Daily Step Count and Postprandial Fat Metabolism.

INTRODUCTION Two benefits of acute exercise are the next day's lowering of the postprandial plasma triglyceride response to a high fat meal and increased fat oxidation. However, if activity levels (daily steps) are very low, these acute adaptations to exercise don't occur. This phenomenon has been termed 'exercise resistance'. This study sought to systematically reduce daily step number and identify the range of step counts that elicit 'exercise resistance'. METHODS Ten participants completed three, five-day trials in a randomized, crossover design with differing levels of step reduction. Following two days of controlled activity, participants completed two days of LOW, LIMITED, or NORMAL steps (2,675 ± 314, 4,759 ± 276, and 8,481 ± 581 steps/day, respectively). Participants completed a 1-hour bout of running on the evening of the second day. High fat tolerance tests were performed on the following morning and postprandial responses were compared. RESULTS Following LOW and LIMITED, postprandial incremental area under the curve (AUC) of plasma triglyceride were elevated 22-23%, compared to NORMAL (p<0.05). Whole body fat oxidation was also significantly lower (16-19%, p<0.05, respectively) in LOW and LIMITED, compared to NORMAL. No significant differences were found between LOW and LIMITED. CONCLUSION Two days of step reduction to approximately 2,500-5,000 steps/day in young healthy individuals impairs the ability of an acute bout of exercise to increase fat oxidation and attenuate postprandial increases in plasma triglycerides. This suggests 'exercise resistance' occurs in individuals taking approximately 5,000 or fewer steps/day while 8,500 steps/day protects against exercise resistance in fat metabolism. It appears that fat metabolism is influenced more by the inhibitory effects of inactivity than by the stimulating effects derived from 1-hour of moderate intensity running.