Impact of Acute Dietary and Exercise Manipulation on Next-Day RMR Measurements and DXA Body Composition Estimates.

Purpose: The objective of this study is to investigate the effects of acute diet and exercise manipulation on resting metabolic rate (RMR) measurement variability and dual-energy x-ray absorptiometry (DXA) body composition estimates.

Methods: Ten male and 10 female endurance athletes (12 cyclists, 5 triathletes, 4 runners) of tier 2 ( n = 18) to tier 3 ( n = 2) caliber underwent five conditions using a Latin square counterbalance design. For 24 h, athletes consumed a diet providing excessive energy availability (EA) (75 kcal⋅kg fat-free mass (FFM) -1 ) without exercise (GEA rest ), high-EA (45 kcal⋅kg FFM -1 ) without (HEA rest ) or with exercise (HEA ex ), or low-EA (15 kcal⋅kg FFM -1 ) without (LEA rest ) or with exercise (LEA ex ). Exercise involved two bouts of cycling (morning bout: 149 ± 34 min at 55% of maximal aerobic capacity (V̇O 2max ); afternoon bout: 60 min at 65% of V̇O 2max ) that resulted in a cumulative exercise energy expenditure of 30 kcal⋅kg FFM -1 . The following day, RMR and DXA measurements occurred after a 10-h fast and 12-h postexercise.

Results: There were neither sex differences in relative RMR ( P = 0.158) nor effects of any of the five conditions on RMR ( P = 0.358). For both male and female athletes, FFM estimates were decreased following the LEA rest (-0.84 ± 0.66 kg; P = 0.001) and LEA ex (-0.65 ± 0.86 kg; P = 0.016) conditions compared with the GEA rest condition and following the LEA rest (-0.73 ± 0.51 kg; P = 0.001) and LEA ex (-0.54 ± 0.79 kg; P = 0.024) conditions compared with the HEA ex condition. There was no effect of condition on fat mass estimates ( P = 0.819).

Conclusions: Acute periods of diet and exercise manipulation did not create artifacts in next-day RMR measurements. However, as changes in estimates of FFM were seen, diet and exercise should be controlled in the 24-h before DXA scans.