THE INFLUENCE OF AGING ON MUSCLE STRENGTH AND MUSCLE-FIBER CHARACTERISTICS WITH SPECIAL REFERENCE TO ECCENTRIC STRENGTH

It is well established that aging seriously reduces isometric and conc entric muscle strength due to atrophy, deterioration of mechanical pro perties, and motor unit loss. However, there is limited information on the impact of aging on eccentric strength despite the fact that such forces play an equally important role during daily activities. The pur pose of this study was to examine the influence of aging on three expr essions of muscle strength (isometric, concentric, and eccentric) in r elation to muscle fiber characteristics, with special emphasis on ecce ntric force. Sedentary but healthy men (age range 18-80 years, a = 60) and women (20-74 years, a = 30) were tested for maximal effort isomet ric, concentric, and eccentric (1.05, 2.09, 3.14 rads . s(-1)) quadric eps strength, body Composition, and muscle fiber characteristics of th e vastus lateralis (men only). There was a significant (p<.05) similar to 30 N per decade decline in isometric and concentric forces, but on ly 9 N per decade reduction in eccentric strength. There was a signifi cant reduction in Type II muscle fiber area with aging (p<.05). Isomet ric, eccentric, and concentric force correlated r = .33, r = .32 (p<.0 5), and r = .12 (p>.05) with Type II muscle fiber area, respectively. The correlation between age and fat-free mass/force ratio ranged from r = .39 to .43 in men and r = .27 to .50 in women. The data suggest a relative preservation of eccentric strength with aging in men and wome n that seems to bk independent of muscle mass or muscle fiber type or size.