMP) measures of training load, but rather good measurements for two different types of training load. The APD and NASA-TLX mostly reflect how hard/intense/fast the workout was. TRIMPs and other metrics that incorporate duration end up mostly reflecting how long the workout was. There鈥檚 no reason to assume that these two parameters are interchangeable. It鈥檚 not just that you can鈥檛 get the same training benefit by going twice as fast for half as long. It鈥檚 that there鈥檚 no equation that makes fast running produce the same benefits as slow running. They鈥檙e two different physiological stimuli, and the smart money says you need both to maximize your performance.

So where does this leave us? I鈥檓 not anti-data, and I鈥檓 open to the idea that some of the newer metrics provided by wearable tech might reveal useful patterns if you collect them consistently. But if you strip training down to its bare essentials, these results suggest to me that there are two separate parameters that really matter: how long and how hard. And for now, I鈥檓 not convinced that we have any measuring tools that are significantly better than a stopwatch and an honest answer to the question 鈥淗ow did that feel?鈥�

For more Sweat Science, join me on and , sign up for the , and check out my new book .

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Sometimes, the simplest movements can have the most profound impact on your body. Such is the case with , a stretch currently trending on TikTok that invites you to counter the hunching effects of contemporary life with an infant-inspired position.

Adult tummy time involves lying on your stomach, with your torso propped up by flat forearms (ironically, and conveniently, an ideal posture for typing and scrolling). A quick scroll through TikTok reveals many users pausing in the pose for a few breaths before lowering down; others are seen with their stomachs draped over pillows to alleviate back pain. The majority of sharers insist that the practice is the key to better posture.

Along with the minimal effort required to access tummy time, , a physical therapist and strength conditioning specialist in Los Angeles, says that the foundational position requires no equipment and can aid in breathing, spinal health, and, yes, improved posture.

The Benefits of Adult Tummy Time

Tummy time offers a direct contrast to the shape that many of us take throughout the day鈥攁ka hunched over screens and steering wheels.

According to , prolonged smartphone and screen time use听can directly affect the cervical and thoracic spine, resulting in postural compensations and muscle fatigue, commonly referred to as听tech neck. This condition is characterized by chronic neck or shoulder pain caused by a consistently rounded upper body posture.

While spending less time on your devices is an obvious solution, tummy time can provide additional and accessible relief.

鈥淲hen an adult gets into a prone (face-down) position, we鈥檙e encouraging spinal extension, the opposite of the forward-flexed posture most people fall into during screen time,鈥� says Glisic. Though for most adults this is largely a passive position, a lot is actually happening while you鈥檙e chilling on your belly. According to Glisic, tummy time activates the deep neck extensors, thoracic spine extensors, scapular stabilizers (including the lower trapezius and serratus anterior), and the deep core, promoting engagement that encourages spinal alignment.

Glisic adds that the pose also takes the pressure off areas that may be overworked for those who spend their days sitting, giving your pecs, hip flexors, and neck flexors鈥攁ll of which become tight in prolonged sitting鈥攁 welcome break.

Additionally, time spent lying on your belly and undoing daily stress patterns can increase body awareness, as it can be challenging to understand and address what鈥檚 happening in the body until you unpack these habitual patterns. With the addition of an open chest and diaphragm creating smoother, deeper breathing patterns, tummy time becomes a solution to more than one everyday ailment.

Adult Tummy Time Tips

Tummy time is a pose you can drop into whenever you need a spine-lengthening stretch.

Glisic recommends enjoying the posture as a reset, either pre- or post-workout, or as a standalone for 3-5 minutes a day, increasing the time range if it feels comfortable in your body.

If you experience lower back pain while on your stomach, elevating the body atop a pillow, bolster, or stability ball can help reduce strain. Additionally, be sure to place your feet at hip-width distance or even wider to minimize strain in the lumbar region.

Once you鈥檙e comfortable in the pose, Glisic suggests building in movement-based variations, such as arm lifts, head nods, or subtle backbends.

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Back in 1969, naval researchers took blood samples from the crew of a Polaris nuclear submarine over the course of an eight-week patrol. Three-quarters of the sailors were smokers, so carbon monoxide levels were chronically elevated in the sealed confines of the sub. After a few weeks in this toxic miasma, the crew鈥檚 levels of hemoglobin, the crucial protein in red blood cells that ferries oxygen from the lungs to the muscles, had shot up by an average of 4.4 percent. Secondhand smoke had somehow turned the submariners into aerobic superstars.

This finding, along with others like it, was filed away for decades. After all, smoking destroys your lungs, so any performance benefits are outweighed by the harms. But then, last year, the idea exploded. Scientists published fresh data showing that huffing carbon monoxide could boost endurance. Other scientists responded with editorials warning against fooling around with a gas whose nickname is 鈥渢he silent killer.鈥� And headlines around the world trumpeted the news that 鈥攃onfirmation, seemingly, of the clich茅 that elite athletes will accept any risk in exchange for victory. The full story, though, is a bit more complicated.

