Abstract
The pattern of distribution of speed during a running race has been termed ‘pacing’. The pre-exercise diet manipulation is an important factor determining pacing. However, no studies have investigated pacing in younger individuals after pre-exercise diet manipulation. PURPOSE: This study analyzed the pacing displayed by trained young boys during a 10-km run time trial after a 48-h carbohydrate (CHO) diet content manipulation. METHODS: Nineteen trained adolescent boys (13-18 years old) were fed either with their habitual diet (56% CHO) or with high (70% CHO) or low (25% CHO) CHO diets during 48 h. The diets were isocaloric and isoproteic (crossover design). They then performed a 10-km run on an outdoor track. The speed was registered every 400 m and the rating of perceived exertion every 2,000 m. Comparisons were made using one-way ANOVA with repeated measures (P < 0.05). RESULTS: The high-CHO diet led to a greater speed during the last 800 m and a better overall performance compared with the low-CHO diet (12.6 ± 2.2 km.h-1 and 50.0 ± 7.0 min vs 11.7 ± 2.1 km.h-1 and 51.9 ± 8.3 min, respectively, P < 0.05). However, the results for last 800 m and overall performance those fed the high and low CHO diets were not different from those fed the habitual diet (12.0 ± 2.2 km.h-1 and 50.9 ± 7.4 min; P > 0.05). The running speed for the first and last 400 m were higher than the middle 9.200 m section in both low-CHO (13.0 ± 1.9, 13.3 ± 2.7, and 11.8 ± 1.9 km.h-1, respectively) and habitual diet (13.5 ± 1.8, 13.8 ± 2.2, and 11.9 ± 1.9 km.h-1, respectively). However, the running speed in the last 400 m after the high-CHO diet was significantly faster than both the first and middle sections (14.4 ± 2.2, 13.5 ± 2.0, and, 12.1 ± 1.8 km.h-1, respectively). The rating of perceived exertion increased linearly throughout the trial but was slightly higher in the habitual diet compared with the other diets for the first 2,000 m segment (3.7 ± 1.5, 3.1 ± 1.4, and 3.2 ± 1.3 units for habitual, high- and low-CHO diets, respectively). CONCLUSION: A loaded CHO diet induced an increased performance during the final sprint of a 10-km run, thus conferring better overall running performance compared to a low-CHO diet in young boys.
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