The half marathon is the most popular of all road-running events, but many runners are confused about fueling鈥攏ot just during the race but also the preparatory training sessions before the event. Should you be consuming in-race and in-training carbohydrate drinks and gels, or are they best reserved for the marathon distance?

Long-Term Burn

To answer this question, we need to understand two simple concepts about the energy demands of running a half marathon. For all athletic events lasting more than a few minutes, a large proportion of the energy is supplied from oxygen-fueled aerobic metabolism in the muscle cells, where carbohydrates and fat are combined to release the energy required for muscle contraction. Once the duration exceeds 30 minutes or so, nearly all energy is supplied this way. Given that the world record for the half marathon currently stands at 58:01, you can see that this event is fueled almost exclusively by aerobic metabolism鈥攚hether you鈥檙e an ultra-elite, middle-ranking or weekend novice runner.

Event Duration and Energy Source During Maximal-Effort Exercise

Hybrid Fueling

The second concept concerns the ratio of fuels (carbohydrate and fat) that are oxidized in muscles during aerobic exercise. Research shows that once exercise intensity increases beyond 鈥渕oderate,鈥� the proportion of fat utilized for fuel declines, while carbohydrate utilization increases, until at hard or very hard intensities, nearly all of the energy to fuel exercise .

Fat vs. Carbohydrate Burning at Different Exercise Intensities

More accomplished runners will almost certainly be working near lactate threshold throughout the half-marathon distance, relying mainly on stored muscle carbohydrates for their energy source. Novice and recreational runners with lower levels of aerobic fitness will tend to work at slightly less intensity, which in theory means they will derive a slightly higher proportion of energy from fat.

Just to confuse things however, the research also shows that more highly-trained an endurance athlete, compared to their less fit contemporaries. In reality, this means that both highly and lesser-trained athletes will utilize a little fat for fuel during a half marathon.

However, the 鈥攁nd this is what counts for performance. The pivotal role of carbohydrates鈥攔ather than fat鈥� has been confirmed by research; during exercise at 85% of maximum aerobic capacity (not dissimilar to the intensity of a half marathon), , contributing 83鈥�91% to total energy expenditure鈥攚ith only a small contribution from fat-based fuel.

Whether you鈥檙e a 1:15 or 2:15 half marathoner, carbohydrate fueling is critical to performance. That carbohydrate will consist mainly of stored muscle carbohydrates (glycogen).

Limited Storage Tank

The final factor to consider is the size of the body鈥檚 carbohydrate storage. Here the elite runner has a clear advantage because muscle glycogen storage is only enough to fuel around two hours鈥� worth of high-intensity exercise. The elite runner will still have plenty left in the tank as he/she crosses the finish line鈥攗nlike slower runners who will be on the road nearer to two hours and maybe longer. For these less-elite runners, ever lower muscle glycogen levels will likely result in heavy limbs and a noticeable increase in effort and heart rate for the same pace鈥攊nevitably forcing a reduction in pace.

Optimizing Carbohydrate Nutrition

Getting carbohydrate nutrition right is essential for running a good half marathon. Let鈥檚 see what this means in terms of the actual pre-race diet, the race itself and for training.

Pre-Race Diet

All runners, whether elite or non-elite should arrive at the start line with muscle glycogen stores fully topped up. This means consuming a carbohydrate-rich diet (high in bread, pasta, rice, potatoes, corn, oats, beans, lentils, etc.) in the two to three days before the race. This also assumes of course that you will be resting up during this period in order to conserve energy and be fresh for your race! And since glycogen is 鈥渇ixed鈥� into the muscles with water, it鈥檚 imperative that you also consume plenty of fluids and minimize or eliminate alcohol intake (which is dehydrating).

Needless to say, all runners should consume an easily digested but carbohydrate-rich breakfast on the morning of the race, preferably containing gently releasing energy foods, such as oat-based cereals, in order to avoid energy swings and troughs.

Exercise Duration and Carbohydrate Intake Recommendations

In-Race Nutrition

Highly trained runners who are confident of completing the race in less than 75 minutes or so have no particular need to consume carbohydrate drinks or gels during the race to top up glycogen stores, although fluid might be desirable in hot conditions. Where race duration is expected to exceed 75 minutes, some modest use of carbohydrate drinks and gels (supplying around 30 grams per hour) is recommended to top up stores (see above). For race durations of 120+ minutes, carbohydrate supplementation supplying 60鈥�75 grams per hour will help stave off the worst effects of glycogen depletion. The golden rule of any carbohydrate supplementation, however, is to try it in training first. Gels in particular may not be well tolerated by some runners, and research shows that the gastric distress they cause .

Half Marathon Training Nutrition

During preparation, most runners鈥� training sessions will be of shorter duration than their anticipated race time鈥攖hus carbohydrate supplementation is usually not necessary. However, the use of carbohydrate drinks and gels is popular during training on the basis of helping to keep muscles 鈥渢opped up鈥� and so reduce the likelihood of fatigue in subsequent sessions. There鈥檚 some merit in this, particularly for slower runners performing longer sessions, or where it鈥檚 difficult to consume a carbohydrate-rich meal after training.

There鈥檚 good reason, however, not to habitually use carbohydrates during training: When carbohydrates are freely available, muscles will become less efficient at fat burning. While your fat-burning capacity is not (as we鈥檝e seen) a deal breaker for half-marathon performance, performing some regular training sessions that enhance fat burning is good for reducing body fat and increasing sustainable power-to-weight ratio. All things being equal, lower levels of body fat (and therefore weight) will reduce your energy expenditure and oxygen consumption at any given pace鈥攐r, to put it another way, your maximum sustainable pace will be higher. It鈥檚 no coincidence that all elite runners have low body fat levels and excellent power-to-weight ratios!

