Perturbation-based estimation of within-stride cycle metabolic cost.
Alex C Dzewaltowski, Prokopios Antonellis, Arash Mohammadzadeh Gonabadi and 2 others
PMID 39090735WHAT IT FOUND
A new method estimates where energy is spent during each part of a walking step.
In healthy adults, single stance used 49% of the step's energy, swing 21%, push-off 10%, and double stance 20%. This helps target interventions like exoskeletons.
Key findings
01The perturbation-based method estimated within-stride metabolic cost with a mean correlation of 0.80 against model-based estimates in human experimental data.
02Applying the method to human breathing data showed single stance accounted for 49% of the step's metabolic cost, while push-off accounted for only 10%.
03The estimated cost of push-off was lower than single stance, despite push-off involving about three times as much positive mechanical work on the center of mass.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTs
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What it does not show
The method relies on lower-limb signals only and does not account for metabolic contributions from trunk and arm muscles. The estimation is empirical and does not explain causal relationships, such as why a specific gait impairment increases cost. Data collection requires walking under many different perturbations, which is time-consuming and physically demanding for participants. The method was validated against model-based estimates, which themselves show inconsistent correlations with each other in the literature (mean r = 0.29).
Declared interests
The study was funded by the National Science Foundation, the National Institutes of Health, and a NU Collaboration Grant. The authors declared no competing interests.
The easy way to misread this
Do not interpret the high correlation with model-based estimates as proof that the method measures true metabolic cost. The validation was against other models, not direct measurements of phase-specific energy, which is currently impossible to measure directly.