The addition of aerobic exercise (AE) to a resistance exercise (RE) program (concurrent exercise; CE) can interfere with maximum muscle fiber growth achieved with RE. Further, CE appears to markedly affects the growth of myosin heavy chain (MHC) I, but not MHC IIa fibers. The mechanism responsible for this 'interference' is unclear. Satellite cell (SC) responsiveness to exercise appears to influence muscle adaptation, but has not yet been examined following acute concurrent exercise. Thus, we assessed the fiber-type specific SC response to RE, AE, and CE exercise. Eight college-aged males completed the following two trials: RE - unilateral leg-extensions and presses (4 sets ≥ 10 repetitions: 75% 1RM); AE/CE - immediately following an identical RE protocol with the opposite leg, subjects cycled for 90 minutes (60% VO2max). Muscle biopsies were obtained from the vastus lateralis before and 4 days after each session. Samples were cross-sectioned, stained with antibodies against NCAM, Ki-67, and MHC I, counterstained with DAPI, and analyzed for SC density (SC per fiber), SC activation and fiber type. SC density increased to a greater extent following RE (38 ± 10%), compared to CE (-6 ± 8%). Similarly, MHC I muscle fiber SC density displayed a greater increase following RE (46 ± 14%), compared to AE (-7 ± 17%) and CE (-8 ± 8%). Our data indicate that the SC response to RE is blunted when immediately followed by AE, at least in MHC I muscle fibers, and possibly MHC II fibers. This suggests that the physiological environment evoked by AE might attenuate the eventual addition of myonuclei important for maximum muscle fiber growth and consequent force producing capacity.
- Concurrent Exercise
- Myogenic Progenitor Cells
- Copyright © 2012, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology