The effects of dietary manipulation upon the respiratory exchange ratio as a predictor of maximum oxygen uptake during fixed term maximal incremental exercise in man.

This study examined the effects of dietary manipulation upon the respiratory exchange ratio (R = VCO2/VO2) as a predictor of maximum oxygen uptake (VO2max). Seven healthy males performed fixed term maximal incremental treadmill exercise after an overnight fast on three separate occasions. The first test took place after the subjects had consumed their normal mixed diet (45 +/- 5% carbohydrate (CHO] for a period of three days. This test protocol was then repeated after three days of a low CHO diet (3 +/- 2% CHO), and again after three days of a high CHO diet (61 +/- 5% CHO). Respiratory gases were continuously monitored during each test using an on-line system. No significant changes in mean exercise oxygen uptake (VO2), VO2max or maximum functional heart rate (FHRmax) were found between tests. Mean exercise carbon dioxide output (VCO2) and R were significantly lower than normal after the low CHO diet (both p less than 0.001) and significantly higher than normal after the high CHO diet (both p less than 0.05). Moreover, compared with the normal CHO diet, the R-time relationship during exercise was at all times significantly (p less than 0.001) shifted to the right after the low CHO diet, and shifted to the left, being significantly so (p less than 0.05) over the final 5 min of exercise, after the high CHO diet.(ABSTRACT TRUNCATED AT 250 WORDS)