Exoskeleton assistance symmetry matters: unilateral assistance reduces metabolic cost, but relatively less than bilateral assistance.

The sample was small and included only healthy male volunteers, so it does not show what happens in patients. Participants were healthy and walked symmetrically in the powered-off condition, so the study does not show what happens in patients who start with asymmetric gait. The powered-off condition included wearing both exoskeletons, so the reductions are relative to wearing an unpowered exoskeleton, not relative to walking without an exoskeleton. Two of 13 recruited participants were excluded because of exoskeleton malfunction, and 4 of 66 trials were missing. The actuation timing was optimized for bilateral assistance, so the smaller benefit in unilateral conditions could reflect suboptimal timing. The model used only three work rate levels and two asymmetry levels, so the asymmetry coefficient is a rough estimate.

Funded by Bijzonder Onderzoeksfonds and National Institutes of Health. The supplied text does not report author conflicts of interest.

Do not read this as evidence that a unilateral exoskeleton will help patients with asymmetric gait. The study tested healthy men wearing both exoskeletons, used powered-off exoskeletons as the baseline, and the authors say they do not know what would happen in patients who start off with asymmetry.