Improved single muscle fiber quality in the oldest-old

Abstract

We examined single muscle fiber contractile function of the oldest-old (3F/2M, 89 ± 1 yr old) enrolled in The Health, Aging, and Body Composition Study (The Health ABC 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 (5,576 ± 333 μm²; n = 58) was 21% larger (P < 0.05) than MHC IIa fibers (4,518 ± 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/l, respectively. Compared with previous research from our lab using identical procedures, MHC I normalized power was 28% higher than healthy 20 yr olds and similar to younger octogenarians (∼80 yr old). Normalized power of MHC IIa fibers was 63% greater than 20 yr 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.

Keywords: aging; contractile function; muscle quality; oldest-old; single fiber.

Fig. 1.

SDS-PAGE gel image of single muscle fibers from a Health ABC Study participant analyzed for MHC fiber type. Each lane represents a single muscle fiber with arrows representing MHC I and IIa isoforms.

Fig. 2.

Normalized power (W/l) distribution of MHC I (A) and MHC IIa (B) single muscle fibers from 20-, 80-, and 90-yr-old individuals. Symbols represent individual muscle fibers from 20-yr-old healthy (n = 12, 6F/6M) (67); 80-yr-old healthy (n = 6M) (61); 90-yr-old healthy (n = 3F/2M) (current study). Dotted lines at 2 and 10 W/l represent average normalized power values in a large sample of older men and women (70–82 yr old) for MHC I and IIa fibers, respectively (61). All data were collected in the Human Performance Laboratory at Ball State University using identical procedures and instrumentation.

Fig. 3.

The effect of aging on MHC I (A) and MHC IIa (B) single fiber normalized power. Fiber type-specific normalized power comparisons were made to previous research from our lab using identical procedures. Data retrieved from young cross-country runners (n = 8M) (30); young healthy inactive (n = 12, 6F/6M) (67); middle age master's runners (n = 6M) and healthy inactive (n = 5M) (73); 80 yr old healthy (n = 6M) (61); 90 yr old healthy (n = 5, 3F/2M) (current study); SCI (n = 5M, 33 yr old) (45); Champion sprint runner (68). XC, cross-country; SCI, spinal cord injured.