In the last years endurance sports, defined in the PASSCLAIM document of the European Commission as those lasting 30 min or more, are increasing in popularity and competitions as half marathons, marathons, even ultramarathons, half Ironmans, or Ironman competitions attract more and more people.
They are competitions which can last hours, or days in the more extreme case of ultramarathons.
Athletes at all levels should take care of training and nutrition to optimize performance and to avoid potential health threats.
In endurance sports the most likely contributors to fatigue are dehydration and carbohydrate depletion (especially liver and muscle glycogen).
Dehydration and endurance sports
Dehydration is due to sweat losses needed to dissipate the heat that is generated during exercise. To prevent the onset of fatigue from this cause, the nutritional target is to reduce sweat losses to less than 2–3% of body weight; it is equally important to avoid drinking in excess of sweating rate, especially low sodium drinks, to prevent hyponatraemia (low serum sodium levels).
Muscle glycogen and blood glucose are the most important substrates from which muscle obtains the energy needed for contraction.
Fatigue during prolonged exercise is often associated with reduced blood glucose levels and muscle glycogen depletion; therefore, it is essential starting exercise/competition with high pre-exercise muscle and liver glycogen concentrations, the last one for the maintaining of normal blood glucose levels.
Other problems which reduce performance and can be an health threat of the athlete, especially in long-distance races, are gastrointestinal problems, hyperthermia and hyponatraemia.
Hyponatraemia has occasionally been reported, especially among slower competitors with very high intakes of low sodium drinks.
Gastrointestinal problems occur frequently, especially in long-distance races; both genetic predisposition and the intake of highly concentrated carbohydrate solutions, hyperosmotic drinks, as well as the intake of fibre, fats, and proteins seem to be important in their occurrence.
Burke L.M., Hawley J.A., Wong S.H.S., & Jeukendrup A. Carbohydrates for training and competition. J Sport Sci 2011;29:Sup1,S17-S27. doi:10.1080/02640414.2011.585473
Saris W.H., Antoine J.M., Brouns F., Fogelholm M., Gleeson M., Hespel P., Jeukendrup A.E., Maughan R.J., Pannemans D., Stich V. PASSCLAIM – Physical performance and fitness. Eur J Nutr. 2003;42(Suppl 1):i50-i95. doi:10.1007/s00394-003-1104-0
Jeukendrup A.E. Carbohydrate feeding during exercise. Eur J Sport Sci 2008:2;77-86. doi:10.1080/17461390801918971
Jeukendrup A.E. Nutrition for endurance sports: marathon, triathlon, and road cycling. J Sport Sci 2011:29;sup1, S91-S99. doi:10.1080/02640414.2011.610348
Sawka M.N., Burke L.M., Eichner E.R., Maughan, R.J., Montain S.J., Stachenfeld N.S. American College of Sports Medicine position stand: exercise and fluid replacement. Med Sci Sport Exercise 2007;39:377-390. doi:10.1249/mss.0b013e31802ca597
Shirreffs S., Sawka M.N. Fluid and electrolyte needs for training, competition and recovery. J Sport Sci 2011;29:sup1, S39-S46. doi:10.1080/02640414.2011.614269