Collagen remodeling increases after acute resistance exercise in healthy skeletal muscle irrespective of age

Alterations to the extracellular matrix of skeletal muscle are implicated in age-related declines in muscle quality. Reduced collagen breakdown and collagen accumulation between muscle fibers are suggested to reduce the force-generating capacity of the muscle and impede adaptation to mechanical loading. The current study investigated total intramuscular collagen content in healthy, physical fitness-matched young and older skeletal muscle and how regulators of collagen breakdown respond to an acute bout of resistance exercise. No differences in intramuscular collagen content between young (5.4% ± 2.1) and older muscle (5.1% ± 3.1, <i>P</i> = 0.779) were found. Seventy-two hours after resistance exercise, matrix metalloproteinase (MMP) and tissue inhibitors of metalloproteinase (TIMP) gene expression (<i>MMP2</i>, <i>P</i> = 0.003; <i>MMP9</i>, <i>P</i> ≤ 0.001; <i>MMP14</i>, <i>P</i> = 0.008; <i>TIMP1</i>, <i>P</i> ≤ 0.001), protein content (MMP14 proenzyme, <i>P</i> = 0.016), and protein activity (MMP2, <i>P</i> = 0.009; MMP9, <i>P</i> = 0.014) were elevated in both young and older muscle. An age-by-time interaction was demonstrated 72 h postexercise, with older adults demonstrating more MMP14 enzyme content at this timepoint than young adults (<i>P</i> = 0.02). Main effects of age were demonstrated for <i>MMP2</i> (<i>P</i> = < 0.001), <i>MMP14</i> (<i>P</i> = 0.008), and <i>TIMP2</i> (<i>P</i> ≤ 0.001) gene expression. No significant differences were observed between baseline and 6 h postexercise in either age group. Acute resistance exercise potently stimulates upregulation of markers of collagen breakdown in healthy young and older skeletal muscle. Further research is warranted to determine the precise roles of MMPs and TIMPs in skeletal muscle's response to mechanical loading.<b>NEW & NOTEWORTHY</b> Gene expression, protein content, and protein activity of regulators of collagen breakdown (MMPs and TIMPs) were elevated 72 but not 6 h after an acute bout of resistance exercise in healthy young and older human skeletal muscle, with similar baseline intramuscular collagen content. Young and older adults were healthy and matched for physical fitness, indicating that intramuscular collagen accumulation may be driven by factors other than aging per se.