You’ve trained hard for months, covered 100’s of kilometers pounding pavements and powering up hills, your equipment is the best around. Bring on the race! There is little doubt your time will be great and all the effort, hours and hard work will pay off, no stone has been left unturned.....or has it?
What will you eat in the days leading up to the race? What will you drink while racing? And how much? Or will you work it out depending on how you feel on the day?
Have you ever run out of energy and had to retire? Collapsed after the finish line? or simply endured the race and dragged yourself around the course? If so, the chances are you ran out of fuel and were heat exhausted.
Correct nutrition can minimize and delay performance limiting situations such as fatigue, impaired decision making and gastrointestinal upset, complements training effort and enables you to meet your own personal goal.
Consider factors about the race itself including duration, your anticipated split times , time of day the race starts, environmental conditions such as temperature and humidity, availability of food and fluids at aid stations and whether you want to use that or carry your own, whether there will be someone at the finish line with supplies, travel plans to and from the race.....
The Fuel Story
Muscles primarily use glucose to fuel the work of contraction. Glucose is the simplest unit of carbohydrate that all carbohydrates are digested into. Whether the food is sugar, honey, bread, milk, potatoes, pasta, fruit, rice or oats the body breaks it down into glucose before it’s available for use by the body. Some foods take longer to digest than others which means glucose may be quickly available for use or it may be substantial amount of time before the glucose is available. Depending on when the carbohydrate is needed there is benefit from both readily available and more complex, slowly digested carbohydrate. If glucose is not needed immediately by the body it is stored as glycogen, a small amount in the liver and a larger amount in muscles. Glycogen may be quickly broken down into glucose for use by the cells when needed. It is this glycogen store which will fuel exercise, although it is not large enough to be relied upon to support exercise beyond about 60-90 minutes. Well trained athletes physiologically adapt and have larger muscle glycogen stores enabling them to better fuel exercise. Fat may fuel endurance exercise following training adaptations where athletes produce more transport enzymes needed to mobilize fat transporting it into the cells for use. Lactate is likely to be produced during sprints, hill climbs and other episodes of intense work. Lactate is transported to the liver and converted into glycogen from which glucose can be released to fuel more exercise.
The Hydration Story
Exercise generates heat which must be removed from the body, primarily through sweat evaporation from the skin. As body heat increases heart rate increases, perceived work level is higher and the rate and degree of fatigue increases. Body fluid losses above 2% body weight increase the risk of delayed gastric emptying, bloating, nausea and vomiting, diarrhoea and reduced rate of fluid absorption from the gut. To put this level of dehydration in context, 1400ml fluid loss in a 70kg person equates to 2% reduction in body weight. Even mild dehydration affects brain function, vision and speed of decision making. If you're walking or jogging this is unlikely to have any consequence, but if cycling at speed, delayed decision making can be disastrous.
Avoiding dehydration is not as simple as drinking plenty of water. Water alone is sufficient up to 60 minutes of exercise but above that the body needs help retaining fluid. Sodium in salt helps water retention and reduces urine output, its effect being enhanced if carbohydrate is also consumed. Isotonic sports drinks are ideal.
Fluid requirements vary hugely between individuals and also vary with temperature, humidity, intensity of exercise and race duration. Any endurance race in hot and humid conditions will lead to large fluid losses. Although less likely in the tropics, there is a danger of over drinking causing lowered blood sodium and the potentially fatal condition of hyponatraemia. Hyponatraemia is more likely in athletes running slower, long duration races in cooler conditions and where the opportunities to drink are great. Fluid requirements racing in Malaysia will be significantly higher than for the New York Marathon. Sweat rates are lower when air moves over the skin causing sweat evaporation and hence skin cooling. Fluid losses will be less cycling than running. Humidity reduces evaporation rates and increases fluid requirements.
Estimate your own sweat losses on a number of training sessions by weighing yourself naked before and after training. Record the amount of fluid drunk. For example, starting weight 70kg, weight after training for 2 hours 69kg, 1000ml drunk. Total sweat loss 2000ml or 1000ml/hour. Repeat this exercise a number of times over training sessions of different length and intensity to get an estimate of your race day fluid requirements. It is unnecessary and unrealistic to exactly match fluid intake to expected losses but it is useful to know a ball park figure.
In addition to individual variation in sweat rates, loss of salt in sweat varies. People may sweat bucket loads of not very salty sweat or a small amount of very salty sweat. Signs of high sodium losses are sweat stinging your eyes, white staining on your tea shirt once sweat has dried and crusty deposits on your skin once sweat has dried. The Australian Institute of Sport can measure sodium concentrations of sweat. This may be arranged through a sports dietitian and must be done in conjunction with measuring fluid balance.
"Clinical Sports Nutrition, fourth edition", by Louise Burke and Vicki Deakin.
"The Complete Guide to Food for Sports Performance, third edition", by Louise Burke and Greg Cox.
Written for Metasport. The full article can be found here.