Chronic obstructive pulmonary disease patients increase medio-lateral stability and limit changes in antero-posterior stability to curb energy expenditure.
Farahnaz Fallahtafti, Carolin Curtze, Kaeli Samson and 1 others
PMID 31683184WHAT IT FOUND
COPD patients did not show lower front-to-back step-to-step stability than controls, but had larger side-to-side margins.
They kept front-to-back margins steady as speed rose, while controls reduced them. Larger front-to-back margins coincided with lower energy cost.
Key findings
01After adjusting for step width, patients with COPD had larger side-to-side mean stability margins than healthy controls.
02Healthy controls had smaller front-to-back mean stability margins at 20% faster than self-selected speed, while patients with COPD did not significantly change between self-selected and 20% faster speeds.
03Larger front-to-back mean stability margins were associated with lower metabolic power, and greater front-to-back variability with higher metabolic power, but side-to-side stability was not associated.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study included only 17 patients with COPD and 23 healthy controls, so findings are limited by small sample size. It was a secondary analysis of a previous study, not an intervention trial. No treatment was tested, so it cannot show that changing stability or energy expenditure improves walking or falls. Patients with COPD chose a much slower self-selected speed than controls (p=0.001), which may have changed the number of strides and affected variability calculations. The authors note that treadmill speed, heel marker placement, and heel strike timing may affect front-to-back margin calculations.
Declared interests
The authors have no conflicts of interest to disclose. The study was supported by NIH extramural research funding.
The easy way to misread this
Do not conclude that COPD patients deliberately increase side-to-side stability to save energy. The study observed associations and tested no intervention, so it cannot show cause.