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.