Impact of Eccentric or Concentric Training on Body Composition and Energy Expenditure

Purpose: To compare the effects of 8-wk eccentric (ECC) versus concentric (CON) training using downhill and uphill running in rats on whole body composition, bone mineral density (BMD), and energy expenditure. Methods: Animals were randomly assigned to one of the following groups: 1) control (CTRL), 2) +15% uphill-running slope (CON), 3) -15% downhill-running slope (ECC15), and 4) -30% downhill-running slope (ECC30). Those programs enabled to achieve conditions of isopower output for CON and ECC15 and of iso-oxygen uptake ((V)over dotO(2)) for CON and ECC30. Trained rats ran 45 min at 15 m.min(-1) five times per week. Total body mass, fat body mass, and lean body mass (LBM) measured through EchoMRI (TM), and 24-h energy expenditure including basal metabolic rate (BMR) assessed using PhenoMaster/LabMaster (TM) cage system were obtained before and after training. At sacrifice, the right femur was collected for bone parameters analysis. Results: Although total body mass increased in all groups over the 8-wk period, almost no change occurred for fat body mass in exercised groups (CON, -4.8 6.18 g; ECC15, 0.6 +/- 3.32 g; ECC30, 2.6 +/- 6.01 g). The gain in LBM was mainly seen for ECC15 (88.9 +/- 6.85 g) and ECC30 (101.6 +/- 11.07 g). ECC was also seen to positively affect BMD. An increase in BMR from baseline was seen in exercise groups (CON, 13.9 +/- 4.13 kJ.d(-1); ECC15, 11.6 +/- 5.10 kJ.d(-1); ECC30, 18.3 +/- 4.33 kJ.d(-1)) but not in CTRL one. This difference disappeared when BMR was normalized for LBM. Conclusions: Results indicate that for iso-(V)over dotO(2) training, the impact on LBM and BMD is enhanced with ECC as compared with CON, and that for isopower but lower (V)over dotO(2) ECC, an important stimulus for adaptation is still observed. This provides further insights for the use of ECC in populations with cardiorespiratory exercise limitations.