Habitual Physical Activity Preserves Energetically Constrained Mitochondrial Programs During Human Skeletal Muscle Aging

Aging is associated with declining aerobic capacity, driven in part by impaired mitochondrial oxidative phosphorylation in skeletal muscle and other tissues. Although prior proteomic studies have demonstrated age-related reductions in mitochondrial proteins, how mitochondrial proteome remodeling is functionally coupled to energetic capacity and modified by habitual physical activity remains poorly understood. We examined the relationships among aging, habitual physical activity, cardiorespiratory fitness, in-vivo mitochondrial oxidative capacity, muscle respirometry, and mitochondrial proteomic profiles across skeletal muscle, PBMCs, naïve CD4⁺ and CD8⁺ T cells, and skin in GESTALT study (healthy 22-89 years old human cohort). Even among individuals who remained healthy into old age, we detected mitochondrial proteome remodeling that was highly selective rather than uniform. Aging preferentially depleted core bioenergetic and proteostatic modules and altered within-pathway protein correlation structure, indicating coordinated mitochondrial network remodeling that was not captured by differential abundance analysis alone. Habitual physical activity and fitness were associated with proteomic signatures that opposed age-related remodeling, particularly within oxidative phosphorylation, mitochondrial translation, and protein import pathways. This rescue signature was strongly linked to skeletal muscle energetic function measured in vivo by 31P magnetic resonance spectroscopy. Individuals with higher physical activity rescue scores exhibited more favorable energetic function across adulthood. Beyond skeletal muscle, aging was associated with coordinated remodeling of mitochondrial proteomic profiles across peripheral tissues, with activity selectively altering tissue-to-tissue mitochondrial correlations rather than a uniform increase in cross-tissue coordination. Mitochondrial proteome remodeling is thus a functionally meaningful axis of human aging and identifies habitual physical activity as a selective modifier of the mitochondrial programs most tightly linked to energetic function.