Purpose: This study aimed to investigate the effects of a 6-month preventive resistance training program on resting metabolic rate (RMR) and its associations with fat-free mass (FFM) and the newly described myokine irisin as two potential mechanistic links between exercise training and RMR.
Methods: In a randomized controlled trial, 74 sedentary healthy male and female participants either completed 6 months of high-repetition resistance training 3 d·wk−1 in accordance with the American College of Sports Medicine recommendations (RT: n = 37; 47 ± 7 yr; body mass index, 25.0 ± 3.4 kg·m−2) or served as controls (CO: n = 37; 50 ± 7 yr; body mass index, 24.2 ± 3.2 kg·m−2). Strength (one-repetition maximum), RMR (indirect calorimetry), body fat (caliper method), and serum irisin concentration (enzyme-linked immunosorbent assay) were measured before and after 6 months of training.
Results: Training led to an increase in strength (one-repetition maximum leg press, 16% ± 7%; P < 0.001). RMR increased in RT (1671 ± 356 vs 1843 ± 385 kcal·d−1, P < 0.001) but not in CO (1587 ± 285 vs 1602 ± 294 kcal·d−1, P = 0.97; group–time interaction, P < 0.01). Body weight (RT, −0.5 ± 2.4 kg; CO, 0.1 ± 2.3 kg), body fat percentage (RT, −1.1% ± 2.5%; CO, −0.7% ± 2.9%), and FFM (RT, 0.4 ± 2.1 kg; CO, 0.6 ± 1.9 kg) did not develop differently between groups (group–time interaction: P = 0.29, P = 0.54, and P = 0.59, respectively). Serum irisin concentration increased in CO (70.8 ± 83.4 ng·mL−1, P < 0.001) but not in RT (22.4 ± 92.6 ng·mL−1, P = 0.67; group–time interaction, P < 0.01). The change in RMR was not associated with the change in FFM (r = −0.11, P = 0.36) or irisin (r = −0.004, P = 0.97).
Conclusions: Preventive resistance training elicits an increase in RMR. However, in contrast to currently discussed hypotheses, this increase does not seem to be mediated by training-induced changes in FFM or circulating irisin concentration, which casts doubt in the meaning of irisin for human energy balance.
1Department of Medical Oncology, National Center for Tumor Diseases (NCT), Heidelberg University Hospital, Heidelberg, GERMANY; 2German University of Applied Sciences for Prevention and Health Management, Saarbrücken, GERMANY; 3Institute of Sports and Preventive Medicine, Saarland University, Saarbrücken, GERMANY; and 4Institute for Molecular Cell Biology, Saarland University, Homburg, GERMANY
Address for correspondence: Friederike Scharhag-Rosenberger, Ph.D., National Center for Tumor Diseases (NCT), Department of Medical Oncology, Im Neuenheimer Feld 460, 69120 Heidelberg, Germany; E-mail: email@example.com.
Submitted for publication September 2013.
Accepted for publication January 2014.