Fast and slow myofiber nuclei, satellite cells, and size distribution with lifelong endurance exercise in men and women

Abstract

We previously observed lifelong endurance exercise (LLE) influenced quadriceps whole-muscle and myofiber size in a fiber-type and sex-specific manner. The current follow-up exploratory investigation examined myofiber size regulators and myofiber size distribution in vastus lateralis biopsies from these same LLE men (n = 21, 74 ± 1 years) and women (n = 7, 72 ± 2 years) as well as old, healthy nonexercisers (OH; men: n = 10, 75 ± 1 years; women: n = 10, 75 ± 1 years) and young exercisers (YE; men: n = 10, 25 ± 1 years; women: n = 10, 25 ± 1 years). LLE exercised ~5 days/week, ~7 h/week for the previous 52 ± 1 years. Slow (myosin heavy chain (MHC) I) and fast (MHC IIa) myofiber nuclei/fiber, myonuclear domain, satellite cells/fiber, and satellite cell density were not influenced (p > 0.05) by LLE in men and women. The aging groups had ~50%-60% higher proportion of large (>7000 μm²) and small (<3000 μm²) myofibers (OH; men: 44%, women: 48%, LLE; men: 42%, women: 42%, YE; men: 27%, women: 29%). LLE men had triple the proportion of large slow fibers (LLE: 21%, YE: 7%, OH: 7%), while LLE women had more small slow fibers (LLE: 15%, YE: 8%, OH: 9%). LLE reduced by ~50% the proportion of small fast (MHC II containing) fibers in the aging men (OH: 14%, LLE: 7%) and women (OH: 35%, LLE: 18%). These data, coupled with previous findings, suggest that myonuclei and satellite cell content are uninfluenced by lifelong endurance exercise in men ~60-90 years, and this now also extends to septuagenarian lifelong endurance exercise women. Additionally, lifelong endurance exercise appears to influence the relative abundance of small and large myofibers (fast and slow) differently between men and women.

Keywords: aging; cross‐sectional area; fiber type specific; masters athletes; myonuclei; satellite cells.

FIGURE 1

Fiber type specific myonuclear content, myonuclear domain, satellite cell content, and satellite cell density in men. LLE, lifelong excercisers; MHC, myosin heavy chain; OH, old healthy; YE, young exercisers; μm², micrometers squared. There was a trend (p = 0.07) for LLE to have a greater satellite cell density in MHC IIa fibers compared to YE. Data are mean ± SD, along with individual data.

FIGURE 2

Fiber type specific myonuclear content, myonuclear domain, satellite cell content, and satellite cell density in women. LLE, lifelong excercisers; MHC, myosin heavy chain; OH, old healthy; YE, young exercisers; μm², micrometers squared. There was a trend (p = 0.06) for LLE to have a greater satellite cell density in MHC IIa fibers compared to YE. Data are mean ± SD, along with individual data.

FIGURE 3

Skeletal muscle fiber type specific cross‐sectional area distribution in YE, LLE, and OH men. Gray shading highlights fibers 3000–7000 μm². Fibers <3000 μm² were considered “small” and fibers >7000 μm² were considered “large”. LLE, lifelong excercisers; MHC, myosin heavy chain; OH, old healthy; YE, young exercisers; μm², micrometers squared.

FIGURE 4

Skeletal muscle fiber type specific cross‐sectional area distribution in YE, LLE, and OH women. Gray shading highlights fibers 3000–7000 μm². Fibers <3000 μm² were considered “small” and fibers >7000 μm² were considered “large”. LLE, lifelong exercisers; MHC, myosin heavy chain; OH, old healthy; YE, young exercisers.

FIGURE 5

Skeletal muscle fiber type specific cross‐sectional area distribution in LLE‐P and LLE‐F men. Gray shading highlights fibers 3000–7000 μm². Fibers <3000 μm² were considered “small” and fibers >7000 μm² were considered “large”. LLE‐F, lifelong exercisers‐fitness; LLE‐P, lifelong exercisers‐performance; MHC, myosin heavy chain; μm², micrometers squared.