484 Journal of Aging and Physical Activity, 2008, 16, 484-493 © 2008 Human Kinetics, Inc. Association Between Muscle Mass and Isometric Muscle Strength in Well- Functioning Older Men and Women Serge Beliaeff, Danielle R. Bouchard, Christophe Hautier, Martin Brochu, and Isabelle J. Dionne This cross-sectional study examined the relationship between arm and leg muscle mass and isometric muscle strength in 465 well-functioning women and 439 well- functioning men from the NuAge cohort, age 67–84 years. Leg and arm muscle mass and body fat were measured by dual-X-ray absorptiometry. Maximum voluntary iso- metric strength of knee extensors and elbow lexors was measured using the belt- resisted method and a handheld dynamometer, respectively. The regression model including leg muscle mass, physical activity level, age, height, and body fat explained 14% of the variance in quadriceps strength in men and 11% in women (p < .001), whereas the model including arm muscle mass and the same covariates elucidated 40% and 28%, respectively, of the variance in biceps strength (p < .001). These results suggest that muscle mass does not play a crucial role in the variations of isometric muscle strength in well-functioning elderly. Keywords: elderly, physical capacity, aging Decreased muscle strength is commonly observed with age, especially after the age of 50 years (Jubrias, Odderson, Esselman, & Conley, 1997; Metter et al., 1999), and plays a signiicant role in the decline in physical function in the elderly (Landers, Hunter, Wetzstein, Bamman, & Weinsier, 2001; Rantanen et al., 1999). It is well accepted that the age-associated loss of muscle mass called sarcopenia is an underlying factor to the age-related decline in strength in older adults (Doherty, 2003; Morley, Baumgartner, Roubenoff, Mayer, & Nair, 2001; Roubenoff, 2003), although likely not a major contributor. Indeed, studies in older adults showed that muscle mass might explain 4–61% of the variance observed in muscle strength, with most of the data explaining less than 50% of the variance (Hughes et al., 2001; Landers et al.; Overend, Cunningham, Kramer, Lefcoe, & Paterson, 1992; Pearson, Bassey, & Bendall, 1985; Reed, Pearlmutter, Yochum, Meredith, & Mooradian, 1991; Young, Stokes, & Crowe, 1984; Young, Stokes, & Crowe, 1985). In these studies, both direct and indirect measures such as anthropometry The authors are with the University Institute of Geriatrics of Sherbrooke, University of Sherbrooke, Québec J1H 4C4, Canada.