The quest for endurance is, in part, about hemoglobin. More hemoglobin means more oxygen delivered to your muscles, which means you can run or ride or swim faster, for longer. Starve your muscles of oxygen in training and your body responds by secreting EPO, a hormone that stimulates the production of hemoglobin-carrying red blood cells. That鈥檚 how altitude training works: There鈥檚 less oxygen available, so your body produces more EPO to compensate. (It鈥檚 also why synthetic EPO is the banned drug of choice among endurance athletes.)

Virtually all performance-enhancing drugs are associated with health risks, and that hasn鈥檛 harmed their popularity.

When you inhale carbon monoxide, some of your red blood cells ferry molecules of it (instead of oxygen) around your body. Carbon monoxide attaches to hemoglobin and 诲辞别蝉苍鈥檛 let go, making those red blood cells unavailable to carry oxygen for many hours. It鈥檚 like altitude training in a bottle: Your body will sense the oxygen shortage and respond by producing EPO. But inhale too much and you won鈥檛 deliver sufficient oxygen to your heart and brain鈥攁nd once your hemoglobin is clogged with carbon monoxide, it鈥檚 not easy to reverse. Around 1,200 people die every year in the United States from deliberate or accidental carbon monoxide poisoning.

So carbon monoxide as a performance booster has been understood but mostly unspoken. It wasn鈥檛 until 2018 that the idea got more concrete. An initial study confirmed that deliberately breathing carbon monoxide boosted EPO. The next year, researchers in China, tasked with preparing their country鈥檚 athletes for the 2022 Beijing Winter Olympics, reported that college soccer players who inhaled the gas five times a week increased their hemoglobin levels. A , in which subjects inhaled the gas five times a day, reached similar conclusions. Most recently, a by researchers in Norway combined altitude training with twice-daily carbon monoxide inhalation for a synergistic effect.

But there hasn鈥檛 been a single verified report of an athlete actually using this technique. I reached out off-the-record to contacts in several elite endurance sports, as well as researchers in the field, and none of them had heard even rumors of real-life usage. The risk, so far, is theoretical. The headlines during the Tour de France referred to the use of small doses of carbon monoxide to measure hemoglobin levels. This technique has long been used in elite sport to check how athletes are responding to altitude training, but the doses are too low to boost performance. There is a gray area here: Once you鈥檝e got the carbon monoxide device in the team van, there鈥檚 a temptation to use it. But would elite athletes, these paragons of super-fitness, really take such a dumb risk?

Whether rational or not, we all accept nonzero risks in pursuit of goals.

It鈥檚 a fair question. In the 1980s and 鈥�90s, Chicago doctor Robert Goldman circulated a now-infamous series of questionnaires among elite athletes, asking if they would take an undetectable drug that would make them unbeatable for five years鈥攁nd then die of the side effects. Roughly half the athletes accepted the bargain, he reported. Goldman鈥檚 Dilemma, as it鈥檚 now known, is often cited as evidence of the modern athlete鈥檚 off-the-charts focus on winning, regardless of the costs. And indeed, virtually all performance-enhancing drugs are associated with health risks, and that hasn鈥檛 harmed their popularity. 鈥淵ou have guys who will go to the funeral of a friend who died from this stuff, come home, and inject it again,鈥� an anonymous Olympic runner told Sports Illustrated in a 1997 article about Goldman鈥檚 Dilemma.

But it鈥檚 not clear whether Goldman鈥檚 respondents were taking the question seriously, or whether attitudes have changed. Recent attempts to replicate Goldman鈥檚 results raise doubts. A 2018 study from Duke University estimated the 鈥渕aximum acceptable mortality risk鈥� that nearly 3,000 athletes would accept in exchange for the guarantee of Olympic gold. No one took the deal if it meant certain death. Depending on the sport and the level of competition, athletes were, on average, willing to accept somewhere between 7 and 14 percent risk of a fatal heart attack.

That鈥檚 still a big risk. But it鈥檚 comparable, the researchers point out, to the risks people say they鈥檙e willing to accept in exchange for other life-changing outcomes, like relief from their rheumatoid arthritis. And it鈥檚 not fundamentally different from the types of risk you might encounter on mountain expeditions, in extreme sports, or in the backcountry. Whether rational or not, we all accept some risks in pursuit of our goals. So it seems unlikely that the theoretical possibility of a fatal mishap will be enough, on its own, to dissuade athletes from trying to get a boost from carbon monoxide.

In February, the UCI, cycling鈥檚 international governing body, to boost performance, while the use of single doses to measure hemoglobin will still be allowed. This may seem like one of those wishy-washy compromises that鈥檚 almost impossible to enforce: the substance itself is permitted, but you have to promise you鈥檙e using it for the right reasons. But I think it鈥檚 the right call. Anti-doping agencies should, of course, be trying to catch unrepentant cheaters. But they also have a crucial role to play in setting broader norms about what risks we should or shouldn鈥檛 be willing to accept in pursuit of gold. Motivated athletes will do whatever the rules permit鈥攕o let鈥檚 not ask them to suck on a tailpipe five times a day, any more than we would lock them in a nuclear sub with a crew of chain-smokers.

