The trade-off between hip flexors and ankle plantar flexors due to age and speed
Date
2014
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Publisher
University of Delaware
Abstract
Walking is a common activity of daily living and is directly related to an individual's quality of life. During the push-off phase of gait, the ankle plantar flexors and the hip flexors are known to propel the body into swing. The plantar flexor muscles are particularly important as they are major contributors to the energy for propulsion of the body, determining gait speed. Muscle torque shows a decline with age, evident in both men and women. A decrease in ankle plantar flexor torque would explain the decrease in gait speed common in older adults. However, in previous studies a trade-off was found between hip flexor muscles and ankle plantar flexor muscles, suggesting that the hip muscles compensate to make up for the decreased torque production in plantar flexor muscles during aging. The purpose of this study was to determine whether a relationship exists between the hip flexor and ankle plantar flexor moments for (1) older and younger subjects and (2) self-selected and fast walking speeds, as well as the underlying mechanisms responsible for the relationship. Motion capture data was analyzed for 12 subjects, 6 young (20 + 2 years) and 6 older (62 + 8 years). The subjects were equipped with reflective markers, and walked on an instrumented treadmill for two walking conditions at self-selected and fast speeds. A 6 degree-of-freedom model was created in Visual3D, reporting the kinematics during the gait cycle. Simulations were created in OpenSim to determine joint moments, individual muscle moment, muscle forces, and muscle moment arms in the ankle plantar flexors and the hip flexors from mid-stance to toe off. Healthy adults exhibit an adaptation in which they use their hip muscles more when they walk fast due to an increase in muscle force production. Older adults show the same adaptation compared with younger adults but the underlying mechanism is due to a change in kinematics. These adaptations are important to note in healthy adults to set a healthy baseline when analyzing and designing rehabilitation strategies for adults with pathologies.