All training affects your hormone, or endocrine, system.
It鈥檚 important, says Anthony Hackney, a professor of exercise physiology at University of North Carolina-Chapel Hill and the co-author of Sports Endocrinology, to understand the balance of hormones. The key hormones for an athlete to know about are growth hormone (or human growth hormone, HGH), insulin and insulin-like growth factors, cortisol, and testosterone.
Growth hormone triggers the adaptive response in your muscles, says Tom Cotner, Ph.D., the running coach for Seattle-based Club Northwest. Growth hormone is an anabolic hormone that promotes growth. It targets the muscles and cells that are being stressed by exercise and makes them receptive to adaptation. The muscles actually adapt during recovery.
We naturally secrete growth hormone during the delta wave part of sleep, but as we get older we have less and less time in that deep sleep. During exercise, we also secrete growth hormones but in smaller quantities. It doesn鈥檛 kick in, either, until after about 10 minutes of exercise, Cotner says, and there are diminishing returns after 75 minutes.
Because growth hormone is secreted from the pituitary gland in response to energy expenditure it鈥檚 possible to 鈥済ame the system,鈥 Cotner says, by training more than once a day, doing more intense exercise, or taking an ice bath after exercise, which expends energy.
But, as the weeks of exercise accumulate, the amount of growth hormone secreted for anyone workout decreases and your body adapts. If you really wanted to 鈥渟ee the hormones go crazy,鈥 Hackney says, you鈥檇 get the most response from being very out of shape and then starting to work out.
The most commonly overlooked hormones involved in exercise are the insulin-like growth factors and insulin. Insulin-like growth factors are stimulated by growth hormones and bind to cells to regulate cell growth and processes. Insulin oversees the cells鈥 uptake of glucose and storage of glycogen, necessary to ensure we have the right energy pathways available for our training.
In the regular course of things鈥攊f you鈥檙e eating well, sleeping, and exercising鈥攖hese hormones work to self-regulate and maintain a balance.
鈥淪ome are going up, some are going down,鈥 Hackney says.
We can throw that balance out of whack, though, from overtraining. 鈥淵ou can overload your endocrine system,鈥 Cotner says.
Cortisol is released from the adrenal gland and is an anti-inflammatory and a catabolic hormone that breaks down cells. In an average person, cortisol breaks down about 1 percent of muscle proteins daily, which are then replaced as induced by growth hormone and insulin-like growth factor. With training, cortisol breaks down 3-5 percent of muscle proteins in the body every day, Cotner says. Too much training releases too much cortisol and essentially breaks down too many proteins.
Too much training can also decrease the levels of testosterone in the body. Testosterone, found in both men and women, increases muscle mass and decreases recovery time. But while intense workouts can increase testosterone levels, too much long, easy training can drive them down.
Overtraining is the most likely thing to throw off an athlete鈥檚 hormone balance, which leads to all the symptoms associated with over-training: sleeplessness, extreme muscle soreness, elevated resting heart rate, or overall fatigue. Generally, if you experience those symptoms, you should dial it back. But knowing exactly how much training is too much can be challenging.
鈥淚f I knew exactly how much was too much, I鈥檇 be a lot richer,鈥 Hackney says.
Other things that can impact the hormone balance include life stress, which causes a release of cortisol, epinephrine and norephedrine. A lack of sleep can stall your secretion of growth hormone, as can alcohol, Cotner says. One beer, he says, can decrease the amount of growth hormone secreted by 25 percent. Age also decreases the amount of growth hormone and slows down the entire system. That鈥檚 why older athletes often experience the two-day lag effect of soreness from a workout鈥攚hich can also happen to young female athletes, who have less growth hormone and testosterone.
Not eating enough calories, a particular problem for female athletes, can cause a disruption in the whole system. The right mix of protein (6 grams) to carbohydrates (30 grams) in the recovery window after a workout helps delay cortisol secretion and getting enough iron is essential to red blood cell production, regulated by naturally-occurring EPO. Any sickness or trauma will also force your body to prioritize hormone regulation to those things first.
Trying to bump up levels of some hormones is common in a variety of forms. People sleep in altitude tents to increase levels of EPO naturally by decreasing oxygen supply. Over-the-counter supplements promise to increase testosterone or HGH levels. But 鈥渁 lot of those things don鈥檛 work,鈥 Hackney says.
Even the things that do work in the short-term鈥攔esistance exercises have been shown to elevate short-term levels of growth hormone, testosterone and insulin-like growth factors鈥攁ren鈥檛 proven to make you faster in the long run, Hackney says.
Illegal doping agents definitely increase hormone levels and can sometimes increase performance, both Hackney and Cotner say. But, there are legal consequences, severe health consequences, and sometimes even death from messing with your hormone balance artificially. The complicated system is good at self-regulating and it鈥檚 hard to know what all the side effects of changing one thing will be.