Study design Cross sectional.Objectives To compare the reactive stepping ability of individuals living with incomplete spinal cord injury or disease (SCI/ D) to that of sex-and age-matched able-bodied adults. Setting A tertiary SCI/D rehabilitation center in Canada. Methods Thirty-three individuals (20 with incomplete SCI/D) participated. Participants assumed a forward lean position in standing whilst 8-12% of their body weight was supported by a horizontal cable at waist height affixed to a rigid structure. The cable was released unexpectedly, simulating a forward fall and eliciting one or more reactive steps. Behavioral responses (i.e., single step versus non-single step) were compared using a Chi-square test. The following temporal parameters of reactive stepping were compared using t-tests: the onset of muscle activation in 12 lower extremity muscles (six per limb) and step-off, step contact and swing time of the stepping leg. Results Behavioral responses were significantly different between groups (χ 2 = 13.9 and p < 0.01) with participants with incomplete SCI/D showing more non-single step responses (i.e., multi-steps and falls). The onsets of muscle activation were more variable in participants with incomplete SCI/D, but only the stepping tibialis anterior showed a significantly slower onset in this group compared with able-bodied adults (t = −2.11 and p = 0.049). Movement timing of the stepping leg (i.e., step-off, step contact, and swing time) was not significantly different between groups. Conclusions Reactive stepping ability of individuals with incomplete SCI/D is impaired; however, this impairment is not explained by temporal parameters. The findings suggest that reactive stepping should be targeted in the rehabilitation of ambulatory individuals with SCI/D.
Individuals with motor incomplete spinal cord injuries (iSCI) often have impaired abilities to maintain upright balance. For able-bodied (AB) individuals, the ankle and hip joint accelerations are in anti-phase to minimize the postural sway during quiet standing. Here we investigated how inter-joint coordination between the ankle and hip joints was affected in individuals with iSCI leading to their larger postural sway during quiet standing. Data from sixteen individuals with iSCI, fourteen age- and sex-matched AB individuals and thirteen young AB individuals were analyzed. The participants performed quiet standing during which kinematic and kinetic data were recorded. Postural sway was quantified using center-of-pressure velocity and center-of-mass acceleration. Individual ankle and hip joint kinematics were quantified, and the inter-joint coordination was assessed using the cancellation index (CI), goal-equivalent variance (GEV), non-goal-equivalent variance (NGEV) and uncontrolled manifold (UCM) ratio. Individuals with iSCI displayed greater postural sway compared to AB individuals. The contribution of ankle angular acceleration towards one's sway was significantly greater for those with iSCI compared to AB groups. CI and the UCM ratio were not statistically different between the groups, while GEV and NGEV were significantly greater for the iSCI group compared to the AB groups. We demonstrated that individuals with iSCI show larger postural sway compared to the AB individuals during quiet standing, primarily due to larger ankle joint acceleration. We also demonstrated that the inter-joint coordination between ankle and hip joint is not affected in individuals with iSCI, which is not successfully able to reduce the large COM acceleration.
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