We examined single muscle fiber contractile function of the oldest-old (3F/2M, 89 ± 1 y) enrolled in The Health, Aging, and Body Composition Study. Vastus lateralis muscle biopsies were obtained and single muscle fiber function was determined (n = 105) prior to myosin heavy chain (MHC) isoform identification with sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Cross-sectional area of MHC I muscle fibers (5576 ± 333 μm2; n = 58) was 21% larger (P < 0.05) than MHC IIa fibers (4518 ± 386 μm2; n = 47). Normalized power (an indicator of muscle fiber quality incorporating size, strength, and speed) of MHC I and IIa muscle fibers was 2.3 ± 0.1 and 17.4 ± 0.8 W∙-1 respectively. Compared to previous research from our lab using identical procedures, MHC I normalized power was 28% higher than healthy 20 y olds and similar to younger octogenarians (~80 y). Normalized power of MHC IIa fibers was 63% greater than 20 y olds and 39% greater than younger octogenarians. These comparative data suggest that power output per unit size (i.e. muscle quality) of remaining muscle fibers improves with age, a phenomenon more pronounced in MHC IIa fibers. Age-related single muscle fiber quality improvements may be a compensatory mechanism to help offset decrements in whole muscle function.
- single fiber
- muscle quality
- contractile function
- Copyright © 2016, Journal of Applied Physiology