Resistance training generally increases skeletal muscle
hypertrophy, whereas aging is associated with a loss in muscle mass. Interestingly, select studies suggest that aging, as well as
resistance training, may lead to a reduction in the abundance of skeletal muscle myofibrillar (or
contractile) protein (per mg tissue). Proteomic interrogations have also demonstrated that aging, as well as weeks to months of
resistance training, lead to appreciable alterations in the muscle
proteome. Given this evidence, the purpose of this small pilot study was to examine total myofibrillar as well as total sarcoplasmic
protein concentrations (per mg wet muscle) from the vastus lateralis muscle of males who were younger and resistance-trained (denoted as YT, n = 6, 25 ± 4 years old, 10 ± 3 self-reported years of training), younger and untrained (denoted as YU, n = 6, 21 ± 1 years old), and older and untrained (denoted as OU, n = 6, 62 ± 8 years old). The relative abundances of actin and
myosin heavy chain (per mg tissue) were also examined using SDS-PAGE and Coomassie staining, and shotgun proteomics was used to interrogate the abundances of individual sarcoplasmic and myofibrillar
proteins between cohorts. Whole-body fat-free mass (YT > YU = OU), VL thickness (YT > YU = OU), and leg extensor peak torque (YT > YU = OU) differed between groups (p < 0.05). Total myofibrillar
protein concentrations were greater in YT versus OU (p = 0.005), but were not different between YT versus YU (p = 0.325). The abundances of actin and
myosin heavy chain were greater in YT versus YU (p < 0.05) and OU (p < 0.001). Total sarcoplasmic
protein concentrations were not different between groups. While proteomics indicated that marginal differences existed for individual myofibrillar and sarcoplasmic
proteins between YT versus other groups, age-related differences were more prominent for myofibrillar
proteins (YT = YU > OU, p < 0.05: 7
proteins; OU > YT = YU, p < 0.05: 11
proteins) and sarcoplasmic
proteins (YT = YU > OU, p < 0.05: 8
proteins; OU > YT&YU, p < 0.05: 29
proteins). In summary, our data suggest that modest (~9%) myofibrillar
protein packing (on a per mg muscle basis) was evident in the YT group. This study also provides further evidence to suggest that notable skeletal muscle
proteome differences exist between younger and older humans. However, given that our n-sizes are low, these results only provide a preliminary phenotyping of the reported
protein and proteomic variables.