Investigating proactive balance control in individuals with incomplete spinal cord injury while walking on a known slippery surface

Abstract

BACKGROUND: Falls are a growing concern among individuals with incomplete spinal cord injury (iSCI). As many as 83% of individuals with iSCI experience at least one fall per year. Most outdoor falls occur while walking on uneven or slippery surfaces. Individuals with iSCI employ proactive balance strategies to a greater extent than able-bodied (AB) individuals during normal walking, which is effective in reducing the intensity of an unexpected slip. Whether individuals with iSCI can use proactive balance strategies in a feedforward manner to adapt to expected slip perturbations and reduce slip/fall potential while walking has not been assessed. METHODS:19 individuals with iSCI (AIS D; 14 males; 61.01 ± 17.67 years) and 17 age- and sex-matched AB individuals (13 males; 60.86 ± 17.79 years) were included in the study. Low-friction steel rollers were used to induce a slip in the anterior-posterior (AP) direction. Participants completed three walking conditions: normal walking trials (NW), one unexpected slip trial (US), and four expected slip (ES) trials. Changes in kinematic and electromyography (EMG) data were analyzed to give an indication of feedforward adaptations to the slip. Outcome variables included step width, step length, center of mass (COM) velocity, foot-floor angle, medial-lateral and AP margin of stability (MOS), maximum post-slip velocity (PSV), and integrated EMG for tibialis anterior (TA), soleus (SOL), and gluteus RESULTS: Individuals with iSCI used feedforward behavioural strategies to a greater extent than AB individuals while approaching a known slippery surface including walking with shorter steps, a flatter foot-floor angle, a more anteriorly positioned COM, and slower COM velocity. AB and iSCI groups made similar changes in their muscle activity to proactively prepare for the ES trials. The main difference between groups was a reduced ability of individuals with iSCI to proactively modulate the amplitude of the trail SOL muscle compared to AB individuals. Both AB and iSCI groups were able to make significant feedforward adjustments to behaviour and muscle activity within 1-2 trials after experiencing an US. These proactive balance strategies were effective at reducing the maximum PSV and thus the slip/fall potential in both groups. CONCLUSIONS: Results demonstrate that individuals with iSCI maintain the ability to make appropriate feedforward changes in behavior and muscle activity and do so in a similar manner to AB individuals.