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.
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.
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.
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 carbohydrate intake was unrealistic for the actual pre-race diet.
Racewalk events were held at 20 km and 50 km in the Olympics and world championships until 2021 and have been changed to 20 km and 35 km since 2022. As of March 2022, the men’s world record for the 20-km racewalk was held by Suzuki Yusuke, who completed the race at 1:16:36, and that for 50 km was held by Diniz Yohann, who completed it at 3:32:33 [
High-intensity endurance exercise relies on carbohydrates as an energy source [
Herein, we report a case study of carbohydrate loading with a very-high-carbohydrate diet in an elite racewalker who habitually consumed a high-carbohydrate diet to recover from extreme daily training. The racewalker desired to increase his muscle glycogen concentration further to win the race. Therefore, we measured the muscle glycogen concentration (at two sites on his right leg), body mass, and condition, and evaluated the very-high-carbohydrate diet intake to improve his performance.
The athlete was a 28-year-old male who was a 50-km racewalker and belonged to the top 50 in the world, the top 20 in Asia, and the top eight in Japan. His initial height, body mass, and body fat percentage were 172.7 cm, 62.6 kg, and 11.9%, respectively. The athlete provided written informed consent to participate in the study and shared his data in the paper. This study was approved by the Ethics Committee of the Japan Institute of Sports Sciences (approval no. 030, 2020).
The nutritional intervention schedule is shown in
Habitual energy and macronutrient intakes were determined using a self-administered food record with photographs taken 3 days before the 2 weeks of nutritional intervention, including two training days and one off-training day as baseline. Registered dietitians calculated these intakes using the original software, according to the Standard Tables of Food Composition in Japan 2020 (Mellon II; SOFTOM Co., Ltd, Tokyo, Japan).
Physical activity throughout the trials and baseline period was recorded using a triaxial accelerometer (Active Style Pro HJA-750C; Omron Healthcare Co., Ltd, Kyoto, Japan). The athlete was asked to wear the device on his waist during all activities, except bathing and dressing. There was no training in water. The physical activity intensity thresholds were defined as follows: sedentary, ≤1.5 metabolic equivalents (METs); light physical activity (LPA), 1.5–2.9 METs; moderate physical activity (MPA), 3.0–5.9 METs; and vigorous physical activity (VPA), ≥6.0 METs [
Body mass, impedance, and muscle glycogen concentration were measured after breakfast on days 1 (pre) and 3 (post) (
Muscle glycogen concentrations were measured with carbon-13 magnetic resonance spectroscopy using a 3-T superconducting magnetic resonance (MR) scanner (Magnetom Verio, Siemens Co., Ltd, Erlangen, Germany) for the anterior thigh (vastus lateralis and vastus intermedius), which constitutes half of the thigh length, and a similar MR scanner (Magnetom Skyra, Siemens Co., Ltd) for the posterior thigh (semimembranosus, semitendinosus, and biceps femoris), which spans proximally a third of the thigh length. The athlete lay on his back for measurement and fixed his right leg on a 13C-1H double-tuned surface coil. The 13C-glycogen signal was obtained as the sum of 4500 scans with a repetition time of 200 ms. Muscle glycogen concentration was calculated using a glycogen cylindrical phantom of known concentration (120 mM glycogen from oysters and 50 mM KCL)11. The coefficient of variation of repeated measurements of muscle glycogen concentration using this method with repositioning and reshimming was 3.5% in individuals in the previous study [
The initial body mass was 63.0, 62.4, and 62.8 kg at trials 1, 2, and 3, respectively. Body mass increased after the 2-day glycogen loading period in all trials, and the increase in trial 3 was greater than that in the other trials (
The training menu for three-day baseline period consisted of the following components: AM, stretching, warming-up (12.50 min·km-1 × 1.2 km), interval training (2 km × 3 times + 200 m × 5 times), cooling-down; PM, stretching, weight training, racewalking (5.50 min·km-1 × 14 km) during day 1; AM, Rest; PM, stretching, racewalking (6.00 min·km-1 × 10 km), technical practice (drill); Night, technical practice (swinging arms), bodyweight workout during day 2; AM, stretching, racewalking (6.00 min·km-1 × 10 km), technical practice (drill); PM, long distance racewalking (4.96 min·km-1 × 25 km) during day 3. The training menus used during the three trials are listed in
We also obtained the following subjective findings through interviews after the athlete underwent the three trials (
In this case report, we compared three strategies of muscle glycogen loading in an elite athlete who had already been consuming a carbohydrate diet higher than recommended (12.7 g·kg-1·day-1). To our knowledge, this is the first case report to show that a very-high-carbohydrate diet (15.9 g·kg-1·day-1) in combination with tapering of training was beneficial for increasing muscle glycogen concentration. However, we considered that the very-high-carbohydrate diet in trial 3 was too high to be used in an actual race.
