Comparison of three type of muscle glycogen loading interventions using a very-high-carbohydrate diet in an elite male racewalker: a case report

Abstract

Purpose: Muscle glycogen storage before a race is necessary for endurance athletes to achieve the best performance. Generally, the recommended carbohydrate intake for preparation over 90 min of the race is 10-12 g·kg--1·day--1. However, it remains unclear whether an elite athlete with an already high-carbohydrate diet can further increase muscle glycogen through a very-high-carbohydrate intake. Therefore, we compared the effects of three types of glycogen loading in a 28-year-old male athlete who belongs to the top 50 racewalkers in the world, consuming a daily energy intake of 4507 kcal and a carbohydrate intake of 12.7 g·kg--1·day--1.

Methods: The racewalker consumed very-high-carbohydrate diets three times for 2 days each, 13.7 g·kg--1·day--1 for trial 1, 13.9 g·kg--1·day--1 for trial 2, and 15.9 g·kg--1·day-1 for trial 3. Muscle glycogen concentrations in the anterior (vastus lateralis and vastus intermedius) and posterior thighs (semimembranosus, semitendinosus, and biceps femoris) were measured using carbon-13 magnetic resonance spectroscopy.

Results: Muscle glycogen concentrations in both the anterior and posterior thighs increased in all trials, particularly in trial 3. Body mass also increased by 1.5 kg in trials 1 and 2 and by 1.8 kg in trial 3 before and after the trials. The participant felt satiated throughout the day and experienced stomach discomfort during trial 3.

Conclusion: We found that a 2-day very-high-carbohydrate diet and tapering of training could further increase the muscle glycogen concentration in athletes. However, we speculated that 15.9 g·kg--1·day--1 carbohy.

Keywords: carbohydrate loading; elite athlete; endurance training; gastrointestinal symptom; glycogen synthesis; track and field.

Figure 1.

Nutritional intervention schedule. Body mass and muscle glycogen were measured pre and post of each trial. Physical activity was recorded during each trial.

Figure 2.

Change in muscle glycogen concentration at the anterior and posterior right thigh. The data of the anterior thigh in (a), and the posterior right thigh in (b). White circle and dashed line express trial 1, gray circle and gray solid line express trial 2, and black triangle and black solid line express trial 3. Change in muscle glycogen concentration in (c). Relative change in muscle glycogen between pre and post in (d). White bar expresses anterior thigh and black bar expresses posterior thigh.

Figure 3.

The time of each physical activity in metabolic equivalents (METs) across the three trials and baseline. Gray bar, slanted line, white bar, and black bar expressed as sedentary (≤1.5 METs), light physical activity (1.5–2.9 METs), moderate physical activity (3.0–5.9), and vigorous physical activity (>6.0 METs), respectively.

Figure 4.

Change in activity energy expenditure per minute through the baseline recording period. The dots represent energy expenditure per minute.

Figure 5.

Change in activity energy expenditure per minute during the three trials. (a) trial 1, (b) trial 2, (c) trial 3. The dots represent the energy expenditure per minute. Gray bar expressed as meal timing (breakfast, lunch, dinner, refuel during the training, and snacks).