Regional Differences In Mitochondrial Adaptations After Eccentric Resistance Training In Old Men

PURPOSE: Resistance training (RT) prevents muscle atrophy and preserves muscle function in aging while eliciting sufficient metabolic demands to alter mitochondrial homeostasis in old adults. Eccentric RT (ECC-RT) was suggested as a valid alternative to classic RT in the elderly, requiring less effort and energy expenditure. However, it may exert potential negative effects on mitochondrial adaptations, limiting the recovery of oxidative function in this specific population. We then investigated mitochondrial adaptations in response to ECC-RT in old adults and whether those changes were regionally different as previously showed for muscle hypertrophy and mechano-transduction. METHODS: Eight subjects (67 ± 1.3 yr) underwent 8 weeks of ECC-RT consisting of 4 sets of 15 repetitions at 60% of ECC 1RM, 3 times/week. Before and after the intervention, knee extensors' maximal voluntary isometric contraction (MVIC) torque was assessed at 3 joint angles (60°, 70°, 80°). Muscle volume (QV) was measured by MRI. Muscle biopsies were collected from Vastus Lateralis both at mid-belly (M) and in proximity to the distal myotendinous junction (D). Markers of mitochondrial biogenesis, content and dynamics were analyzed by western blot. RESULTS: After intervention, both MVIC torque and QV increased (+17% and + 4% respectively, p < .05). PGC-1α decreased in M (-39%, p < .05) and not in D (+2%, p > .05). TOM20 and CS decreased in M (-23% and -31% respectively, p < .05) and did not change in D (+5% and + 4% respectively, p > .05). Phosphorylated DRP1 increased in M (+104%, p < .01) and not in D (+9%, p > .05). MFN1 did not change in either M (-5%, p > .05) or D (-9%, p > .05). No changes were observed for OPA1 in either M (-6%, p > .05) or D (+7%, p > .05). CONCLUSIONS: ECC-RT dampened mitochondrial biogenesis, reduced mitochondrial content, and induced fission at the mid-belly site of Vastus Lateralis muscle. These adaptations were not observed at the distal site, which has been previously shown to be the more mechano-sensitive in response to ECC-RT in younger adults. We hypothesize that a lower strain applied at the mid-belly site may have induced smaller metabolic perturbations, therefore resulting in regionally different mitochondrial adaptations. Thus, studies investigating skeletal muscle plasticity should consider site-specific adaptations. This project was supported by the BBSRC [Grant no. BB/K019104/1] and by the UK MRC (Grant no. MR/P021220/1) as part of the MRC-ARUK Centre for Musculoskeletal Aging Research awarded to the Universities of Nottingham and Birmingham and supported by the National Institute of Health Research (NIHR) Not