This piece first appeared in the summer听2025 print issue of 国产吃瓜黑料 Magazine. Subscribe now for early access to our most captivating storytelling, stunning photography, and deeply reported features on the biggest issues facing the outdoor world.

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For hikers, every day is leg day鈥攚hich makes mastering the best stretches for hiking an essential step.

Hiking uses your gluteal muscles, quadriceps, hamstrings and calves, and requires sturdiness of all the joints鈥攁nkles, feet, hips, and knees. Carrying a pack can create tension in your neck and using hiking poles can cause your arms to become sore.

Fortunately, targeted stretching before and after each hike can prevent injury and aid in recovery. A 2021 survey of studies published in showed that yoga and stretching were associated with less injury for hikers.

While trekking in Patagonia, I sometimes wondered if my legs would ever not feel sore again. After each day of 15-mile hikes, I returned to to practiced yoga in the designated yoga dome.听This daily practice gave my body the opportunity to recover with more ease and grace, rehydrating my muscles and freeing the lactic acid build-up. The following day鈥檚 hikes were met with less resistance in my joints and more intention in each step.

Try this series of stretches for hikes after (or before, or preferably both!) your next on-foot adventure. You鈥檒l be impressed at how much faster you will recover from those long miles of uphill climbs.

Child鈥檚 Pose with Bent Forearms

After miles on the trails, your entire body can feel tense and achy. Starting your post-hike practice in invites relaxation into your nervous system and musculature. You can also open up your chest by propping your elbows and forehead on blocks, bending your elbows, and placing your fingertips on your shoulders. This also adds a stretch for the triceps, which can become sore from using hiking poles.

Downward-Facing Dog Pose

After a day of hiking, especially if you have been carrying a big pack, some spinal decompression can be greatly appreciated, and this can be accomplished by any kind of inversion, including . It鈥檚 a fairly accessible inversion that provides gravity-driven lengthening for your . It also stretches your wrists and calves. If your calves feel particularly sore from going up and down the mountain, roll a blanket and place it under your heels for some extra support.

Thunderbolt Pose with Neck Stretches

When hiking, we often stare downward at the trail, which increases strain on the muscles that hold our head upright. Moving your cervical spine gently in every direction, as well as offering some traction can help ease any ongoing neck pain. Kneel on the mat and sit back on your heels, with your shins on the ground and knees hip width apart. (Place a block under your hips if you feel discomfort in your hips, knees or ankles). Sit tall and offer yourself some neck stretches.

Cat/Cow Pose

/Cow is one of my favorite poses to help you get back in touch with the integrity of your spine and to thoughtfully reconnect with your breath. The protraction and retraction of the shoulder blades can also ease soreness from wearing a backpack.The rhythmic motion of this pose helps to gently loosen along the entire spine and open space in the back of your shoulders.

Low Lunge

The work hard while you鈥檙e hiking, helping you lift your leg with each step forward. can decrease your stride length and cause your gluteus muscles to overwork, so you want to keep them as flexible and fluid as possible. Low Lunge is a great pose to relieve tightness and bring balance in the front and back of your hips. To add some chest opening, raise a climbing pole above your head and reach your arms back slightly behind your ears.

Low Lunge with Quadricep Stretch

Anyone who has hiked a mountain knows how much of a toll that takes on the quadriceps. This version of Low Lunge is a staple stretch for all hikers, and yet one we often neglect. Bring your foot closer to your buttocks for a deeper stretch, or away from your buttocks for more focus on the hip flexor. Place a blanket under your knee for additional support. Reaching back to grasp your foot also provides an additional stretch for the chest and front shoulder.

Half Splits

Your hamstrings work in conjunction with the quadriceps to bend your knees while you walk, and they鈥檙e especially important when you are climbing. Hamstring health is integral to hiking because they have to lengthen considerably when the knee extends and the hip flexes as the foot contacts the ground. If you have tight hamstrings, your knee won鈥檛 extend properly which will impact your gait, often causing knee, hip or back pain. Practicing is a great way to access hamstring opening, while also controlling how deeply you stretch. Place blocks under your hands if you prefer more back and gluteal lengthening. For an additional stretch for your shin muscles, press the sole of your front foot toward the ground.

Warrior I Pose with Hands in Reverse Prayer

is often thought of as a strengthening pose for the hips and legs, and it is. However, the positioning of the back leg also provides a stretch for the hip flexor, hamstring, and calf muscles. For a little less work in your front leg back out of the knee bend a bit. (It鈥檚 true, your front thigh 诲辞别蝉苍鈥檛 have to be parallel to the ground all the time, especially if your legs are tired from hiking!) A nice add-on to this pose is to bring your hands into reverse prayer or fist-to-fist. This gives a stretch to your shoulders and chest.

Pigeon Pose

Let鈥檚 talk buttock muscles: Our glutes do a lot of work for us day in and day out鈥揳nd they are literally built to help get hikers uphill. When we factor in the force of gravity and a heavy backpack, this greatly increases the work on the gluteus muscles and quadriceps in comparison to walking on a flat surface. To counter that workload, is a great posture to stretch your buttocks muscles. To provide an additional stretch of your quadriceps in your back leg, bend your knee and draw your heel toward your .

