Early myogenic responses to acute exercise before and after resistance training in young men

Abstract

To enable dynamic regulation of muscle mass and myofiber repair following injury, a satellite cell precursor population exists to supply additional nuclei. Activated satellite cells express many genes and associated proteins necessary for maturation and incorporation into the damaged fiber. There is little knowledge about the response of these markers following whole-body resistance exercise training. We investigated the impact of 12 weeks of progressive whole-body resistance training on the expression of MRFs, PAX7, NCAM, and FA1, incorporating both acute and chronic resistance exercise components. Ten young recreationally active males (21.2 ± 3.5 years) performed 12 weeks of whole-body resistance training at 70-85% of their predetermined one-repetition maximum (1RM). At the initiation and completion of the training period, muscular strength was assessed by RM and dynamometer testing, and vastus lateralis samples were obtained prior to and 3 h following an acute resistance exercise test (both whole-body and isometric exercises). Increased mRNA expression of PAX7 (threefold), NCAM (threefold), MYF5 (threefold), MYOD (threefold) and MYOGENIN (twofold) was observed 3 h after the acute resistance exercise test, both pre and posttraining. Similarly, PAX7 (11-fold) and FA1 (twofold) protein abundance increased after acute exercise, while resting NCAM (eightfold) and FA1 (threefold) protein abundance increased following 12 weeks of resistance training. It is possible that these molecular changes are primarily due to the preceding exercise bout, and are not modified by long-term or whole-body exercise training.

Keywords: Acute exercise; myogenic regulatory factors; resistance exercise training.

Figure 1

mRNA and protein expression of markers associated with satellite cell activation change following acute resistance exercise, irrespective of training. mRNA and protein expression of PAX7 (A, C) and NCAM (B, D) were measured before and after 12 weeks of resistance training. Open bars (□) represent resting; closed bars (▪) represent 3 h postexercise. mRNA values were normalized to GAPDH and protein to Actin, representing the mean ± SEM of 10 young men. All values are presented as fold change, normalized to pretraining baseline values. The sum of both phosphorylated NCAM bands was taken. *denotes statistical significant effect for an acute resistance exercise bout (P < 0.05), **P < 0.01. ^‡denotes a statistically significant training effect between pre- and posttraining (P < 0.05).

Figure 2

Myogenic regulatory factors responsible for satellite cell activation, proliferation and differentiation are significantly increased in response to acute resistance exercise, but not influenced by training. mRNA expression of MRFs MYF5, MYOD, and MYOGENIN were measured before and after 12 weeks of resistance training. Open bars (□) represent resting; closed bars (▪) represent 3 h postexercise. mRNA values were normalized to GAPDH, representing the mean ± SEM of 10 young men. All values are presented as fold change, normalized to pretraining baseline values. **denotes statistical significant effect for an acute resistance exercise bout (P < 0.01), ***P < 0.001.

Figure 3

Following acute resistance exercise and training there are changes in the expression of FA1, a marker of satellite cells with regenerative potential. mRNA and protein expression of FA1 (A, B) were measured before and after 12 weeks of resistance training. Open bars (□) represent resting; closed bars (▪) represent 3 h post-exercise. mRNA values were normalized to GAPDH and protein to Actin, representing the mean ± SEM of 10 young men. All values are presented as fold change, normalized to pretraining baseline values. ^‡‡‡denotes a statistically significant training effect between pre- and posttraining (P < 0.001).