Respiratory Exchange Ratio: Documented Changes From Seated Rest To Walking

INTRODUCTION: In lab for instruction to show a change in O2 use from sitting to walking, we noticed that across multiple trials, RER (VCO2•VO2 -1) decreased as the participants moved from sitting to walking in the first 2.5 minutes (m). This is opposite of conventional wisdom, teaching, and research in exercise science. The decrease, we hypothesized, could be due to either the enhanced and altered metabolism of walking or the change in posture. In a companion paper, we discounted the effect posture. PURPOSE AND HYPOTHESES: The aim of this research was to document the changes in RER as participants moved from seated rest to walking at 3 mph. We hypothesized that moving from a sustained (7 m) seated position (S) to walking at 3 mph (W) would cause a transient decrease (up to 2 to 4 minutes) in RER after onset of W and then it would rise - just as we have witnessed in the lab over the years. METHODS: We asked 14 participants (9F, 8 M mean age = 22.1 yr), who had fasted for at least 4 hours, to sit on a chair on the treadmill for 25 m to achieve a true resting metabolism. Then they were fitted for gas collection and heart rate. Participants then S for another 7 m, while their ventilated gases and HR data were collected. After this period, participants stood and began to W (3 mph) for another 7 m while ventilated gases and HR continued to be monitored. SUMMARY OF RESULTS: We compared W RERs to end of the 7th minute of S, mean RER = 0.825 (0.128 SD), as the final 2 m of S were virtually identical. RER remained consistent for the first m of W after S and then began to decrease with a most pronounced decrease from 1.5 m to 3 m of W. After that, RER began to approach that of S and remained steady from the 5.5 m to 7 m of W. Statistically, RER in W was different from S at 1.5, 2, 2.5, and 3 m with mean (SD) of 0.7251 (0.105), 0.685 (0.076), 0.713 (0.080), and 0.733 (0.098) with two-tailed p. = 004, .001, .007, and .046, respectively, (from focused contrasts). CONCLUSIONS: The results confirm our hypothesis and reflect our experience in the lab. RER held steady for about a m into W and then it dropped precipitously for 2 m. Then RER returned to the original values seen during S. Assuming RER reflects fat and CHO utilization, then this means that fats are burned relatively readily in the first 2-4 minutes of a walking bout and then CHO becomes more involved as an energy source.