The differences in the changes in muscle glycogen concentrations in the anterior and posterior thigh muscles during the three trials were not the same. However, the change in the sum of muscle glycogen concentration and body mass was greater in trial 3 than in the other trials. Furthermore, the total body water increased and the impedance values in all body regions decreased with changes in muscle glycogen concentration. The impedance at a frequency of 50 kHz represents the total body water resistivity [
To maximize muscle glycogen concentration, athletes and coaches must consider training volume and intensity prior to the race. In this study, the training volume and intensity decreased during the three trials to imitate tapering during the pre-race period (
The amounts of energy and carbohydrates in trials 1 and 2 were similar. Nevertheless, the increase in muscle glycogen in trial 2 was greater than that in trial 1. One of the reasons for this phenomenon might be the amount of carbohydrate per meal or snack, because intestinal carbohydrate digestion and absorption rates are limited [
Muscle glycogen utilization is affected by the movements performed in sports and the muscle groups involved [
A limitation of the present study is that the effects of a very-high-carbohydrate diet could only be evaluated based on changes in muscle glycogen. Therefore, future studies should assess the relationship between exercise performance and physiological parameters such as muscle and liver glycogen, blood glucose, insulin, glucagon, and lactate levels to better understand their effects. Moreover, we were not able to completely control the food intake and training volume before each trial, and the difference in the muscle glycogen concentration pre-among these three trials, especially trial 3, may have affected the muscle glycogen concentration. Finally, this study was conducted on only one elite athlete; therefore, further studies involving more elite racewalkers are required to validate our findings. In the future, a crossover randomized controlled trial with a large sample size and further studies on the effects of different exercise intensities during tapering on muscle glycogen accumulation are required.
In conclusion, we report a case study in which an elite race walker who regularly consumed a high-carbohydrate diet showed an increase in muscle glycogen concentration following a very-high-carbohydrate diet. Our findings from this unique case could be helpful to athletes who consume a high-carbohydrate diet and serve as a basis for future studies on this topic. However, it is important to note that our data were obtained from a single elite athlete. Additional studies are required to establish the effects of carbohydrate-loading strategies on racewalk performance and to develop stronger evidence.
The authors wish to thank the athlete who participated in this study. We are also grateful to Akiko Uchizawa for analyzing energy expenditure. This case study was supported by JSPS KAKENHI Grant-in-Aid for Scientific Research Grant No.19H04017. Furthermore, this data analysis and publication were supported by JSPS KAKENHI Grant in Aid for JSPS Fellows Grant No. 21J00492.
Nutritional intervention schedule.
Body mass and muscle glycogen were measured pre and post of each trial. Physical activity was recorded during each trial.
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.
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.
Change in activity energy expenditure per minute through the baseline recording period.
The dots represent energy expenditure per minute.
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).
Menu of test meals and snacks during each trial.
Trial 1 | Trial 2 | Trial 3 | |
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Day 1 |
