Minimum Slip Perturbation Amplitudes Required to Identify Altered Kinematics and Muscle Excitations.

Monitoring instability is critical for diagnosing falls risk and preventing fall events. This study aimed to establish minimum slip perturbation amplitudes required for identification of altered signals via surface electromyography and inertial measurement units in the context of conscious perception thresholds. We tested the null hypothesis that minimum detectable amplitudes for conscious perception would be indistinguishable from those for electromyography and inertial measurement unit signals. Fifteen healthy younger adults participated. After each perturbation, participants were asked if they had perceived the perturbation. The average conscious perception threshold was 0.061 m/s (ie, Δ velocity). Minimal detectable effects were based on the fraction of signals exceeding 3 standard deviations of unperturbed walking. For electromyography, we found thresholds of 0.053 m/s for the tibialis anterior and 0.018 m/s for the gastrocnemius. For IMUs, we found thresholds for most anatomical placements of ≤0.016 m/s. Clear differences in minimal detectable amplitudes for local muscle reflexes versus conscious perception support exploring this experimental paradigm for screening in individuals with sensory, motor, and cognitive-motor pathologies. We also conclude that inertial measurement unit signals are highly sensitive to slip perturbations in walking, supporting continued development into their application for monitoring and measuring instability in the real world.