Skeletal Muscle Hypertrophy Following Resistance Training Is Accompanied by a Fiber Type–Specific Increase in Satellite Cell Content in Elderly Men

We determined muscle fiber type–specific hypertrophy and changes in satellite cell (SC) content following a 12-week resistance training program in 13 healthy, elderly men (72 ± 2 years). Leg strength and body composition (dual-energy X-ray absorptiometry and computed tomography) were assessed, and muscle biopsy samples were collected. Leg strength increased 25%–30% after training (p < .001). Leg lean mass and quadriceps cross-sectional area increased 6%–9% (p < .001). At baseline, mean fiber area and SC content were smaller in the Type II versus Type I muscle fibers (p < .01). Following training, Type II muscle fiber area increased from 5,438 ± 319 to 6,982 ± 503 μm2 (p < .01). Type II muscle fiber SC content increased from 0.048 ± 0.003 to 0.084 ± 0.008 SCs per fiber (p < .001). No changes were observed in the Type I muscle fibers. In older adults, skeletal muscle tissue is still capable of inducing SC proliferation and differentiation, resulting in Type II muscle fiber hypertrophy.