Background: Strength of lower extremity muscles is an important determinant of mobility-based functional activities. Loss of strength with age produces functional limitation in activities of daily living such as rising from a chair or stair negotiation. However, there is limited information on the effect of age-related changes on the torque-producing ability of muscles through their ranges of joint motion. Objective: To investigate the effect of ageing on the torque-producing ability of lower extremity muscles in a large sample of older adults in three age groups. Methods: Eighty-two volunteers participated in this study and were divided into six groups according to their chronological age (60s, 70s and 80s and above) and gender (male, female). Isometric muscle strength was measured at the knee and hip joints at three positions through the joint range using a custom-built strain gauge torque dynamometer and a purpose built plinth. Results: The peak torque of major muscle groups of the knee and hip joints decreased with increasing age at all the three joint positions at which strength was tested. The 80-year-olds had 20% lower strength compared to the 60-year-olds. Age-related decrease in muscle strength was significant when comparing 80-year-olds with the 60-year-olds (p < 0.05). Strength loss was noted to be higher at the inner (muscle is shortened from mid-position) and outer (muscle is lengthened from mid-position) ranges of muscle action when compared with the mid-range position (mid-position). Gender-based differences were significant for all the strength tests (p < 0.05). Conclusions: Strength decreased with increasing age at all the positions within joint range of motion for knee and hip joints. However, the percentage loss of muscle strength was different at different positions in the joint range. Our findings suggest that muscle strength was more preserved in the middle range of muscle function compared to the inner and outer range of muscle action. In older people, lower extremity muscles might be required to produce higher moments in joint positions that are not within the optimum mid-position for muscle action.
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