Half Lord of the Fishes

Hikers commonly have tight IT bands, and this rigidity can often manifest as lateral knee pain鈥損ain on the outside of the knee. If the gluteus muscles are too tight, (see Pigeon above), this can cause the IT bands to become even tighter. pose is a nice way to relieve tightness in the IT band, while also providing a chest opening spinal twist.

Thunderbolt Pose with Cow-Face Arms

If you hike fast, your ankles may be in a perpetually dorsi-flexed position. This can cause tightness in your tibialis anterior (your shin muscles), which can also cause ankle instability. Stretching the fronts of the lower legs will not only help you stay on the trails with a healthier stride, but it also feels so good. If this pose feels too intense in your knees or ankles (see neck stretches above), sit on a block for support. Also, a nice add-on, which stretches your triceps and forearms, is to bring your arms into , using your hiking poles instead of a strap to help your hands reach each other.

Breathing Exercises

When we hike, we are often so busy taking in the scenery or watching our step that we often forget to breathe in the beautiful forest or mountain air. Take a moment to practice some breathwork to remind yourself to stay fully open, present, and awake to all you鈥檝e accomplished, and all that is to come.

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Whether you鈥檙e running, biking, or climbing, your workout should always begin with a basic bodyweight warm-up to prime your muscles and joints for peak performance. The same goes for preparing for leg day at the gym.

Dynamic stretching, in which you move your muscles and joints through their full range of motion, helps your body prepare for the work ahead. As 国产吃瓜黑料 previously reported, this kind of movement helps improve blood flow, increase heart rate, and improve coordination and control.

The more specific the stretches are to the main activity ahead, the better. 鈥淭he simplest thing is to just get deeper into the motions you鈥檙e going to be doing,鈥� says , a physical therapist and spokesperson for the American Physical Therapy Association, based in San Francisco. So, for a squat session in the gym, you can begin with some deep bodyweight squats. Before a trail run, you might do some side steps to prepare for leaping over rocks and roots. Ahead of a bike ride, do a hip flexor stretch to bring movement to the muscles that will be working overtime in a seated position.

鈥淯nderstanding what muscles are at work [in the activity ahead] can help you build the best dynamic warm-up routine,鈥� says Malek.

There鈥檚 also value in tailoring your warm-up to your body鈥檚 unique needs. If you have a history of hip discomfort or tightness, add some extra stretches designed to improve range of motion in the hip joints, says Malek. 鈥淭here’s a lot of room to make it fit for you,鈥� she says.

6 Dynamic Stretches to Prepare for a Lower Body Workout

Before any lower-body-focused workout, Malek suggests doing dynamic stretches that target the hips, glutes, hamstrings, and calves, as well as the joints of the hips, knees, and ankles.

This routine should take about 15 minutes to complete if you do two sets of 10 reps for each movement.

1. Bodyweight Squats

Muscles and joints worked: glutes, quads, hamstrings, hip flexors, hip joint

• Begin by standing with your feet slightly wider than hip-width apart and your toes turned slightly outward. Your arms should hang by your sides; pull your shoulders back and down.
• Send your hips back and bend your knees at the same time, lowering your hips towards the floor as if you were sitting in a chair. As you begin this motion, raise your arms in front of you, no higher than shoulder height, keeping your gaze forward and your chest upright.
• Pause for a few seconds at the bottom of the squat before pressing through your feet and rising back up.

2. Squat Reach

Muscles and joints worked: glutes, quads, hamstrings, adductors; knee, ankle, hip, and shoulder joints

听

• Get as low as you can into a deep squat, so your buttocks are just slightly off the ground.听 Keep the back of your thighs as close to the back of your calves as you can manage without too much discomfort. Your feet should be slightly wider than hip-width apart, planted firmly on the ground with your toes pointed slightly outward.
• Press your arms against the inside of your knees.
• Twist your torso to your left and reach your left arm up into the air at the same time, allowing your right arm to press deeper into the inside of your right knee. Your gaze should follow your left hand upwards.
• Pause for a moment, then switch arms.
• After you鈥檝e completed one reach on each side, grab your toes with both hands and raise your hips until your legs are straight鈥攐r close to straight. That completes one rep.
• Keeping your fingers hooked under your toes, lower back into your deep squat to begin the next rep.

3. Half-Kneeling Hip Flexor Stretch

Muscles and joints worked: glutes, hip flexors, hip joint

• Begin in a half-kneeling position (essentially a ). One leg should be bent at the knee in front of you (a 90-degree angle) with your foot flat on the ground. Your other leg should be bent behind you (also at a 90-degree angle), with your shin and the top of your foot flat on the ground.
• Slowly lean your hips forward so that your knee bends even more (to about a 45-degree angle), feeling a stretch in the hip flexor of your rear leg.
• Hold that bent position for two or three seconds, then return to your starting point.
• Complete all repetitions on one side before switching sides.

