Concurrent aerobic exercise interferes with the satellite cell response to acute resistance exercise.

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 affect 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 exercise trials: the RE trial, which consisted of unilateral leg extensions and presses (4 sets ≥ 10 repetitions: 75% 1 repetition maximum, RM); and the AE/CE trial, which included an identical RE protocol with the opposite leg, immediately followed by subjects cycling for 90 min (60% W(max)). 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 with CE (-6 ± 8%). Similarly, MHC I muscle fiber SC density displayed a greater increase following RE (46 ± 14%), compared with 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.