Impact of acute dietary and exercise manipulation on next day RMR measurements and DXA body composition estimates.

Purpose: 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: 10 male and 10 female endurance athletes (12 cyclists, 5 triathletes, 4 runners) of Tier 2 (n = 18) to Tier 3 (n = 2) calibre underwent five conditions using a Latin square counterbalance design. For 24 hours, athletes consumed a diet providing excessive energy availability (75 kcal‧kg fat free mass (FFM) -1 ) without exercise (GEA rest ), high energy availability (45 kcal‧kg FFM -1 ) without (HEA rest ) or with exercise (HEA ex ), or low-energy availability (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 (VO 2 max); afternoon bout: 60 min at 65% of VO 2 max) 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-hour fast and 12-hours post-exercise.

Results: There were no 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 to 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 to the HEA ex condition. There was no effect of condition on fat mass estimates ( p = 0.819).

Conclusion: 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-hours prior to DXA scans.