4. Half-Kneeling Adductor Rock-Back

Muscles and joints worked: adductors, hip flexors, hip joint

• Begin on all fours.
• Straighten one leg out to the side and slightly behind you. You should feel a slight stretch in the groin of the outstretched leg, even without movement.
• Rock your hips back and hold for about five seconds to deepen the stretch. Then rock forward, bringing your shoulders over your hands. That鈥檚 one rep.
• Complete all repetitions on one side before switching sides.

5. Side Steps

Muscles and joints worked: adductors, quads, hamstrings, glutes, hip joint

• Begin standing with your feet together, hands by your sides.
• Jump your outside leg out to the side, then quickly bring your second leg to join it.
• Repeat on the opposite side.
• Continue alternating sides until all reps are completed.

6. Dynamic Calf Stretch

Muscles and joints worked: calves, ankles

• Place your hands against a wall with your arms outstretched at shoulder height.
• Step back about two feet away from the wall and lean forward until you start to feel a stretch in the back of your calves. Your upper body will be angled toward the wall.
• Pedal your feet, coming up on your toes, you鈥檒l feel a stretch in your calf as you press the heel back down to the floor.
• Continue alternating feet for the full set of repetitions.

Want more of听国产吃瓜黑料鈥檚 Health stories?听.

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Failure is a big topic in the weight lifting world these days. When you鈥檙e doing an exercise, do you need to push each set to the point that you literally can鈥檛 complete one more rep? Old-school practical wisdom says yes. More recent scientific studies have suggested that training to failure isn鈥檛 necessary, and might actually be counterproductive because it takes such a big toll on both your muscles and your mind.

The truth is probably somewhere in the middle, according to a in Medicine & Science in Sports & Exercise鈥攂ut the results lean toward the idea that failure isn鈥檛 necessary for most of us. The study finds that getting close to failure produces strength gains that are similar to going all the way. That said, training to failure does build a little more muscle mass at some locations. The results of the study also offer some useful clues for those of us seeking the biggest muscle gains from the least amount of time and effort in the gym鈥攏ot because we鈥檙e lazy, I hasten to add, but because we want to spend that time and effort in other ways.

Brad Schoenfeld and his colleagues at City University of New York (CUNY) Lehman College put 42 participants鈥�34 men and 8 women鈥攖hrough an eight-week full-body training program. One group was assigned to complete all their sets to failure while the other was instructed to always stop short of failure. The volunteers were all experienced lifters who had been hitting the gym at least three times a week for more than a year, which means there were no easy gains to be had. And the experimental lifting protocol called for just two workouts a week, with each workout consisting of just one set of nine different exercises. In total, each workout took about half an hour.

This idea of short, single-set workouts isn鈥檛 radical or new. Back in the 1970s, Arthur Jones, the inventor of Nautilus exercise machines, an approach that relied exclusively on single sets to failure. The problem is that pushing to true failure is no joke. It takes a lot of mental focus, and it also takes more time to recover. If your primary interest is another sport like running, you don鈥檛 necessarily want your legs to feel like lead the day after a strength workout. So it would be nice if it were possible to get most of the benefits of a hard workout while stopping short of true failure.

To test that theory, the approach Schoenfeld and his colleagues used is called 鈥渞epetitions in reserve.鈥� The subjects in the non-failure group were instructed to continue each set until they felt they had two repetitions in reserve, meaning that they would be able to squeeze out two more complete reps before failing on the subsequent one. It seems like a much more humane way to train鈥攁nd it also turned out to be fairly effective.

The most surprising result of the study is that both groups got measurably bigger and stronger even though they were working out less often than they were before the study period. That fits with a bunch of previous research on the 鈥�minimum effective dose鈥� for strength training. It 诲辞别蝉苍鈥檛 mean that half an hour, twice a week is sufficient to maximize your gains. But it does mean that those of us for whom strength training is mostly a means to some other end (like staying healthy, avoiding injury, or being able to carry a heavy pack) can make progress with a relatively modest investment of time.

As far as the efficacy of training to failure goes, there were a whole bunch of different outcomes in the study. The simplest were one-rep max in the bench press and squat, as measures of upper and lower body strength. To test explosive power, the researchers used a countermovement jump (CMJ), which simply involves squatting down then leaping as high as possible in a single motion. To test muscular endurance, they had the subjects complete as many reps as possible (AMRAP) on a leg-extension machine lifting 60 percent of their body weight.

The four tests of strength (bench press, squat, CMJ, and AMRAP) are at the bottom. The solid vertical line at 0.0 corresponds to no change after eight weeks of training. Both bench press and squat increased, with no significant difference between groups. For example, max squat increased by 13.2 percent on average in the failure group and 12.4 percent in the reps-in-reserve group. Same with muscular endurance (AMRAP). Power (CMJ), on the other hand, increased more in the group that trained to failure.

The picture was different for muscle size, which is shown in the upper part of the graph above. Researchers used ultrasound to measure various points along the mid and lateral quadriceps (MQ and LQ on the graph) as well as the biceps and triceps. In most (but not all) cases, training to failure produced bigger gains in mass鈥攚hich might be ideal if you鈥檙e working out for aesthetic reasons, but not necessarily if you鈥檙e training for a weight-to-strength ratio sport like cycling or climbing.

