Self-Regulated Moderate Intensity Habitual Exercise and Next-Day Resting Metabolic Rate in Male Endurance Athletes: Implications for Athlete Testing.

Best practice guidelines for resting metabolic rate (RMR) testing are to avoid moderate to vigorous physical activity for 12-48 h beforehand, the upper limits of which can be difficult for athletes to adhere to. We investigated the effect of self-regulated moderate intensity exercise in a free-living setting on next-day RMR in endurance athletes. Thirteen male endurance athletes participated, alternating between rest and exercise conditions in randomised order. For the exercise condition, participants were instructed to complete a habitual moderate intensity training session (rated 3-4 on the CR-10 rate of perceived exertion scale) on the day before RMR measurement. Recovery markers (blood urea and subjective wellness) were assessed, and intra-individual variation in RMR was explored. Mean (SD) habitual exercise session duration was 111 ± 71 min, heart rate was 128 ± 16 bpm and RPE score was 3.3 ± 0.5. Next-day RMR did not statistically differ between exercise and rest conditions (1979 ± 289 vs. 1958 ± 251 kcal/day, mean Δ = 21 ± 227 kcal/day [95% CI = -116 to 158 kcal/day], p = 0.74, intra-individual inter-day CV 3.8% ± 3.4%). There were no significant correlations between changes in RMR and recovery markers. The findings suggest habitual moderate intensity exercise may be feasible on the day prior to RMR testing in male endurance athletes. Further investigation to perform equivalence testing between conditions is warranted.