Single Muscle Fiber Characteristics of The Oldest-Old

Abstract

PURPOSE: To examine single muscle fiber function in the oldest-old. METHODS: Vastus lateralis muscle biopsies were obtained from five healthy independently living individuals (3F/2M, 89 ± 1 y) enrolled in the Health, Aging and Body Composition (Health ABC) Study. Isolated myosin heavy chain (MHC) I and IIa muscle fibers were examined for cross-sectional area (CSA) and contractile properties prior to MHC isoform identification via SDS-PAGE. RESULTS: MHC I muscle fibers were 21% larger (P < 0.05) than MHC IIa. A summary of muscle fiber characteristics is provided below (values are means ± SE). CONCLUSION: This investigation was the first to examine single muscle fiber contractile properties of independently living individuals > 85 y. In line with previous aging research, MHC IIa fibers were smaller than MHC I, indicative of MHC IIa-specific atrophy. Normalized power (an indicator of muscle fiber quality incorporating size, strength and speed) of MHC I fibers from these individuals, when compared to previous research from our lab using identical procedures, was 28% higher than healthy 25 y olds and similar to younger octogenarians (∼82 y). MHC IIa normalized power was 63% greater than 25 y olds and 39% greater than younger octogenarians. These data support the idea that power output per unit size (i.e. muscle quality) of surviving muscle fibers improves with advancing age, a phenomenon more pronounced in MHC IIa fibers. Thus, a likely key contributor to the loss of muscle function with age is a quantitative loss of whole muscle specific force rather than a reduction in muscle quality of remaining muscle fibers.Table: No title available.