The influence of dietary carbohydrate on performance of supramaximal intermittent exercise

Summary

The present investigation examined the influence of dietary carbohydrate (CHO) on the performance of supramaximal intermittent exercise. A group of 14 moderately trained male students [mean age 21.0 (SD 1.6) years] completed a maximal oxygen consumption test and two identical ‘maximal interval tests’ (MIT, and MIT₂) over a 10-day experimental period. Each MIT involved five 60-s all-out periods of cycling (against 0.736 N · kg⁻¹ body mass), with each period separated by 5 min of passive recovery. All subjects consumed a moderate CHO diet for 3 days preceding MIT₁ (55.3% of energy intake as CHO) and were then randomly assigned to either a high CHO (83%), moderate CHO (58%) or low CHO (12%) diet for the 3 days separating MIT₁ and MIT₂. All food and drink consumed during the experimental period was weighed and recorded for later dietary analysis. Measurements of work done, exercise oxygen consumption ($\dot V$O₂), venous blood pH, plasma lactate and plasma glucose concentrations were compared between interval tests. Independent Student's t-tests revealed that the 5.6% increase in total work done recorded by the high CHO group and the 2.3% increase by the moderate CHO group between MIT₁ and MIT₂, were significantly different to the 5.4% decrease in performance recorded for the low CHO group (P<0.001 and P<0.01, respectively). No significant differences in performance changes was found between the high and moderate CHO groups; 10 subjects in each of these groups would have been necessary to attain significance at the 0.05 level using the same procedures. No changes in $\dot V$O₂, venous blood pH, plasma lactate or glucose concentrations were found among the groups. These data showed that when compared to a low CHO diet, a moderate/high intake of dietary CHO could at least maintain the performance of supramaximal intermittent exercise. The results emphasise the importance of dietary CHO for athletes whose activities involve repeated periods of very high intensity exercise.