MUSCLE STRENGTH WITH AGING

Abstract

PURPOSE: This study compared muscle quality (strength/unit size) at the whole muscle and myocellular level with aging. METHODS: Whole muscle testing of the quadriceps femoris muscle was completed on 20 young (25 ± 3y) and 22 old (78 ± 6y) sedentary men and women to determine maximal isometric force (Po) and MRI cross sectional area (anatomical, aCSA; physiological, pCSA). Muscle biopsy samples were analyzed for myosin heavy chain (M) and actin (A) content, and used to normalize MRI CSA (i.e. M+A CSA). In addition, a subset of 12 young (25 ± 2y) and 12 old (79 ± 7y) individuals were studied for single muscle fiber Po, CSA, and specific tension, (ST, Po/CSA). RESULTS: Whole muscle Po (−36%), aCSA (−21%), pCSA (−23%), were lower (p < 0.05) in old compared to young. Normalized Po to aCSA (−21%) and pCSA (−17%) were lower (p < 0.05) in old compared to young. M and A content (per mg muscle wet wt.) were unchanged (p > 0.05) from young to old. Po/M+A aCSA and Po/M+A pCSA were similar in young and old (p > 0.05). Single muscle fiber ST of MHC I and IIa were similar (p > 0.05) between young and old, MHC I 94 ± 22 vs. 93 ± 18 and MHC IIa 122 ± 25 vs. 133 ± 33 kN. m-2, respectively. CONCLUSION: These data suggest that aging whole muscle quality does not reflect myocellular muscle quality (i.e., single fiber ST), unless whole muscle quality accounts for the M and A content of the CSA. NIH grants R21 AG15833, K01 AG00831 (TT), and M01 RR14288.