The effect of stride length on lower extremity joint kinetics at various gait speeds

Abstract

1Robot-assisted training is a promising tool under development for improving walking 2 function based on repetitive goal-oriented task practice. The challenges in developing 3 the controllers for gait training devices that promote desired changes in gait is 4 complicated by the limited understanding of the human response to robotic input. A 5 possible method of controller formulation can be based on the principle of 6 bio-inspiration, where a robot is controlled to apply the change in joint moment applied 7 by human subjects when they achieve a gait feature of interest. However, it is currently 8 unclear how lower extremity joint moments are modulated by even basic gait 9 spatio-temporal parameters. 10In this study, we investigated how sagittal plane joint moments are affected by a 11 factorial modulation of two important gait parameters: gait speed and stride length. 12November 10, 2018 1/25We present the findings obtained from 20 healthy control subjects walking at various 13 treadmill-imposed speeds and instructed to modulate stride length utilizing real-time 14 visual feedback. Implementing a continuum analysis of inverse-dynamics derived joint 15 moment profiles, we extracted the effects of gait speed and stride length on joint 16 moment throughout the gait cycle. Moreover, we utilized a torque pulse approximation 17 analysis to determine the timing and amplitude of torque pulses that approximate the 18 difference in joint moment profiles between stride length conditions, at all gait speed 19 conditions. 20Our results show that gait speed has a significant effect on the moment profiles in all 21 joints considered, while stride length has more localized effects, with the main effect 22 observed on the knee moment during stance, and smaller effects observed for the hip 23 joint moment during swing and ankle moment during the loading response. Moreover, 24our study demonstrated that trailing limb angle, a parameter of interest in programs 25 targeting propulsion at push-off, was significantly correlated with stride length. As such, 26our study has generated assistance strategies based on pulses of torque suitable for 27 implementation via a wearable exoskeleton with the objective of modulating stride 28 length, and other correlated variables such as trailing limb angle. 29 Introduction 30 Robot-assisted training is a promising tool under development for improving walking 31 function [1, 2]. A primary indicator of gait performance improvement is gait speed (GS), 32 which is associated with a better quality of life [3] and overall functional status [4]. 33 Currently, it is not well understood how the modulation of assistance provided by a 34 robot during gait training will lead to changes in GS. The gait parameter of GS is 35 known to be correlated with anterior-posterior ground reaction force, the propulsive 36 force of the foot against the ground. Furthermore, propulsive impulse, the propulsive 37 force integrated over time, is associated with the posture of the trailing limb at 38 push-off [5]. The posture of ...

Robot-aided Training of Propulsion During Walking: Effects of Torque Pulses Applied to the Hip and Knee Joints During Stance

“…In fact, the changes in both outcome measures for the single-pulse experiment were in the same direction as the changes measured in the first few strides during the repeated-pulse experiment for all conditions except one, pulse 8 -HE, whose effect size in the single-pulse experiment was close to zero (-0.057). Interestingly, the effects measured in NPI aligned with the expected modulation of TLA based on our previous biomechanical investigation [9], [10], while the effects measured in HE were usually in the opposite direction as NPI. The changes in HE and NPI measured in the repeated-pulse experiment aligned with the singlepulse experiment during pulse application, and included both positive and negative effects.…”

“…The significant three-way interaction of stride, phase, and knee torque is driven by a significant increase in NPI from stride -1 to 0 for early stance knee extension torque (change in NPI: Early Stance, Knee Ext: 3.4±0.3 ms, p < 0.001), by a significant decrease in NPI for late stance knee extension torque (change in NPI: Late Stance, Knee Ext: -2.9±0.3 ms, p < 0.001) and by a significant increase in NPI for late stance knee flexion torque (change in NPI: Late Stance, Knee Flex: 4.2±0.3 ms, p < 0.001). The significant three-way interaction of stride, phase, and hip torque is driven by a significant increase in NPI from stride -1 to 0 for early stance [10], effect size, and p value for the pulse of application relative to baseline for measured HE and NPI, (threshold p = 0.05/16 = 0.003) for each of the 16 pulse conditions in singlepulse application hip extension torque (change in NPI: Early Stance, Hip Ext: 2.8±0.3 ms, p < 0.001).…”

“…As such, we sought to develop a controller capable of training propulsion during walking. We began by investigating the changes in joint moments associated with the experimentally imposed factorial modulation of GS and TLA [9], [10]. We then approximated the effects of push-off posture on joint moments with brief pulses of joint torque.…”

“…First, we wished to investigate the instantaneous effects of single-pulse torque intervention on the kinematics and kinetics of gait. As such, for the first protocol of this study, we formulated a set of sixteen conditions of torque pulses, based on the torque patterns associated with TLA modulation in our previous study [9], [10]. The protocol consisted of applying torque pulses to the hip and knee joints of healthy individuals during single strides, using a lower extremity exoskeleton, the ALEX II, while they walked on an instrumented treadmill.…”

Training propulsion: Locomotor adaptation to accelerations of the trailing limb

“…A robotic exoskeleton that increases ankle plantarflexion torque during push off has been FS (corresponding author -fabs@udel.edu), AJF , RM, and ML are with the Human Robotics Laboratory, Department of Biomedical Engineering, University of Delaware, Newark DE, 19713 USA. shown to be metabolically advantageous during treadmill and overground walking, and is currently used during robotassisted gait training for post-stroke individuals [3], [4]. Our group is currently working on developing robotic multijoint assistance algorithms that modulate the posture of the trailing limb at push-off to increase propulsion [5], [6]. Unfortunately, wearable exoskeletons are not always feasible for gait training of stroke survivors, due to the cost of such active devices, the burden required to wear external structures, and the technical complexity of operating such devices.…”