The Body’s Compensatory Responses to Unpredictable Trip and Slip Perturbations Induced by a Programmable Split-Belt Treadmill

Abstract

This paper investigates the influence of two types of gait perturbation (i.e., trip and slip) induced by a programmable split-belt treadmill on the body's compensatory responses. Our fall-inducing technology equipped with a commercially available programmable split-belt treadmill provides unpredictable trip and slip perturbations during walking. Two force plates beneath the split-belt treadmill and a motion capture system quantify the body's kinetic and kinematic behaviors, and a wireless surface electromyography (EMG) system evaluates the lower limb muscle activity. Twenty healthy young adults participated. The perturbations (i.e., trip and slip) were applied randomly to the participant's left foot between the 31st and 40th steps. The kinetic and kinematic behaviors and lower limb muscle activity were assessed during the standing, walking, and recovery periods. Compared with trip perturbations, stepping responses to slip perturbations were quicker and trunk, shoulder, and whole body center of mass movements after slip perturbations were higher; the EMG results showed that tibialis anterior, gastrocnemius, rectus femoris, and biceps femoris activities were also higher. The two common types of gait perturbation (i.e., trip and slip) induced by a commercially available programmable split-belt treadmill influenced the body's compensatory responses.

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“…The equipment shown in Fig 1 has been used recently [25,26]. The fall-inducing platform including a programmable split-belt treadmill equipped with two force plates located beneath each belt (Bertec, Columbus, OH, USA) and controlled by our custom software [18,19,27] was used to induce slips by accelerating the left belt in the anterior direction (i.e., the perturbation occurred at the foot level).…”

“…All trials ended 10 steps after the perturbation to account for the number of steps required to return to normal walking [19,30] and the latency of the hemodynamic response subsequent to the perturbation (approximately 4 to 7 s) [34]. Normal walking resumed within 3 to 4 steps after a slip, corresponding to 4.2 ± 0.9 s. In all trials, during standing and walking, participants were required to fix their gaze on an "X" placed approximately 4.5 m ahead at eye level to stabilize their posture and minimize head movements and side-to-side walking variations [25,26]. Consecutive trials were separated by a rest period (20 s) to allow brief relaxation of the torso and upper and lower extremities.…”

“…The body kinematics and GRF signals were low pass filtered at 10 Hz [46]. To assess kinematic and kinetic responses following slip perturbations, trunk angular dispersion (AD), trunk range of motion (ROM), COM ROM, minimum COM (Min COM) position, and response step time of the right foot (i.e., non-slip foot) were quantified [19,[25][26][27]. Trunk AD, trunk…”

Aging Affects Lower Limb Joint Moments and Muscle Responses to a Split-Belt Treadmill Perturbation

“…Based on the results of our previous studies (Lee et al, 2017a(Lee et al, ,b, 2019(Lee et al, , 2020Yoo et al, 2019) and our pilot study, the power analysis indicated a minimum of 20 participants, with an effect size (f ) = 0.67 (large effect size) (Cohen, 1992) The Nexus 1.8 software synchronized with the EMG system and the custom software sampled the EMG signals at 2000 Hz and the marker positions and the ground reaction forces (GRFs) at 100 Hz, respectively [see the detailed algorithm information in (Lee et al, 2017a); see the custom software information in (Lee et al, 2017a(Lee et al, , 2019Yoo et al, 2019)]. The custom software generated split-belt treadmill perturbations (at the foot level) by stopping the treadmill's left belt within 100 ms at a rate of 10 m/s 2 at 10% of the gait cycle (approximately the loading phase) determined by GRFs (Lee et al, 2017a(Lee et al, , 2020Yoo et al, 2019).…”

“…The Plug-in-Gait model is a standard and reliable tool in biomechanics research for analyzing joint moments, especially for the sagittal plane (Kadaba et al, 1989). Previous studies found that the whole-body movement predominated in the sagittal plane after trip perturbations (Lee et al, 2017a(Lee et al, , 2019. The low-pass filter was applied to the GRFs by a secondorder Butterworth filter with a cut-off frequency of 10 Hz using MATLAB (The MathWorks, Natick, MA, USA) (Lee et al, 2019).…”