The effect of a high carbohydrate diet on running performance during a 30-km treadmill time trial

SummaryThe purpose of the present study was to examine the influence of a high carbohydrate diet on running performances during a 30-km treadmill time trial. Eighteen runners (12 men and 6 women) took part in this study and completed a 30-km time trial on a level treadmill without modifying their food intake (trial 1). The runners were then randomly assigned to a control or a carbohydrate (CHO) group. The CHO group supplemented their normal diets with additional carbohydrate in the form of confectionery products during the 7 days before trial 2; the control group matched the increased energy intake of the CHO group by consuming additional fat and protein. The mean (SEM) carbohydrate intake of both groups was 334 (22) g before trial 1, after which the CHO group consumed 566 (29) g · day−1 for the first 3 days and 452 (26) g · day−1 for the remaining 4 days of recovery. Although there was no overall difference between the performance times for the two groups during trial 2, the CHO group ran faster during the last 5 km of trial 2 than during trial−1 [3.64 (0.24) m · s−1 vs 3.44 (0.26) m · s−1P < 0.05] . Furthermore, the 6 men in the CHO group ran the 30 km faster after carbohydrate loading [131.0 (5.4) min vs 127.4 (4.9) min;P < 0.05], whereas there was no such improvement in times of the men in the control group. Blood glucose concentrations of both groups decreased below pre-exercise values during trial−1 (P < 0.001), but only the control group had a decrease in blood glucose concentrations during trial 2 (P < 0.001). There were no differences between the concentrations of plasma catecholamines of the control group during the two trials. However, the adrenaline concentrations of the CHO group were lower (P < 0.05) during trial 2 than during trial 1, even though they ran faster during trial 2. These results confirm that dietary carbohydrate loading improves endurance performance during prolonged running and that confectionery can be used as an effective means of supplementing the normal carbohydrate intake in preparation for endurance races.

[1]  R. A. McCance,et al.  The Composition of Foods , 1946 .

[2]  B. Saltin,et al.  Diet, muscle glycogen, and endurance performance. , 1971, Journal of applied physiology.

[3]  T. Reilly,et al.  Exercise: benefits, limits and adaptations. , 1987 .

[4]  Clyde Williams,et al.  The responses of the catecholamines and β-endorphin to brief maximal exercise in man , 2004, European Journal of Applied Physiology and Occupational Physiology.

[5]  K B Pandolf,et al.  Thermoregulatory and blood responses during exercise at graded hypohydration levels. , 1985, Journal of applied physiology.

[6]  C. Willíams,et al.  The influence of high carbohydrate diets on endurance running performance , 2004, European Journal of Applied Physiology and Occupational Physiology.

[7]  E. Coyle.  Timing and method of increased carbohydrate intake to cope with heavy training, competition and recovery. , 1991, Journal of sports sciences.

[8]  Louis Cohen,et al.  Statistics for Social Scientists: An Introductory Text with Computer Programs in Basic , 1982 .

[9]  E. Hultman.  Studies on muscle metabolism of glycogen and active phosphate in man with special reference to exercise and diet. , 1967, Scandinavian journal of clinical and laboratory investigation. Supplementum.

[10]  E Hultman,et al.  Diet, muscle glycogen and physical performance. , 1967, Acta physiologica Scandinavica.

[11]  A. Taylor,et al.  Simple and complex carbohydrate-rich diets and muscle glycogen content of marathon runners , 2004, European Journal of Applied Physiology and Occupational Physiology.

[12]  B. Saltin,et al.  Muscle blood flow and muscle metabolism during exercise and heat stress. , 1990, Journal of applied physiology.

[13]  B. Saltin,et al.  Glycogen utilization in leg muscles of men during level and uphill running. , 1974, Acta physiologica Scandinavica.

[14]  J M Miller,et al.  Effect of Exercise-Diet Manipulation on Muscle Glycogen and Its Subsequent Utilization During Performance* , 1981, International journal of sports medicine.

[15]  R. Maughan.  A simple, rapid method for the determination of glucose, lactate, pyruvate, alanine, 3-hydroxybutyrate and acetoacetate on a single 20-mul blood sample. , 1982, Clinica chimica acta; international journal of clinical chemistry.

[16]  P. Åstrand.  Diet and athletic performance. , 1967, Federation proceedings.

[17]  E Jéquier,et al.  Glycogen storage capacity and de novo lipogenesis during massive carbohydrate overfeeding in man. , 1988, The American journal of clinical nutrition.

[18]  N. Christensen,et al.  The effect of different diets and of insulin on the hormonal response to prolonged exercise. , 1979, Acta physiologica Scandinavica.

[19]  D. Costill,et al.  Calculation of percentage changes in volumes of blood, plasma, and red cells in dehydration. , 1974, Journal of applied physiology.

[20]  R. Maughan.  A simple, rapid method for the determination of glucose, lactate, pyruvate, alanine, 3-hydroxybutyrate and acetoacetate on a single 20-mul blood sample. , 1982, Clinica chimica acta; international journal of clinical chemistry.

[21]  C. Willíams,et al.  Influence of fluid intake on endurance running performance , 2004, European Journal of Applied Physiology and Occupational Physiology.

[22]  J M Miller,et al.  The role of dietary carbohydrates in muscle glycogen resynthesis after strenuous running. , 1981, The American journal of clinical nutrition.