Muscle Adaptation and Challenges to Motor Stability During Walking in Young Healthy Individuals

Schoenfeld, Jason
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University of Delaware
It is well established that humans adapt to sudden or unexpected perturbations through a posture control system that has vestibular, visual, proprioceptive, and sensory components. Older adults, however, are not able to generate postural responses as quickly as young adults when environmental conditions or sensory cues change rapidly. The slower postural responses may arise from progressive degeneration of the nervous system as a result of normal aging. To investigate the neuromuscular responses at the knee to perturbations during walking, ten “young healthy” (mean= 21.9 years; range= 20-23; sex= 4 males) and ten healthy “older adults” (mean= 63 years; range= 52-73; sex= 7 males) walked for 10 level trials across a 13 m walkway. Next, they walked for 30 trials across a custom-built, movable platform (NSK Ltd, Tokyo, Japan) that translated laterally when stepped upon. EMG and knee kinematic data were collected. Subjects also underwent knee proprioception and stiffness testing on a custom built Stiffness and Proprioception Assessment Device (SPAD). There were no group differences in the magnitude of muscle activation in response to the first perturbation, or in the rate of adaptation over the first five trials. However, there were differences in the strategies used by the young subjects and the older adults. The younger subjects walked more quickly and moved their knees faster during the perturbation, whereas the older subjects did not. In younger subjects, the quadriceps and hamstring muscle activation during all three phases of stance were related to the knee kinematics, whereas in older subjects, the gastrocnemius muscle activation during the preparation phase was the only muscle response related to knee kinematics. These data suggest that normal aging is associated with changes in knee control strategies. Whether those strategies are related to other conditions related to age, such as knee osteoarthritis, warrants further investigation.