There鈥檚 a key caveat here, which is that estimating reps in reserve is an inexact art. To check how inexact it was, the researchers sometimes asked their subjects to keep going after they鈥檇 estimated they had two reps left. The estimates were fairly good and got better over the course of the eight-week study. But these were experienced lifters who had presumably experienced true failure many times before. For newbies, , it鈥檚 probably a good idea to do at least some training to failure so that you know what it feels like. Then, once you have a good internal benchmark, switch to a reps-in-reserve approach.

In some ways, this line of research reminds me of the current debate in the endurance world about Norwegian double-threshold training. The underlying premise of the Norwegian method is that hero workouts that leave you crumpled by the side of the track are counterproductive. Better to push hard enough to stimulate adaptation but not so hard that you can鈥檛 recover for the next workout. Those who hope to win bodybuilding competitions will undoubtedly鈥攁nd wisely鈥攌eep lifting to failure. On the other hand, for those who want muscle and strength but care more deeply about tomorrow鈥檚 run, keeping a rep or two in reserve sounds like a great plan.

For more Sweat Science, join me on and , sign up for the , and check out my new book .

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If your typical gym session warm-up begins and ends with a casual five-minute jog on the treadmill, you may be short-changing the impact of your workout. To enhance your performance and prepare your body for the movements ahead, add dynamic upper body stretching to your warm-up routine.

Dynamic Stretching Primes Your Muscles Before a Workout

During dynamic stretching, you take a muscle and joint through its full range of motion, mimicking the exercises you鈥檙e about to do, explained , a physical therapist and spokesperson for the American Physical Therapy Association, based in San Francisco. So if your strength session is going to include barbell or dumbbell rows, for example, you might warm up with a set of rows using a light elastic band, moving the same muscles and joints but at a lower level of intensity. To prepare for a day of kayaking, you might include some wrist rotations and shoulder rolls. Scapular protractions and retractions鈥攚hen you bring your shoulder blades forward and away from the spine and pull your shoulder blades backward and toward the spine, respectively鈥攜ou can get your shoulders ready for reaching, grabbing, and pulling on climbing holds.

鈥淵ou’re priming all those muscles and joints that are about to play a role in your workout,鈥� Malek says.

Unlike static stretching (when you get into a stretch and hold it for 30 to 60 seconds), dynamic stretching gets your muscles and joints warmed up by revving your heart rate and increasing blood flow to the area, says Malek. There鈥檚 a neuromuscular element too, she says, in which you鈥檙e also improving your coordination, proprioception (your body鈥檚 ability to sense its place and movement in space), and control.

The key is to keep moving throughout the stretch rather than holding in place. Fluid motions have been shown to improve performance in your main workout by . Doing dynamic stretching prior to a workout has been shown to during that activity and decrease the risk of exercise-related injury.

Before your next workout, try spending a few minutes priming your muscles for movement with dynamic stretches specific to your sport. 鈥淭hat would get you the most bang for your buck,鈥� says Malek.

Here are seven stretches that, done together, will work all the joints and most of the upper body muscles..

7 Dynamic Stretches to Prepare for Your Upper Body Workout

Before any upper-body-focused workout, Malek suggests doing dynamic stretches that target the arms and shoulders, the thoracic, cervical, and lumbar spine, and your core.

If you do two sets and ten reps for each movement, this routine should take you about 15 minutes to complete.

1. Arm Circles

Muscles and joints worked: shoulders (anterior and posterior deltoids), traps, rotator cuff, shoulder joint

• Stand with your feet shoulder-width apart
• Open your arms out to your sides and begin to rotate them in small circles forward, keeping your arms relatively straight (you can have a soft bend in your elbows)
• Continue to make your circles larger until you鈥檝e reached your end range of motion
• Reverse the circles, starting small and getting bigger as you go

2. Banded Upright Row

Muscles and joints worked: shoulders (anterior and posterior deltoids), traps, rhomboids, biceps, shoulder, and elbow joints

• Stand with your feet shoulder-width apart
• Loop a in a light weight under both feet and hold the opposite end in your hands (your hands should be slightly narrower than shoulder-width apart, and your knuckles should be facing forward)
• Keeping your torso upright, pull up on the band, drawing your elbows high up towards your ears. Pause when the band meets your chin.
• Slowly lower your arms down. Repeat.

3. Plank Scapular Protraction/Retraction

Muscles and joints worked: core muscles, pecs, lats, traps, rhomboids, serratus anterior, shoulder joints

• Begin in a straight-arm plank position with your hands directly under your shoulders (avoid raising your hips or allowing them to dip down, causing an arch in your back)
• While pressing your hands into the floor, squeeze your shoulder blades together, then push them away (the only part of your body that should be in motion is your shoulder blades)

FYI: If a full plank is too challenging, you can drop your knees to the floor .

