Aerobic exercise training improves whole muscle and single myofiber size and function in older women

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 2009-11, Vol.297 (5), p.R1452-R1459
• Main Authors: Harber, Matthew P, Konopka, Adam R, Douglass, Matthew D, Minchev, Kiril, Kaminsky, Leonard A, Trappe, Todd A, Trappe, Scott
• Format: Article
• Language: English
• Subjects: Aged; Aging - pathology; Aging - physiology; Biopsy; Exercise; Exercise - physiology; Exercise Test; Female; Humans; Knee; Magnetic Resonance Imaging; Muscle Contraction - physiology; Muscle Fibers, Fast-Twitch - pathology; Muscle Fibers, Fast-Twitch - physiology; Muscle Fibers, Slow-Twitch - pathology; Muscle Fibers, Slow-Twitch - physiology; Muscle Proteins - metabolism; Muscle, Skeletal - pathology; Muscle, Skeletal - physiology; Muscular system; NMR; Nuclear magnetic resonance; Older people; Proteins; Women
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00354.2009

Human Performance Laboratory, Ball State University, Muncie Indiana Submitted January 19, 2009 ; accepted in final form August 17, 2009 To comprehensively assess the influence of aerobic training on muscle size and function, we examined seven older women (71 ± 2 yr) before and after 12 wk of cycle ergometer training. The training program increased ( P < 0.05) aerobic capacity by 30 ± 6%. Quadriceps muscle volume, determined by magnetic resonance imaging (MRI), was 12 ± 2% greater ( P < 0.05) after training and knee extensor power increased 55 ± 7% ( P < 0.05). Muscle biopsies were obtained from the vastus lateralis to determine size and contractile properties of individual slow (MHC I) and fast (MHC IIa) myofibers, myosin light chain (MLC) composition, and muscle protein concentration. Aerobic training increased ( P < 0.05) MHC I fiber size 16 ± 5%, while MHC IIa fiber size was unchanged. MHC I peak power was elevated 21 ± 8% ( P < 0.05) after training, while MHC IIa peak power was unaltered. Peak force (Po) was unchanged in both fiber types, while normalized force (Po/cross-sectional area) was 10% lower ( P < 0.05) for both MHC I and MHC IIa fibers after training. The decrease in normalized force was likely related to a reduction ( P < 0.05) in myofibrillar protein concentration after training. In the absence of an increase in Po, the increase in MHC I peak power was mediated through an increased ( P < 0.05) maximum contraction velocity (Vo) of MHC I fibers only. The relative proportion of MLC 1s (Pre: 0.62 ± 0.01; Post: 0.58 ± 0.01) was lower ( P < 0.05) in MHC I myofibers after training, while no differences were present for MLC 2s and MLC 3f isoforms. These data indicate that aerobic exercise training improves muscle function through remodeling the contractile properties at the myofiber level, in addition to pronounced muscle hypertrophy. Progressive aerobic exercise training should be considered a viable exercise modality to combat sarcopenia in the elderly population. physical activity; elderly; hypertrophy; myosin light chain; contraction velocity Address for reprint requests and other correspondence: Matthew Harber, Human Performance Laboratory, Ball State Univ., Muncie, IN 47306 (e-mail: mharber{at}bsu.edu ).