Triathlon, swimming

Endurance athletes' energy requirements are far higher than the average due to the large output as well as their raised metabolisms from the training. Unless the intensity of the event is low enough for fat to be used as the primary fuel, endurance athletes need to make up the bulk of their energy intake from carbohydrates. Athletes also need to ensure that they consume enough protein, fats & oils as well as vitamins, minerals & other micro-nutrients to support recovery from training. In order to maximise performance it is important that the athlete gets to the start line in peak physical condition & with maximum energy stores i.e. maximum levels of muscle glycogen. It has been known since the Swedish studies in the 1960s that supra-normal levels of glycogen in the muscles enhances performance in events that last longer than 60 minutes.

In terms of macro-nutrients it is recommended that endurance athletes in training consume between 6 - 8.5g of carbohydrate, 1 - 1.4g of protein & 1 - 1.4g of fat per kg of lean body mass per day (lean body mass is used for accuracy). For example an 80kg athlete with 10% body fat would require between 1,728 - 2,448Kcal from carbohydrates, 288 - 403Kcal from protein & 648 - 907Kcal from fat for a total of between 2,664 - 3,758Kcal per day (giving an average ratio of 70:10:20). This is a wide range which would need to be narrowed according to the athlete;s specific energy output & eating preferences. In order to calculate the total daily energy expenditure, energy output needs to be added to the athlete's basal metabolic rate (BMR). The Katch-McArdle formula has been chosen to estimate the BMR for accuracy as it uses lean body mass thus eliminating the assumptions about body composition. BMR = 370 + (21.6 X lean mass in kg) → 370 + (21.6 X 72) = 1,925Kcal/day. In the absence of direct calorimetric methods it would be necessary to estimate the output based on the athlete's training diary / training plan. For brevity in this example an activity multiplier will be used. As this is an endurance athlete preparing for a competition 1.725 (hard daily exercise/sports) & 1.9 (hard daily exercise/sports & physical job or 2x day training, i.e marathon, contest etc.) are used as the bounds giving a range of 3,321 - 3,658Kcal/day, confirming the calculation previously using the macro-nutrient requirements.

In order to maximise the nutrient intake it is recommended that a wide variety of natural whole foods are chosen. As the emphasis is on carbohydrates this means emphasising whole grains, fruits & vegetables. This will ensure adequate intake of vitamins, minerals & other micro-nutrients along with dietary fibre. As whole grains & potatoes are relatively high in protein & other sources of protein (legumes, meat etc.) will also be consumed there will be no need to supplement. The Physicians Committee for Responsible Medicine's Power Plate is a useful resource for the strict vegetarian or vegan to plan their diets. As long as the athlete eats a variety of foods they are comfortable with, bearing in mind their macro-nutrient requirements, this diet could be used throughout the season & even in the week building up to the competition. Along with rest & recovery, maximising muscle glycogen stores is a priority in the final week before a competition. Traditional methods of carbo-loading have been less than perfect, fortunately there are alternatives.

Carbo-loading is a process where, in the last week before an event, the athlete drives down muscle glycogen levels, aiming to have them at their lowest 3 - 4 days before the event, sometimes through a change in diet to a low carbohydrate, high fat diet & invariably with high intensity training lasting 60 minutes or more. The athlete will then switch to a very high carbohydrate diet for 3 – 4 days with at most light intensity training to drive up glycogen levels. While this strategy succeeds in achieving supra-normal levels of glycogen, 130-150 mmol/kg wet weight (‘normal’ levels are about 80-120) there are often unwanted side effects. The switch to the low carbohydrate, high fat diet often leaves athletes irritable & sometimes even harms their confidence. The high intensity training disrupts tapering, adds stresses (wear & tear) & risk of injury to a body that is healing to peak for an event. Often athletes overload themselves in the carb-loading phase & end up feeling bloated & sluggish on race day. A simple solution is for the athlete to continue with their usual high carbohydrate diet while tapering. The lack of energy output will enable the body to store more of the consumed energy. A possible pitfall with this strategy is that the levels of muscle glycogen may not reach the same levels. There is however another possibility.

Research carried out at the Department of Human Movement and Exercise Science at the University of Western Australia has shown that it is possible to raise muscle glycogen levels to supra-normal levels with a 3 minute high intensity workout (130% of VO2max) followed by 24 hours of very high carbohydrate intake (in the form of a maltodextrose-rich drink) which was started within 20 minutes of the workout. In the study trained endurance athletes with an average glycogen level of 109 mmol/Kg wet weight before the trial had those levels pushed to 198.2 mmol/kg, an 82% increase. It has also been shown that these high levels can be maintained, in the absence of training & with sufficient carbohydrate intake, for 2 - 3 days.

This strategy therefore eliminates the short comings of traditional carbo-loading. In essence the athlete would continue with their normal diet with no risk of lethargy or gastric discomfort, while tapering in the week before the event. The day before the event the athlete would warm up, then train at maximum intensity for 3 minutes, cool down & start consuming large quantities of carbohydrates within 20 minutes & be ready for the contest the next day. It is recommended to use carbohydrate sources with a high glycaemic-index (with glycaemic-index values above 60): muffins, oat bread, cornflakes, Raisin Bran, sweet corn, couscous, rice cakes, dried dates, dried figs, papaya, raisins, watermelon, fruit bars etc.. If there are concerns about consuming high-glycaemic index foods it's worth bearing in mind that many of the foods consumed heavily and regularly by elite Kenyan runners have very high glycaemic indices. Maize-meal porridge has a glycemic index of 109. (glucose the standard is set at 100); millet-flour porridge (107) and Kenyan rice, a true staple (112). Although there should be no major side effects associated with this plan it is important to test it several times during training before. If there are any concerns about the 3 minute high intensity workout the day before the event it could be shifted to 2 - 3 days before the event & the athlete could still have supra-normal levels of glycogen in their muscles.

A further application of the research would be to prevent glycogen dips during training. After prolonged exercise consisting of only moderate-intensity work i.e. long slow distance training, it usually takes about 24 hours for muscle glycogen stores to return to pre-exercise levels, even when a high carbohydrate diet is followed. The true glycogen-loading following such exercise usually only occurs during the second and third days afterwards. By adding a 3 minute high intensity burst at the end of these workouts the athlete can speed up glycogen store restoration. It may even be possible to build muscle glycogen concentrations rather than just maintain them.

Dehydration is always a concern during periods of heavy exercise & competition so the athlete also needs to consume enough water along with the appropriate electrolytes. Over-hydration however, also caries risks (more on hydration in a future post).

- mec