The Next Step in Understanding Impaired Reactive Balance Control in People With Stroke: The Role of Defective Early Automatic Postural Responses.
Digna de Kam, Jolanda M B Roelofs, Amber K B D Bruijnes and 2 others
PMID 28691582WHAT IT FOUND
People with chronic stroke had impaired reactive stepping, especially sideways, and delayed and smaller paretic hip abductor responses.
Their feet-in-place balance capacity was similar to controls.
Key findings
01People with stroke had substantially impaired multiple stepping thresholds in all directions, while single stepping thresholds were not clearly different from controls.
02Paretic leg postural muscle responses were delayed by 19 ms compared with the non-paretic leg and by 18 ms compared with controls, and paretic response amplitudes were smaller by 0.01 mV compared with controls and by 0.02 mV compared with the non-paretic leg.
03Side steps were less common toward the paretic side (29% of trials) than toward the non-paretic side (61%) or controls (55%), and delayed or smaller gluteus medius responses were associated with lower sideways multiple stepping thresholds toward the paretic side.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study was cross-sectional and did not test an intervention, so it cannot show that impaired early postural responses caused the stepping deficits or that training side steps improves balance or prevents falls. People were more than 6 months after stroke and could stand and walk independently or under supervision, so the findings may not apply to acute stroke or people who cannot ambulate. Some stroke participants could not complete all high-intensity trials, especially toward the paretic side, because of fatigue or because the perturbation was too challenging. Single stepping thresholds and multiple stepping thresholds were measured on separate days, so day-to-day variation may have weakened the relationships. For forward perturbations, all controls and 16 stroke participants reached the maximum multiple stepping threshold score of 4.5 m/s2, which limited detection of relationships. Only forward, backward, leftward, and rightward perturbations were tested, not diagonal directions. The large number of trials may have caused learning and fatigue effects. EMG amplitude can be influenced by background noise, skin impedance, stroke-related muscle atrophy, loss of type 2 muscle fibers, and fewer motor units. The platform deceleration may have helped participants regain balance, but in 95% of trials the step was completed within 800 ms. The paper states this had a minor effect on group performance.
Declared interests
The authors declared no potential conflicts of interest for the research, authorship, and publication of this article. Funding was a Veni Grant given to Dr Vivian Weerdesteyn.
The easy way to misread this
Do not conclude that impaired early postural responses caused the stepping deficits or that side-step training will improve balance. This study measured associations in people with chronic stroke and did not test any intervention.