4. Standing Open-Book Wall Rotations

Muscles and joints worked: shoulders (anterior and posterior deltoids), shoulder joint; cervical, lumbar, and thoracic spine

• Begin by standing sideways to a wall
• Take a small step back with the foot closest to the wall
• Raise both arms up in front of you and bring your palms together at chest height (the back of your hand closest to the wall should be in contact with the wall)
• Begin to reach your outside arm away from your opposite hand, opening up as wide as you can, rotating your torso as you open up
• Follow your moving hand with your head and your gaze

5. Thread the Needle

Muscles and joints worked: core muscles, thoracic spine, shoulder joint, and elbow joints

• Begin on all fours with your hands directly under your shoulders
• Lift your left hand from the floor and reach your left arm underneath your right, with the back of your left hand gliding along the floor
• Your left elbow will bend as you reach, and your right elbow will bend as well as you continue to reach across the floor. Allow your head to twist to the right.
• Try to keep your hips still throughout the movement, keeping the motion contained to your torso and arms
• Slowly slide your left arm back to the starting position
• You can repeat all repetitions on one side before stretching the other side, or you can switch sides with each repetition

6. Dynamic Chest Opener

Muscles and joints worked: pectorals, shoulders (anterior and posterior deltoids), shoulder joint

• Stand with your feet shoulder-width apart
• Bring your palms together with your arms straight at chest height
• Open your arms as wide as possible out to the sides, then bring them back together in the center

7. Wrist Rotations

Muscles and joints worked: wrists

• Sit or stand in a comfortable position
• You can extend your arms or keep your elbows bent at your sides
• Rotate your wrists outwards in slow circles
• Then rotate them inwards in slow circles

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Like all great villains, lactic acid has been misunderstood. We鈥檝e been blaming it for the pain we suffer during intense exercise for more than two centuries. There鈥檚 nothing worse, we say, than the 鈥渓actic burn鈥� that locks our failing muscles into immobility. More recent tellings of the story have tried to rehabilitate lactic acid鈥檚 reputation, insisting that it鈥檚 actually trying to fuel our muscles rather than shut them down. But that version 诲辞别蝉苍鈥檛 capture the full complexity, either.

Into this confusion steps , from veteran physiologists Simeon Cairns and Michael Lindinger. It鈥檚 a dense 35-page doorstop titled 鈥淟actic Acidosis: Implications for Human Exercise Performance,鈥� and the clearest conclusion we can draw from it is that the precise causes of muscle fatigue during intense exercise are still a topic of active research and vigorous debate among scientists. But the sudden popularity of baking soda as an acid-buffering performance aid has renewed conversations about how, exactly, lactic acid works in the body鈥攁nd how we might counteract it. Here are some highlights from the latest research.

The Lactic Backstory

The first scientist to draw the connection between exercise and lactic acid was J枚ns Jacob Berzelius, the Swedish chemist who devised the modern system of chemical notation (H2O and so on). Sometime around 1807, he noticed that the chopped-up muscles of dead deer contained lactic acid, a substance that had only recently been discovered in soured milk. Crucially, the muscles of stags that had been hunted to death contained higher levels of lactic acid, while deer from a slaughterhouse who had their limbs immobilized in a splint before their death had lower levels, suggesting that the acid was generated by physical exertion.

A century later, physiologists at the University of Cambridge used electric stimulation to make frogs鈥� legs twitch until they reached exhaustion, and high lactic acid levels. The levels were even higher if they performed the experiment in a chamber without oxygen, and lower if they provided extra oxygen. That finding helped establish the prevailing twentieth-century view: your muscles need oxygen to generate energy aerobically; if they can鈥檛 get enough oxygen, they switch to generating energy anaerobically, which produces lactic acid as a toxic byproduct that eventually shuts your muscles down.

There are two small problems鈥攁nd one big one鈥攚ith this picture. The first detail is that, while lactic acid can be measured in the muscles of dead deer and frogs, it 诲辞别蝉苍鈥檛 actually exist in living humans. In the chemical milieu of the body, what would be lactic acid is split into two components: lactate and hydrogen ions. That鈥檚 not just being persnickety about terminology: lactate and hydrogen ions behave differently than lactic acid would. In fact, they can have separate and sometimes even opposing effects.

The second detail is that lactate (and hydrogen ions) aren鈥檛 really produced because your muscles are 鈥渞unning out of oxygen.鈥� The chemical reactions that use oxygen to turn food into muscle fuel are efficient but slow, great for powering relatively easy and sustained exercise. But they can鈥檛 provide energy fast enough to supply an all-out sprint. For that, you鈥檒l eventually need to rely on lactate-producing anaerobic reactions, even if you鈥檙e huffing pure oxygen from a can.

The big problem with the old view of lactic acid is the idea that it’s a metabolic villain. It turns out that, far from being an inert byproduct, lactate can be recycled into fuel for your muscles. In fact, one of the key superpowers that well-trained athletes develop is the ability to reuse lactate more quickly. This rehabilitation of lactate鈥檚 reputation has been going on for now (though it still has ), but athletes are still left with an unanswered question: if lactate isn鈥檛 what causes muscle fatigue, what is?

What the New Review Reveals

The first thing that Cairns and Lindinger establish is that, yes, levels of lactate and hydrogen ions increase during intense exercise. This is most obvious during intense exercise lasting between about one and twenty minutes. Longer bouts of exercise are less intense, so they can be mostly fueled by non-lactate-producing aerobic energy, and bouts of exertion shorter than one minute simply don鈥檛 have time to produce much lactate.