Other Factors that Affect Fueling and Performance

Although carbohydrate nutrition is critical for half-marathon performance, don鈥檛 forget about the importance of hydration, especially in warm conditions. Drink plenty of fluids prior to the race to ensure you鈥檙e fully hydrated at the start. Studies suggest that you so runners completing the race in less than 75 minutes should have no real need to drink unless they feel thirsty. However, slower runners taking more than 90 minutes should plan to consume fluids on the run, even in more temperate conditions.

For both elite and non-elite runners, , helping to stave off fatigue, thereby extending endurance, and for half-marathon performance.

Pre-race nitrate (in the form of beetroot juice) , which could particularly benefit slower runners, but . Don鈥檛 forget the golden rule though鈥攖ry any supplementation strategies out in training before using them in a race!

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Research has found that optimum intakes of vitamin D in adults provide significant from degenerative illnesses such as heart disease, multiple sclerosis and a number of different cancers. Runners in hard training, however, have other very good reasons why your vitamin D intake matters鈥攏ot just for health, but for performance too.

Why Do Runners Need Vitamin D?

Stay Healthy

A growing body of evidence suggests not only that sub-optimum vitamin D status harms immunity, but also that boosting vitamin D intake improves immunity. For example, when scientists 225 endurance athletes over the winter period, they found that a significantly higher proportion of those who were vitamin D 鈥榙eficient鈥� came down with an upper respiratory tract infection (URTI 鈥� coughs, colds, sore throats, etc.) and suffered worse symptoms than those in the 鈥榦ptimal鈥� status group. Another found that supplementing 5000IUs per day with vitamin D鈧� for four weeks during the winter boosted immune function and reduced the incidence and severity of URTIs in taekwondo athletes. Other recent have provided strong evidence that 1) poor vitamin D status is linked to a higher incidence of URTIs and that 2) increasing vitamin intake, especially over the winter period, reduces the incidence and severity of URTIs.

Avoid Stress Fractures and Muscle Injuries

Vitamin D is needed for the formation of strong, healthy bones, and clearly shows that sub-optimum intakes of vitamin D can greatly increase the risk of stress fracture in runners. There鈥檚 also good that a poor vitamin D status increases the risk of muscle and other soft tissue injuries in athletes鈥攑articularly in the lower limbs and core muscles.

Improve Power and Strength

Some suggests that in runners with an optimum vitamin D status, and that higher intakes of vitamin D can some power and strength measures in athletes. However, the on performance is somewhat patchier, and some studies have found no benefits.

Why We Go Short of Vitamin D

Numerous have shown that vitamin D insufficiency or outright deficiency is rife, even in the affluent West. The situation is no better when it comes to runners; on athletes from the UK, US, Australia, Scandinavia and the Middle East have all found high rates of vitamin D insufficiency or even out-and-out deficiency. Why are so many people鈥攊ncluding athletes鈥攕ub-optimum in vitamin D?

1. Our diets have relatively few vitamin D rich foods, which means it鈥檚 easy to go short.
2. Indoor lifestyles combined with advice to avoid the sun and cover up reduces the opportunity for vitamin D synthesis in the skin when exposed to strong sunlight.

Vitamin D Status and Sunshine

Vitamin D is an essential nutrient, belonging to a group of fat-soluble steroid-like compounds of which there are two major forms: Vitamin D₂ and vitamin D₃. Vitamin D₃ is the most active form in the body and is produced in the skin after exposure to UVB (ultraviolet) rays from the sun.

The role of sunshine in ensuring optimum vitamin D status cannot be overstated. In the summer months, sunlight exposure is an incredibly efficient way of supplying vitamin D. With just 录 of the body鈥檚 skin exposed (eg wearing a T-shirt and shorts), the average fair-skinned person can synthesise enough vitamin D for a day with just six minutes exposure to the midday sun!

The UVB content in sunlight is a function of season and latitude, however. During the winter months in the northern states, there is very little UVB in sunlight鈥攅ven on the brightest winter鈥檚 day. And the further north you live, the there are with useful UVB.

In southern Florida, vitamin D synthesis is possible all year round, while in Seattle, it鈥檚 possible only from March to October. In Alaska, you can only get vitamin D from sunlight between early May and late August. This explains why a lot of athletes enter the winter period with an adequate vitamin D status, but by the mid-late winter period, many have become sub-optimum or even outright .

Vitamin D and Diet

In the diet, vitamin D can be only be found naturally in a small range of foods. These include oily fish (such as salmon, trout and sardines), eggs, milk (which is fortified) and some meats. By contrast, vegetables, fruits, grains, cereals, nuts and seeds contain very little vitamin D. The US National Institute for Health (NIH) a dietary vitamin D intake of 600 international units (IUs) per day. However, dietary needs are strongly influenced by your exposure to sunlight.

Some Good Sources of Vitamin D

Source: USDA and “Canadian Nutrient File 2010”

How Can I Ensure My Vitamin Intake is Sufficient?

• Try to consume plenty of vitamin D-rich foods (oily fish, eggs and vitamin D-fortified produce) at all聽times of the year.
• Use the 鈥榮unshine zone鈥� map above to determine when vitamin D supplementation should be considered.
• To confirm your vitamin D status, considered getting it checked鈥攅ither through your physician or using a home blood-testing kit.
• If your blood level is below 75nmol/L, consider supplementing with 1000-2000IU of vitamin D₃ (not D₂) per day until your status is improved鈥攔egardless of season.
• During the summer months, try to regularly expose your skin to some strong sunshine for 5鈥�15 minutes before covering up or applying sunscreen/sun block. Regular sun exposure can help build up your body鈥檚 vitamin D stores in readiness for the winter months ahead.
• Consider a winter break nearer to the equator to boost your flagging vitamin D levels.

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