Introduction: Both sarcopenia and spinal cord injury (SCI) are characterized by the loss of skeletal muscle mass and function. Despite obvious similarities in atrophy between both models, differences in muscle fiber size and satellite cell content may exist on a muscle fiber type–specific level.
Methods: In the present study, we compared skeletal muscle fiber characteristics between wheelchair-dependent young males with SCI (n = 8, 32 ± 4 yr), healthy elderly males (n = 8, 75 ± 2 yr), and young controls (n = 8, 31 ± 3 yr). Muscle biopsies were collected to determine skeletal muscle fiber type composition, fiber size, and satellite cell content.
Results: Severe atrophy and a shift toward approximately 90% Type II muscle fibers were observed in muscle obtained from males with SCI. Muscle fiber size was substantially smaller in both the SCI (Types I and II fibers) and elderly subjects (Type II fibers) when compared with the controls. Satellite cell content was substantially lower in the wheelchair-dependent SCI subjects in both the Types I and II muscle fibers (0.049 ± 0.019 and 0.050 ± 0.005 satellite cells per fiber, respectively) when compared with the young controls (0.104 ± 0.011 and 0.117 ± 0.009 satellite cells per fiber, respectively). In the elderly, the number of satellite cells was lower in the Type II muscle fibers only (0.042 ± 0.005 vs 0.117 ± 0.009 satellite cells per fiber in the elderly vs young controls, respectively).
Conclusion: This is the first study to show that muscle fiber atrophy as observed with SCI (Types I and II fibers) and aging (Type II fibers) is accompanied by a muscle fiber type–specific reduction in satellite cell content in humans.
1NUTRIM School for Nutrition, Toxicology and Metabolism, Department of Human Movement Sciences, Maastricht University Medical Centre+, Maastricht, THE NETHERLANDS; 2Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, THE NETHERLANDS; 3Department of Physiology, Radboud University Nijmegen Medical Centre, Nijmegen, THE NETHERLANDS; and 4Research Institute for Sports and Exercise Sciences, Liverpool John Moores University, Liverpool, UNITED KINGDOM
Address for correspondence: Lex B. Verdijk, Ph.D., NUTRIM School for Nutrition, Toxicology and Metabolism, Department of Human Movement Sciences, Maastricht University Medical Centre+, P.O. Box 616, 6200 MD Maastricht, The Netherlands; E-mail: email@example.com.
Submitted for publication April 2012.
Accepted for publication June 2012.