Earliest Gait Deviations During Slips: Implications For Recovery

OCCUPATIONAL APPLICATIONS This study identified that deviations in vertical force and knee angle/angular velocity of the slipping leg occur earlier in stance and with greater magnitude than other lower-body motions when a person experiences an unexpected slip. Deviations in the ankle angle/angular velocity and hip angular velocity occurred soon after the knee angle and with smaller magnitudes. These results suggest that foot somatosensation and ankle/knee proprioception may play a role in sensing a slip. Therefore, workers with sensation loss in their foot, ankle, and/or knee may have an impaired ability to respond to slipping. Exposure to simulated slip perturbations may also be part of slip-and-fall prevention programs. To ensure biofidelity of such training perturbations, foot forces should initially be reduced, followed by extension deviations of the knee, and then plantarflexion deviations of the ankle. TECHNICAL ABSTRACT Rationale: Slip-and-fall accidents are a serious occupational and public health concern. The biomechanical deviations due to a slip occurring prior to the postural response onset are still not well understood. Understanding this period of the slip would provide insight into the sensory cues for slipping and may provide guidance in developing slip-training protocols. Purpose: This study examined the timing and magnitude of deviations in vertical force and lower-body joint angles and angular velocities of slips compared to unperturbed walking. Methods: Twenty-nine younger and 29 middle-aged participants walked under normal unperturbed conditions and during an unexpected slip. Joint angle and angular velocity trajectories and ground reaction forces were evaluated. Deviations occurring during the slipping trial that exceeded ±2.58 standard deviations (99% confidence interval) were identified as the onset of deviation from normal walking. Results: Deviation timing (and peak magnitude in the first 200 ms) of vertical force, knee angle, knee angular velocity, ankle angle, ankle angular velocity, and hip angular velocity of the slipping leg occurred at 58 ms (0.17 BW reduction), 116 ms (6.7° extension), 111 ms (87°/s extension), 156 ms (4.4° plantarflexion), 122 ms (86°/s plantarflexion), and 149 ms (18.9°/s flexion), respectively. Deviations normalized to baseline stride-to-stride standard deviation revealed largest deviations in vertical force and knee angle and then knee angular velocity and ankle angle and angular velocity. No age effects were found. Conclusions: These results suggest that foot somatosensation as well as ankle and knee proprioception from the slipping leg may be among the first sensory cues to slipping. Exposure to simulated slip perturbations may be part of slip-and-fall prevention programs. To ensure biofidelity of such perturbations, foot forces should initially be reduced, followed by extension deviations of the knee, and then plantarflexion deviations of the ankle.