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Breakfast | 2 rice balls, Dorayaki, Castilla, Mitarashi dango, Fruits jelly, Yogurt, Orange juice | 2 rice balls, Castilla, Fruits jelly, Yogurt, Orange juice | 2 rice balls, Castilla, Fruits jelly, Yogurt, Orange juice |
During training | Sport drink, Sport gel | Sport drink, Sport gel | Sport drink, Sport gel |
Lunch | Steamed white rice (250 g), Spaghetti with mushroom soy sauce, Fried pork and vegetables with lemon soy sauce, Burdock and radish simmered in soy sauce, Right boiled bok choy, Tomato soup, Fruits, Yogurt, Low fat milk, Small pancake with honey | Steamed white rice (250 g), La France jelly, Spaghetti with cabbage and anchovy, Pork and vegetables simmered in sansho sauce, Radish and satsuma-age simmered in soy sauce, Right boiled moroheiya, Pumpkin pottage, Fruits, Orange juice, Yogurt, Low fat milk | Steamed white rice (350 g), Soba with boiled beef, Spaghetti with tomato sauce, Orange juice, Yogurt with honey, Lychee jelly, Laminaria boiled in sweetened soy sauce |
During training | Sport drink | Sport drink | Sport drink |
Snacks | Dorayaki, Mitarashi dango | Dorayaki, Mitarashi dango, Yo-kan | |
Dinner | Steamed white rice (300 g), Udon noodles, Chicken wings and eggs simmered in soy sauce, Komatsuna dressed with mustard, Pumpkin and sweet potato gratin, Fruits, Orange juice, Yogurt with honey, Natto, Steamed bread, Salted plum, Laminaria boiled in sweetened soy sauce | Steamed white rice (300 g), Hiyamugi noodle, Simmered flounder, Natto, Fruits, Orange juice, Right boiled komatsuna and enoki with dressing, Yogurt with honey, Low fat milk, Rice-flour dumpling with soybean flour, Salted plum, Laminaria boiled in sweetened soy sauce | Steamed white rice (350 g), Spaghetti with tuna and broccoli, Rice cake and lotus root simmered in soy sauce, Orange juice, Yogurt with honey, Low fat milk, Strawberry ice cream, Laminaria boiled in sweetened soy sauce |
Breakfast | 2 rice balls, Dorayaki, Castilla, Mitarashi dango, Fruits jelly, Yogurt, Orange juice | 2 rice ball, Castilla, Fruits jelly, Yogurt, Orange juice | 2 rice ball, Castilla, Fruit jelly, Yogurt, Orange juice |
During training | Sport drink, Sport gel | Sport drink, Sport gel | Sport drink |
Lunch | Steamed white rice (250 g), Tanuki soba, Grilled pork with mustard sauce, Potato simmered in soy sauce, Miso soup, Fruits, Orange juice, Yogurt | Steamed white rice (250 g), Soba with boiled beef, Steamed chicken with lemon sauce, Marinated squid and cucumber, Simmered komatsuna in soy cause base broth, Fruits, Low fat milk, Yogurt, Pancake with honey | Steamed white rice (350 g), Udon noodle topped with starchy sauce, Sardine ball simmered in soy sauce, Orange juice, Yogurt with honey, Low fat milk, Laminaria boiled in sweetened soy sauce |
During training | Sport drink | Sport drink | Sport drink |
Snacks | Dorayaki, Mitarashi dango | Sport gel, Dorayaki, Mitarashi dango, Yokan | |
Dinner | Steamed white rice (300 g), Somen noodles, Boiled egg, Pork and cabbage simmered in consomme, Butterbur and freeze-dried tofu simmered in soy sauce, Boiled spinach with enoki mushroom sauce, Chicken, tofu, komatsuna, and radish in soup, Yogurt with honey, Low fat milk, Fruits, Orange juice, Mizu yokan, Salted plum, Laminaria boiled in sweetened soy sauce | Steamed white rice (300g), Spaghetti with tuna and soy sauce, Grilled salmon, Boiled green beans with sesame, Soybeans and vegetables simmered in soy sauce, Miso soup, Fruits, Orange juice, Low fat milk, Yogurt, Almond jelly, Salted plum, Laminaria boiled in sweetened soy sauce | Steamed white rice (350 g), Somen noodles, Stew with chicken and turnip, Orange juice, Yogurt with honey, Sesame dumplings, Laminaria boiled in sweetened soy sauce |
Breakfast | 2 rice ball, Dorayaki, Castilla, Mitarashi dango, Fruits jelly, Yogurt, Orange juice | 2 rice balls, Castilla, Fruits jelly, Yogurt, Orange juice | 2 rice balls Castilla, Fruits jelly, Yogurt, Orange juice |
