Author(s): EOIN RUA ONEILL, J., JOYCE, R., MC LOUGHLIN, N., ROBINSON, J., MC PHILLIPS, C., O CONNELL, B., HORNER, K., Institution: UNIVERSITY COLLEGE DUBLIN, Country: IRELAND, Abstract-ID: 2305

INTRODUCTION:
Best practice guidelines recommend avoiding physical activity for 12-48 hours before RMR testing [1], a challenge for athletes training daily. Recent findings suggest resistance but not aerobic exercise elevates RMR in non-athletes [2]. This study investigates the effect of accustomed exercise on next-day RMR in male endurance athletes, using a randomised crossover design, offering insights for RMR assessment in this population.
METHODS:
Thirteen male endurance athletes undertook rest and exercise conditions in random order one week apart. For the rest condition participants were instructed to perform no exercise for 24 hours before RMR measurement. For the exercise condition they were instructed to undertake a routine steady-state session rated 3-4 on the CR-10 scale [3] on the day prior to RMR measurement. Characteristics of exercise including heart rate were recorded. RMR was measured using a Q-NRG indirect calorimeter, with a within-subject CV of 2.4%±1.6% (range: 0.2%-6%) for day to day reliability based on unpublished data from our lab (n=30) measured following best practice guidelines. In the present study, if participants inter- day CV fell outside this range (>6%), their activities in the preceding 72 hours were further characterised for reasons that may explain a greater variability. Recovery markers were also assessed including blood urea and wellness questionnaire scores [4]. Paired t-tests and Wilcoxon tests compared differences between conditions, CVs assessed inter- day consistency, and Pearsons correlations tested associations between RMR and recovery markers. Significance was set at P<0.05.
RESULTS:
Exercise modalities included 5 undertaking indoor and 4 outdoor cycling, 3 outdoor running, and 1 indoor rowing, with mean (SD) session duration 01:51±01:11 (hh:mm), heart rate 128±16 bpm and RPE score 3.33±0.47. No significant differences were found in post-exercise vs rest RMR (1979±289 vs 1958±251 kcal/day, P=0.74), urea (42±6 vs 39±10 mg/dl, P=0.43), or RQ (0.77 vs 0.78, P=0.62). Wellness scores were lower post-exercise than rest (16.5 vs. 18.8, P=0.03); only sleep quality approached, but did not reach, significant difference (P=0.06). No correlations were observed between recovery markers and RMR changes. Inter-day CVs indicated consistency in RMR between days: 3.8%±3.4%. However, on an individual basis two participants had CVs >6%. Both adhered to guidelines on the day prior to measurement but undertook a high intensity session/competition approximately 48 hours prior.
CONCLUSION:
These findings suggest moderate intensity accustomed endurance exercise may be undertaken on the day prior to RMR measurement without altering results. However, practitioners may need to consider restriction of high intensity exercise in the 48 hours prior to testing. This warrants further study.

[1] S. Fullmer et al. 2015
[2] K. MacKenzie-Shalders et al. 2020
[3] C. Foster et al. 2001
[4] B. D. McLean et al. 2010