Abstract
Background. Lower muscle
mass has been correlated with poor physical function; however, no studies have
examined this relationship prospectively. This study aims to investigate
whether low muscle mass, low muscle strength, and greater fat infiltration into
the muscle predict incident mobility limitation. Methods. Our study cohort
included 3075 well-functioning black and white men and women aged 70–79 years participating
in the Health, Aging, and Body Composition study. Participants were followed
for 2.5 years. Muscle crosssectional area and muscle tissue attenuation (a
measure of fat infiltration) were measured by computed tomography at the mid-thigh,
and knee extensor strength by using a KinCom dynamometer. Incident mobility
limitation was defined as two consecutive self-reports of any difficulty
walking one-quarter mile or climbing 10 steps. Results. Mobility limitations
were developed by 22.3% of the men and by 31.8% of the women. Cox’s
proportional hazards models, adjusting for demographic, lifestyle, and health
factors, showed a hazard ratio of 1.90 [95% confidence interval (CI), 1.27–2.84]
in men and 1.68 (95% CI, 1.23–2.31) in women for the lowest compared to the
highest quartile of muscle area ( p < .01 for trend). Results for muscle
strength were 2.02 (95% CI, 1.39–2.94) and 1.91 (95% CI, 1.41–2.58), p < .001
trend, and for muscle attenuation were 1.91 (95% CI, 1.31–2.83) and 1.68 (95%
CI, 1.20–2.35), p < .01 for trend. When included in one model, only muscle
attenuation and muscle strength independently predicted mobility limitation ( p
< .05). Among men and women, associations were similar for blacks and
whites. Conclusion. Lower muscle mass (smaller cross-sectional thigh muscle
area), greater fat infiltration into the muscle, and lower knee extensor muscle
strength are associated with increased risk of mobility loss in older men and
women. The association between low muscle mass and functional decline seems to
be a function of underlying muscle strength.
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