Walking with an actuated ankle exoskeleton alters gait control across multiple levels during steady walking, increasing stride-to-stride variability and local dynamic stability at the lower leg and foot, while global gait stability remained unchanged.
Key Findings
Results
Walking with an actuated ankle exoskeleton increased stride-to-stride spatiotemporal variability in stride length and stance ratio.
Coefficient of variation (CoV) for stride length was significantly higher in the exoskeleton condition (p < 0.001).
CoV for stance ratio was also significantly higher with the exoskeleton (p = 0.005).
Mean stride length and step width remained unchanged between conditions.
Step width CoV was not reported as significantly different between conditions.
18 healthy adults walked at a constant treadmill speed of 1.1 m/s in a randomized crossover design.
Results
Mean stance ratio was reduced when walking with the ankle exoskeleton compared to walking without it.
The reduction in mean stance ratio was statistically significant (p < 0.001).
This indicates the exoskeleton altered the temporal distribution of the gait cycle.
Mean stride length and step width were not significantly affected by the exoskeleton condition.
Results
Global gait stability, as measured by detrended fluctuation analysis of stride time, did not differ between the exoskeleton and control conditions.
Detrended fluctuation analysis (DFA) was used to assess long-range temporal gait organization.
No significant difference in DFA scaling exponent was found between conditions.
This indicates that wearing the actuated ankle exoskeleton preserved the long-range temporal organization of gait.
Paired-samples two-sided t-tests were used for all comparisons.
Results
Local dynamic stability increased at the lower leg and foot when walking with the actuated ankle exoskeleton.
Maximum Lyapunov exponent (LyE) at the lower leg was significantly reduced (indicating greater stability) in the exoskeleton condition (p < 0.001).
Maximum Lyapunov exponent at the foot was also significantly reduced in the exoskeleton condition (p = 0.019).
Local dynamic stability was assessed at five segments: trunk, hip, upper leg, lower leg, and foot.
No significant differences in local dynamic stability were found at the trunk, hip, or upper leg.
The authors interpret this as reflecting 'segment-specific effects of ankle-level assistance close to the assisted joint.'
Methods
The study employed a randomized crossover design comparing bilateral actuated ankle exoskeleton walking to normal walking in healthy adults.
Eighteen healthy adults participated in the controlled laboratory study.
Participants walked on a treadmill at a constant speed of 1.1 m/s.
Conditions included walking with and without a bilateral actuated ankle exoskeleton.
Spatiotemporal variability was quantified using CoV of stride length, step width, and stance ratio.
Inertial measurement units or similar sensors were used to calculate maximum Lyapunov exponents for multiple body segments.
Discussion
The authors caution that findings reflect the combined effect of wearing the exoskeleton and receiving active plantarflexion assistance, not the isolated effect of assistance alone.
The study did not include a passive or unpowered exoskeleton condition, preventing isolation of mechanical loading effects from active assistance effects.
The authors state results 'should be interpreted as the combined effect of wearing the exoskeleton and receiving active assistance, rather than the isolated effect of plantarflexion assistance.'
This distinction is highlighted as a limitation relevant to interpreting the stability findings.
The authors suggest these results 'provide insight for the design and control of ankle exoskeletons with respect to stability-related effects during walking.'
What This Means
This research suggests that wearing a powered ankle exoskeleton — a robotic device strapped to the lower leg and foot that assists with push-off during walking — changes how people control their gait in several ways at the same time. In a lab study with 18 healthy adults walking on a treadmill, researchers found that people wearing the device had more step-to-step variability in how long their strides were and how long they spent with their foot on the ground, even though their average stride length didn't change. At the same time, the overall rhythmic pattern of their walking (how regular the timing was across many steps) was not disrupted by wearing the device.
Interestingly, the exoskeleton actually improved a measure called 'local dynamic stability' specifically at the lower leg and foot — the body parts closest to where the device provides assistance — while having no significant effect on stability at the upper leg, hip, or trunk. This suggests the device's effects on stability are localized near the ankle joint rather than spreading throughout the whole body. These two seemingly contradictory findings — more variability in some measures but better local stability near the foot — together paint a picture of how the body adapts its movement control when assisted by a robotic device.
This research matters because ankle exoskeletons are increasingly being developed not just to reduce the energy cost of walking, but potentially to help people with movement impairments. Understanding how these devices affect walking stability — not just efficiency — is important for making sure they are safe to use. The authors note that their findings capture the combined effect of wearing the physical device and receiving its active assistance, and future studies separating these factors would help clarify exactly what drives each effect.
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Kettner C, Beyerlein M, Marquardt C, Dežman M, Asfour T, Stein T. (2026). Effects of an actuated ankle exoskeleton on walking stability in healthy adults: a controlled laboratory study.. Journal of neuroengineering and rehabilitation. https://doi.org/10.1186/s12984-026-02151-y