Capacity to increase walking speed is limited by impaired hip and ankle power generation in lower functioning persons post-stroke

Abstract

While limited walking speed characterizes gait in the majority of persons post-stroke, the potential to increase walking speed can also be markedly impaired and has not been thoroughly investigated. We hypothesized that failure to effectively recruit both hip flexor and plantarflexor muscles of the paretic side limits the potential to increase walking speed in lower functioning hemiparetic subjects. To test this hypothesis, we measured gait kinematics and mechanics of twelve persons with poststroke hemiparesis at self-selected and fast walking conditions. Two groups were identified: 1) lower functioning subjects (n=6) who increased normalized walking speed from 0.52 leg lengths/sec (ll/s, SEM: 0.04) to 0.72 ll/s (SEM: 0.03) and 2) higher functioning subjects (n = 6) who increased walking speed from 0.88 ll/s (SEM:0.04) to 1.4 ll/s (SEM 0.03). Changes in spatiotemporal parameters, joint kinematics and kinetics between self-selected and fast walking were compared to control data collected at matched speeds (0.35 ll/s (SEM: 0.03) -0.63 ll/s (SEM: 0.03) -0.92 ll/s (SEM: 0.04) and 1.4 ll/s (SEM: 0.04)). Similar to speed-matched control subjects, the higher functioning hemiparetic subjects increased paretic limb hip flexion power and ankle plantarflexion power to increase walking speed. The lower functioning subjects demonstrated impaired ankle power generation combined with excessive power generation at the paretic hip during pre-swing at their self selected speed. This lower functioning group did not increase power generation at the hip or ankle to increase walking speed. This observation suggests that impaired ankle power generation combined with saturation of hip power generation, limits the potential to increase walking speed in lower functioning hemiparetic subjects.

Linking the mechanics and energetics of hopping with elastic ankle exoskeletons

“…Elastic stretch and recoil of the Achilles tendon occurs in both walking and running (30), and thus more sophisticated elastic ankle exoskeletons that account for the more complex kinematics of these motions could assist ankle push-off and reduce the metabolic costs of these motions. This could benefit certain pathological populations who simultaneously lack ankle push-off and incur elevated metabolic costs during locomotion [e.g., poststroke or with cerebral palsy (21,27,38)]. They might also reduce musculoskeletal loading and offset increases in metabolic cost for individuals who must carry heavy additional loads, such as certain military personnel.…”

Walking velocity and lower limb coordination in hemiparesis

“…These impairments are associated with various gait abnormalities, such as gait asymmetry [5], excessive energy costs [6], altered joint kinematics and kinetics such as inadequate propulsion from the paretic limb in late stance [7,8], and compensatory activity in the non-paretic limb [5,9]. Despite these abnormalities, subjects with hemiparesis are able to increase gait velocity up to twice their preferred speed, in association with changes in segmental angular displacement (such as increased hip and knee flexion in swing phase), and increased hip and ankle kinetics [8,10,11]. In healthy subjects, increase in gait velocity occurs also through increased angular hip and ankle displacement [12,13].…”

The influence of a unilateral fixed ankle on metabolic and mechanical demands during walking in unimpaired young adults

“…For example, reduced ankle torque generation on one side of the body can be compensated for by generating more mechanical power with the contralateral limb (Allen et al, 2011;Chen et al, 2003;Cruz et al, 2009;Jonkers al., 2009). Increasing contralateral ankle power generation specifically, might limit increases in metabolic cost by making use of the ankle's compliant muscle-tendons (i.e., longer elastic tendons and shorter fascicles) which may be more efficient than knee or hip muscles (Sawicki et al, 2009).…”