The relation between force production at different hip angles and functional capacity in older women

Although hip muscles are related to activities of daily living (ADLs) in older adults, there is a lack of evidence concerning the extensor-flexor hip torque-angle. A shift of the torque-angle relationship is caused by the aging process (increasing or reducing the range of motion) affecting the force production in a given muscular length during ADLs. Thus, the relationship between hip extensor-flexor muscles' force production and their association with functional capacity tests in elderly women were evaluated. Seventeen elderly women performed timed up and go, timed up and down stairs, and 30-s chair stand tests. Hip extensor-flexor isometric peak torques at 15°, 60°, 90°, and 100° (0° = full extension) were also assessed. Hip flexors produced the highest absolute and relative peak torque at a 15° angle and hip extensor muscles at 100°. A large and significant correlation (r = 0.62, p = 0.008) was observed only between absolute hip extensor peak torque at 90° and the 30-s chair stand test. When peak torque was normalized by body mass, the hip extensor-flexor muscles' peak torque obtained at all measured angles presented significant correlation with the 30-s chair stand test. The results indicate that for older women there is an optimum torque-angle for the hip flexor and extensor muscles. Furthermore, although the hip torque-angle relationship was measured under isometric contractions, there was a correlation with the 30-s chair stand test, which could indicate the presence of the isometric component during this movement.