Energy and macronutrient intakes.
Baseline | Trial 1 | Trial 2 | Trial 3 | ||
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Breakfast | |||||
Energy | (kcal·d-1) | 822 ± 45 | 1192 ± 0 | 797 ± 0 | 797 ± 0 |
Protein | (g·d-1) | 27 ± 6 | 27 ± 0 | 20 ± 0 | 20 ± 0 |
Fat | (g·d-1) | 18 ± 11 | 7 ± 0 | 5 ± 0 | 5 ± 0 |
Carbohydrate | (g·d-1) | 141 ± 40 | 259 ± 0 | 173 ± 0 | 173 ± 0 |
Lunch | |||||
Energy | (kcal·d-1) | 828 ± 192 | 1304 ± 49 | 1460 ± 40 | 1599 ± 173 |
Protein | (g·d-1) | 27 ± 7 | 50 ± 4 | 63 ± 10 | 44 ± 10 |
Fat | (g·d-1) | 17 ± 9 | 21 ± 1 | 22 ± 5 | 12 ± 5 |
Carbohydrate | (g·d-1) | 138 ± 23 | 226 ± 10 | 251 ± 7 | 323 ± 23 |
Dinner | |||||
Energy | (kcal·d-1) | 1566 ± 193 | 1672 ± 39 | 1490 ± 101 | 1562 ± 250 |
Protein | (g·d-1) | 56 ± 2 | 67 ± 12 | 61 ± 1 | 41 ± 6 |
Fat | (g·d-1) | 40 ± 5 | 28 ± 7 | 24 ± 15 | 21 ± 5 |
Carbohydrate | (g·d-1) | 243 ± 39 | 282 ± 12 | 252 ± 10 | 296 ± 45 |
During training | |||||
Energy | (kcal·d-1) | 615 ± 440 | 250 ± 0 | 250 ± 0 | 250 ± 0 |
Protein | (g·d-1) | 3 ± 3 | 0 ± 0 | 0 ± 0 | 0 ± 0 |
Fat | (g·d-1) | 0 ± 0 | 0 ± 0 | 0 ± 0 | 0 ± 0 |
Carbohydrate | (g·d-1) | 151 ± 108 | 62 ± 0 | 62 ± 0 | 62 ± 0 |
Snacks | |||||
Energy | (kcal·d-1) | 676 ± 130 | 200 ± 0 | 595 ± 0 | 746 ± 0 |
Protein | (g·d-1) | 23 ± 4 | 8 ± 0 | 16 ± 0 | 17 ± 0 |
Fat | (g·d-1) | 12 ± 9 | 4 ± 0 | 7 ± 0 | 7 ± 0 |
Carbohydrate | (g·d-1) | 123 ± 48 | 33 ± 0 | 120 ± 0 | 157 ± 0 |
Total | |||||
Energy | (kcal·d-1) | 4507 ± 570 | 4617 ± 10 | 4591 ± 61 | 4954 ± 77 |
Protein | (g·d-1) | 136 ± 8 | 152 ± 8 | 159 ± 11 | 122 ± 4 |
(g·kgBM-1·d-1) | 2.2 ± 0.1 | 2.3 ± 0.1 | 2.5 ± 0.2 | 2.0 ± 0.1 | |
Fat | (g·d-1) | 87 ± 30 | 60 ± 6 | 57 ± 10 | 45 ± 0 |
Carbohydrate | (g·d-1) | 796 ± 160 | 862 ± 3 | 857 ± 17 | 1010 ± 21 |
(g·kgBM-1·d-1) | 12.7 ± 2.5 | 13.7 ± 0.0 | 13.9 ± 0.3 | 15.9 ± 0.3 |
Body mass, total body water and impedance values.
Trial 1 |
Trial 2 |
Trial 3 |
|||||||
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Pre | Post | Change | Pre | Post | Change | Pre | Post | Change | |
Body mass (kg) | 63.0 | 64.5 | 1.5 | 62.4 | 63.9 | 1.5 | 62.8 | 64.6 | 1.8 |
Total body water (kg) | 40.7 | 41.5 | 0.8 | 40.5 | 41.4 | 0.9 | 41.3 | 42.4 | 1.1 |
Impedance Z value | |||||||||
Right arm (Ω) | 297.3 | 288.4 | -8.9 | 299.9 | 296.5 | -3.4 | 303.3 | 284.4 | -18.9 |
Left arm (Ω) | 309.4 | 295.0 | -14.4 | 304.6 | 295.6 | -9.0 | 312.4 | 286.4 | -26.0 |
Trunk (Ω) | 22.4 | 21.9 | -0.5 | 22.5 | 21.9 | -0.6 | 22.3 | 21.1 | -1.2 |
Right leg (Ω) | 224.6 | 217.1 | -7.5 | 227.5 | 213.0 | -14.5 | 231 | 216.4 | -14.6 |
Left leg (Ω) | 217.8 | 215.6 | -2.2 | 225.8 | 208.6 | -17.2 | 231.1 | 211.6 | -19.5 |
Training menu during three trials.
Trial 1 | Trial 2 Day1 | Trial 3 | |
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Day1 |
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AM | Stretching | Stretching | Stretching |
Treadmill walking (7 km; 6.00 min·km-1) | Treadmill walking (7 km; 5.77 min·km-1) | Treadmill walking (7 km; 5.73 min·km-1) | |
Stretching | |||
PM | Stretching | Stretching | Stretching |
Treadmill walking (5 km; 6.00 min·km-1) | Treadmill walking (5 km; 6.00 min·km-1) | Treadmill walking (5 km; 6.00 min·km-1) | |
Stretching | |||
AM | Stretching | Stretching | Stretching |
Treadmill walking (6 km; 5.50 min·km-1) | Treadmill walking (6 km; 5.43 min·km-1) | Treadmill walking (2 km; 5.43 min·km-1) | |
Stretching | Technical practice (swinging arms) | ||
PM | Rest | Rest | Rest |
Summary of the subjective comments in this elite racewalker.
Subjective comments | |
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Trial 1 | The athlete was filled with a fullness after the breakfast. |
Trial 2 | The athlete did not feel any gastrointestinal discomfort through the trial. |
Trial 3 | The athlete was filled with a fullness and experienced stomach discomfort throughout the day. |