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Institute for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Stoke-on-Trent, United Kingdom
Submitted 15 November 2005 ; accepted in final form 1 February 2006
We tested the hypothesis that compromised postural balance in older subjects is associated with changes in calf muscle-tendon physiological and mechanical properties. Trial duration and center of pressure (COP) displacements were measured in 24 younger (aged 24 ± 1 yr), 10 middle-aged (aged 46 ± 1 yr), and 36 older (aged 68 ± 1 yr) healthy subjects under varying levels of postural difficulty. Muscle-tendon characteristics were assessed by dynamometry, twitch superimposition, and ultrasonography. In tandem and single-leg stances, trial duration decreased (
65% lower, P < 0.001) and COP displacements increased (
90% higher, P < 0.05) with age. Muscle strength, size, activation capacity, and tendon mechanical properties decreased with age by 55, 13, 13, and 3648%, respectively (P < 0.05). Regressions with these parameters and balance indexes were significant (P < 0.05) for single-leg and tandem (0.69 < r2 < 0.90) postures only, indicating that the age-related changes in muscle-tendon characteristics may explain the majority of the variance in balance performance during tasks more difficult than habitual bipedal stance.
ageing; center of pressure displacement; in vivo muscle-tendon mechanical properties; postural balance; trial duration
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