Skeletal muscle hypertrophy following resistance training is accompanied by a fiber type-specific increase in satellite cell content in elderly men

Abstract

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 microm(2) (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.

Figure 1.

Muscle fiber type–specific analysis for satellite cell (SC) content. (A) myosin heavy chain-I + laminin + 4,6-diamidino-2-phenylindole (DAPI) staining from serial cross-section of images (B–D); the marked area represents the same area as shown in frames (B–D); (B) CD56 + laminin + DAPI staining; (C) CD56 staining; (D) CD56 + DAPI staining. Arrows indicate the SCs. Numbers indicate muscle fiber Type I and II.

Figure 2.

Mean number of satellite cells (SC) in the Type I and Type II muscle fibers before and after the exercise intervention program. ^#Significantly different compared with the Type I muscle fibers (p < .01); *significantly different compared with before the intervention (p < .01).