Effect of Age and Peripheral Neuropathy on Responses to an Unexpected Underfoot Perturbation during Gait.

Advancing age and diabetic peripheral neuropathy (PN) are both associated with an increased risk of fall-related injuries, especially when walking on uneven surfaces, but little is known about the effect of even a single unexpected underfoot perturbation on gait kinematics. The challenge of establishing the effects of such a perturbation arises from the difficulty of isolating the stimulus-response relationships due to carryover effects from earlier perturbations. To address this challenge a custom perturbing shoe was invented to present a single unexpected medial or lateral underfoot perturbation during level gait. The shoe was used to test the primary hypotheses that both age and increasing severity of PN would affect the kinematic response to these perturbations, chiefly by affecting myoelectric latencies, ankle proprioceptive thresholds, and ankle and hip muscle strength capacities. We recruited 42 older subjects with and without PN and 26 healthy young subjects. We measured manual reaction times, unipedal balance times, lower extremity strength capacities, gait kinematics, lower extremity electromyographic latencies and ground reaction forces during gait trials with underfoot perturbations randomly presented in 16 of 60 gait trials. The results showed that hip strength was a significant predictor of unipedal stance time (R2 = 0.73). Hip abduction/adduction and ankle inversion strengths explained almost 70% of the variation in gait speed over an uneven surface. The perturbing shoe proved a reliable method for affecting step kinematics following an unexpected underfoot perturbation. In healthy young adults, the single perturbation affected the kinematics of up to four of recovery steps but not pelvic displacements. Despite exhibiting EMG responses on the first recovery step, healthy older adults chose to alter their lateral pelvic displacements, but not recovery step kinematics. Subjects with moderate PN did not display early EMG or step kinematic responses, but larger lateral pelvic displacements than the healthy older adults. These results suggest that with advancing age and PN, subjects employ a stance limb hip response rather than an ankle response to recover from a single underfoot perturbation. These results suggest that future interventions for patients with moderate PN should aim to increase maximum hip strength and rate of strength development.PHDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/93939/1/hogenek_1.pd