Now that the competitive period of many sports begins, including triathlon, it is important to remember the importance of reaching the day of competition with glycogen deposits as full as possible. Carbohydrates (CHO) are the main energy substrate when we exercise at moderate or high intensity. Therefore, glycogen depletion (the storage form of CHO) is one of the major factors limiting performance in endurance sports. A high availability of CHO during exercise will prevent the reduction of blood glucose or hypoglycemia (also known as the popular area as drained or wall), and also allow to maintain a greater intensity of exercise.
Various nutritional strategies have been studied to increase the synthesis of glycogen and thus get to the competition with deposits in the best conditions (Burke et al., 2017). A classic study that popularized the term “window of opportunity” or “metabolic window” found that the synthesis of glycogen was much greater if the CHO intake was made in the two hours immediately after an exercise session that if performed later (Ivy et al., 1988). This is because, although after intense training there is a depletion or “depletion” of glycogen levels, this situation also causes the activation of a series of mechanisms (increased sensitivity to insulin and cell membrane permeability to glucose, and stimulation of the enzyme glycogen synthase) that favor its re-synthesis (Prats et al., 2009). Therefore, if there is little time between a session of intense exercise (with the consequent depletion of glycogen) and the next session, as occurs for example when performing two sessions in the same day or when competing several times in a day, it is important to provide the CHO as soon as possible.
As low levels of glycogen stimulate its synthesis, traditionally pre-competitive strategies have supported that consisted in the depletion of this substrate for several days, either through low diets in CHO or performing very intense training, followed by a high phase of CHO intake in the three days before the competition (process called super-compensation of glycogen) (Bergström et al., 1972). However, this strategy is somewhat risky and can cause fatigue as a result of training or the low availability of CHO. Years later it was observed that this super-compensation of glycogen can be produced by providing a high amount of CHO during the days before the competition even in the absence of that previous period of discharge, thus avoiding the possible risks (Sherman et al. 1981). And more recently, an interesting study observed that glycogen stores could be optimally recharged in just one day (for example the day before a competition) if the level of physical activity was reduced and a high level of activity was ingested. amount (10 g / kg) of CHO (Bussau et al. 2002). There are also certain nutritional strategies that seem to favor the synthesis of glycogen, especially those that increase gastric emptying, the insulin response or cell osmolarity: that is, those strategies that favor the passage of CHO to the interior of the muscle cell. For example, CHO of high glycemic index or rapid absorption such as glucose could favor the synthesis of glycogen to a greater extent than others of slower absorption such as fructose. In addition, the combination of CHO with protein produces an increase in the insulin response, and its combination with creatine an increase in cellular osmolarity, which would help to further maximize glycogen synthesis (Burke et al. 2017). In summary, to maximize performance it is convenient to reach the competition with full glycogen stores. Ingesting an adequate amount of CHO (> 1 g per kg of weight and hour) after the exercise sessions, preferably in the 2-4 hours after, will help to increase glycogen synthesis. In addition, if rapid recovery is required (such as training or competing twice a day) it is recommended that CHOs have a high glycemic index or rapid absorption such as glucose, and not slow absorption such as fructose. It is also important to increase the intake of CHO the days before the competition and reduce the training load, having shown that leaving the day before the competition break and increase the intake of CHO (10 g / kg) may be sufficient.
REFERENCES
- Bergström J, Hultman E, Roch-Norlund a E (1972) Muscle glycogen synthetase in normal subjects. Basal values, effect of glycogen depletion by exercise and of a carbohydrate-rich diet following exercise. Scand J Clin Lab Invest 29:231–6. doi: 10.3109/00365517209081080
- Burke LM, van Loon LJC, Hawley JA (2017) Postexercise muscle glycogen resynthesis in humans. J Appl Physiol 122:1055–1067. doi: 10.1152/japplphysiol.00860.2016
- Bussau VA, Fairchild TJ, Rao A, et al (2002) Carbohydrate loading in human muscle: An improved 1 day protocol. Eur J Appl Physiol 87:290–295. doi: 10.1007/s00421-002-0621-5
- Ivy JL, Katz AL, Cutler CL, et al (1988) Muscle glycogen synthesis after exercise: effect of time of carbohydrate ingestion. J Appl Physiol 64:1480–1485. doi: 10.1152/jappl.1988.64.4.1480
- Prats C, Helge JW, Nordby P, et al (2009) Dual regulation of muscle glycogen synthase during exercise by activation and compartmentalization. J Biol Chem 284:15692–15700. doi: 10.1074/jbc.M900845200
- Sherman WM, Costill DL, Fink WJ, Miller JM (1981) Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. Int J Sports Med 2:114–8. doi: 10.1055/s-2008-1034594
