Robinson, Matthew

There is evidence that the anabolic response to exercise is blunted in skeletal muscle in older adults. Older adults also exhibit reduced mitochondrial content and lower oxidative capacity. Since mitochondria provide chemical energy for muscle protein synthesis, it is possible that age‐related changes to mitochondrial physiology may contribute to anabolic resistance. We evaluated this possibility by measuring mitochondrial function and anabolic responses to exercise in 12 young (19–34 yrs) and 12 older (67–83 yrs) adults. Serial vastus lateralis biopsies were collected during an infusion of 13 C 6 phenylalanine to measure muscle protein synthesis at baseline and 16 hours after a single bout of unaccustomed resistance exercise (unilateral knee extension, 8 sets, 10 repetitions at 70% of 1‐repetition maximum). Real‐time PCR and RNA sequencing were used to evaluate the transcriptional response to acute exercise in muscle tissue. Respiratory capacity of isolated mitochondria was measured by high‐resolution respirometry. Mitochondrial respiratory capacity was significantly lower in older adults (4.67±0.47 pmol/s/ug) compared to young (6.60±0.70 pmol/s/ug, p=0.024). Postabsorptive protein synthesis rates were similar in young and old for mixed muscle (Y: 0.067±0.005 %/hr, O: 0.104±0.030 %/hr, p=0.13), mitochondrial (Y: 0.076±0.014 %/hr, O: 0.089±0.017 %/hr, p=0.58), and myofibrillar fractions (Y: 0.073±0.005 %/hr, O: 0.072±0.015 %/hr, p=0.94). Exercise increased protein synthesis similarly in young and old for mixed muscle (Fold changes Y: 1.45±0.16, O: 1.46±0.18, p=0.98), mitochondrial (Y: 0.90±0.28, O: 1.74±0.41, p=0.11), and myofibrillar (Y: 1.35±0.13, O: 1.37±0.18, p=0.93). These data demonstrate older adults have lower mitochondrial respiratory capacity yet exhibit similar anabolic responses to resistance exercise compared to young. Protein synthesis does not appear limited by the decreased mitochondrial capacity with age.