The evidence is now clear that lactate itself 诲辞别蝉苍鈥檛 interfere in any significant way with muscle function. But lactate and hydrogen ions are produced simultaneously in exactly the same quantities during anaerobic exercise, which complicates the 鈥渓actic acid is a good guy after all鈥� narrative. Lactate may be great, but it comes with an equivalent helping of hydrogen ions鈥攁nd that may be a problem.

When you increase the concentration of hydrogen ions in a solution, you鈥檙e increasing its acidity. That鈥檚 how the pH scale is defined: it鈥檚 a measure of hydrogen ion concentration. During intense exercise, the pH in your fast-twitch muscle fibers (which seem to be particularly susceptible to hydrogen ion buildup) can drop from around 7.0 to 6.0. That change represents a ten-fold increase in the concentration of hydrogen ions鈥攁 situation that can wreak havoc on muscle contraction.

The idea that hydrogen ions are what cause muscle fatigue isn鈥檛 entirely straightforward either, though. When you start hard exercise, the concentration of hydrogen ions actually decreases for about 15 seconds while you use up another source of fast-acting muscle energy called phosphocreatine. And yet your muscles are already getting fatigued during this initial burst, losing some of their maximal force, while hydrogen ion levels are still lower than normal.

There鈥檚 also a disconnect when you stop exercising, or take a break between hard intervals. Hydrogen ion (and lactate) levels keep climbing for a few minutes, which is why the highest lactate levels are generally recorded several minutes after hard exercise. But you don鈥檛 get weaker after you stop exercising; you get stronger as you recover, despite the rising concentration of hydrogen ions. So hydrogen ions may play a role in muscle fatigue, but they can鈥檛 be the whole story.

Another possibility is that hydrogen ions may interact with other molecules to disrupt muscle contraction. The most prominent candidates are potassium and phosphate, both of which increase during exercise and are associated in some studies with muscle fatigue. What these and other candidates have in common is that there are a ton of conflicting results: they have different effects on muscle fibers depending on the level of acidity, the muscle temperature, and the test protocol. This suggests鈥攏ot surprisingly鈥攖hat there isn鈥檛 a single molecule that causes your muscles to lose their power. Instead, it鈥檚 the whole cocktail of things going on inside your muscles during hard exercise that matters.

What About the Burn?

Most of the research that Cairns and Lindinger describe deals with muscle properties: how quickly are your fibers losing their twitch force, and why? It鈥檚 true that, as a middle-distance runner, I鈥檝e sometimes staggered down the finishing straight of a race with the sense that my legs were literally ceasing to function. It鈥檚 an awful feeling to experience, but satisfying to look back on: you know you left nothing out there.

Far more common, though, is a softer limit. You feel a red-hot burn and spreading numbness in your legs, and you choose to back off a bit. This feeling that we used to describe as 鈥済oing lactic鈥� is significant in its own right. In interviews with athletes who鈥檝e begun using baking soda, a common theme is that they鈥檙e able to push harder for longer before feeling that burn in their legs, which in turn enables them to race faster.

One theory about the feeling of going lactic is that you鈥檙e literally starving your brain of oxygen. If you push hard enough, it鈥檚 not just your muscles that go more acidic; your whole bloodstream follows. Thanks to a phenomenon called the Bohr effect, rising acidity reduces the ability of your red blood cells to ferry oxygen from your lungs to the rest of your body, including your brain. In one study, all-out rowing caused oxygen saturation to drop from 97.5 to 89.0 percent, which is a big drop鈥攂ig enough, perhaps, to slow you down and contribute to the out-of-body feeling at the end of hard races.

We also have nerve sensors that keep the brain informed about the metabolic status of the muscles. These group III/IV afferents, as they鈥檙e known, keep tabs on the real-time levels of molecules like lactate and hydrogen ions. If you block these nerves with spinal injections of fentanyl, exercise feels great鈥攖oo great, in fact, because you鈥檒l lose all sense of pacing, go out too hard, then hit the wall.

The most telling finding about the lactic burn, in my view, was where they injected various molecules into the thumbs of volunteers in an attempt to reproduce that familiar feeling. Injecting lactate didn鈥檛 do it. Neither did injecting hydrogen ions, or ATP, a fuel molecule whose levels are also elevated during hard exercise. Injecting them in pairs didn鈥檛 do it either. But injecting all three at the levels you鈥檇 experience during moderate exercise produced a sensation of fatigue in their thumbs, even though they weren鈥檛 moving them. And injecting higher levels turned fatigue into pain.

That鈥檚 a distinction I try to keep in mind in the late stages of hard workouts, and at the crux of races. That burning feeling is real, and it鈥檚 associated with lactate and acidity and muscular fuel levels. But it鈥檚 just a feeling. The lactate and ATP are actually helping me. The hydrogen ions, in combination with various other metabolites accumulating in my muscles, not so much. They鈥檒l eventually stop me. But until they do, I can keep pushing.

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