The effects of dietary manipulation on blood acid-base status and the performance of high intensity exercise

Summary

The effect of a pattern of exercise and dietary modification, which is normally used to alter muscle glycogen content, upon the acid-base status of the blood and the ability to perform high intensity exercise was studied. Eleven healthy male subjects cycled to exhaustion on an electrically braked cycle ergometer at a workload equivalent to 100% of their maximal oxygen uptake ($\dot V_{{\text{O}}_{{\text{ 2 max}}} }$) on three separate occasions. The first exercise test took place after a normal diet (46.2±6.7% carbohydrate (CHO)), and was followed by prolonged exercise to exhaustion to deplete muscle glycogen stores. The second test was performed after three days of a low carbohydrate diet (10.1±6.8% CHO) and subsequently after three days of a high CHO diet (65.5±9.8% CHO) the final test took place. Acid-base status and selected metabolites were measured on arterialised venous blood at rest prior to exercise and during the post-exercise period. Exercise time to exhaustion was longer after the normal (p<0.05) and high (p<0.05) CHO dietary phases compared with the low CHO phase. Resting pre-exercise pH was higher after the high CHO diet (p<0.05) compared with the low CHO diet. Pre-exercise bicarbonate, PCO₂ and base excess measurements were higher after the high CHO treatment compared with both the normal (p<0.01,p<0.05,p<0.01 respectively) and low CHO phases (p<0.001,p<0.01,p<0.001 respectively). Daily dietary acid intake, estimated from food composition tables, was higher than normal during the low CHO diet and lower than normal during the high CHO diet. The present investigation suggests that a predetermined regimen of dietary and exercise variation can significantly affect blood acid-base status and may thereby influence high intensity exercise performance.