Nutritional influences on endurance running performance in man

2012-11-26T13:54:21Z (GMT) by Moya P.D. Walker
The overall aim of this thesis was to examine the influence of nutritional modifications of the normal diet, on endurance running performance. There is considerable evidence demonstrating that a high carbohydrate (CHO) diet in the days prior to exercise can significantly increase the endurance capacity of cycle ergometry. However, there is limited evidence to show that endurance running performance is also enhanced by a high CHO diet. Thus the first study presented in this thesis examined the influence of a high CHO diet on endurance running performance over a distance of 30km. Subjects (n=18) attempted to complete two 30km runs on a motorised treadmill as fast as possible, 7 days apart. Prior to Run 1 all individuals consumed their prescribed normal diet, whereas after Run 1, the normal diet was supplemented with either high CHO confectionery products for the Carbohydrate group (n=9), or additional fat and protein for the Control group (n=9). There were no significant improvements in the performance time for the individuals in the CHO group, although they achieved a 1.91 improvement compared to a 0.21 decrement in performance time for the Control group. However, the high CHO group demonstrated significantly higher running speeds over the last 5km (p(O.OOI), as well as significantly higher respiratory exchange ratios and blood glucose concentrations over the final 10km. To examine the influence of CHO ingestion dur-ing endurance exercise, trained individuals (n=15) ran two simulated races on a motorised treadmill, 7 days apart. The subjects aimed to cover as much distance as possible within two hours, whilst ingesting either a CHO supplement or a Placebo. Seven days later subjects repeated the run whilst ingesting the fluid not ingested ,on Run I. Although there were no significant differences in'the distances covered, the CHO run showed significantly higher running speeds towards the end of the run (p(0.05), with significantly higher blood glucose concentrations during the last 30 min of exercise. Fat metabolism was noticeably suppressed with a concomitant increase in CHO oxidation. The final study attempted to enhance free fatty acid oxidation (FFA) by increasing carnitine availability, the transporter of FFA into the mitochondria. Subjects (n=14) completed two endurance capacity runs to exhaustion at 70 IVO. max, 3 weeks apart. During the 3 week interim period, half the individuals supplemented their diet with a carnitine supplement, whilst the others supplemented their diet with a placebo. There was no significant improvement in the run time to exhaustion after carnitine supplementation. However, there were significantly lower R values and blood glucose concentrations at exhaustion for the carnitine group, suggesting an increase in fat metabolism with a concurrent reduction in CHO utilisation. Thus certain nutritional modifications of the normal diet may enhance endurance running performance in man.