Browsing by Author "Park, Jang-Ho"

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    Changes in lower-limb joint torques when using a passive back-support exoskeleton for level walking
    Park, Jang-Ho; Kim, Sunwook; Nussbaum, Maury A.; Srinivasan, Divya (SAGE, 2021-09)
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    Effects of back-support exoskeleton use on gait performance and stability during level walking
    Park, Jang-Ho; Kim, Sunwook; Nussbaum, Maury A.; Srinivasan, Divya (Elsevier, 2022-02-01)
    Background: Back-support exoskeletons (BSEs) are a promising intervention to mitigate physical demands at work. Although growing evidence indicates that BSEs can reduce low-back physical demands, there is limited understanding of potential unintended consequences of BSE use, including the risk of falls. Research question: Does using a BSE adversely affect gait performance and stability, and are such effects dependent on specific BSE external torque characteristics? Methods: Twenty participants (10 M, 10 F) completed five level over-ground walking trials and a five-minute treadmill walking trial while wearing a BSE (backX™) with three different levels of external torque (i.e., no torque, low torque, and high torque) and in a control (no-exoskeleton) condition. Spatiotemporal gait patterns, stride-to-stride gait variability measures, required coefficient-of-friction (RCoF), and minimum foot clearance (MFC) were determined, to assess gait performance. Gait stability was quantified using the maximum Lyapunov exponent (MLE) of trunk kinematics and the margin-of-stability (MoS). Results: Using the backX™ with high supportive torque decreased slip risk (7% decrease in RCoF) and slightly improved trunk stability (3% decrease in MLE). However, it also decreased step length (1%), increased step width (10%) and increased gait variability (8–19%). Changes in MoS were complex: while MoS at heel strike decreased in the AP direction, it increased in the ML direction. There was a rather large decrease in MoS (26%) in the ML direction during the swing phase. Significance: This is the first study to quantify the effects of wearing a passive BSE with multiple supportive torque levels on gait performance and stability during level walking. Our results, showing that the external torque of the BSE may adversely affect gait step width, variability, and dynamic stability, can contribute to better design and practice guidelines to facilitate the safe adoption of BSEs in the workplace.
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    Effects of back-support exoskeleton use on lower limb joint kinematics and kinetics during level walking
    Park, Jang-Ho; Lee, Youngjae; Madinei, Saman; Kim, Sun Wook; Nussbaum, Maury A.; Srinivasan, Divya (Springer, 2022-04-27)
    We assessed the effects of using a passive back-support exoskeleton (BSE) on lower limb joint kinematics and kinetics during level walking. Twenty young, healthy participants completed level walking trials while wearing a BSE (backXTM) with three different levels of hip-extension support torque (i.e., no torque, low, and high) and in a control condition (no-BSE). When hip extension torques were required for gait-initial 0-10% and final 75-100% of the gait cycle-the BSE with high supportive torque provided ~ 10 Nm of external hip extension torque at each hip, resulting in beneficial changes in participants' gait patterns. Specifically, there was a ~ 10% reduction in muscle-generated hip extension torque and ~ 15-20% reduction in extensor power. During the stance-swing transition, however, BSE use produced undesirable changes in lower limb kinematics (e.g., 5-20% increase in ankle joint velocity) and kinetics (e.g., ~ 10% increase in hip flexor, knee extensor, and ankle plantarflexor powers). These latter changes likely stemmed from the need to increase mechanical energy for propelling the leg into the swing phase. BSE use may thus increase the metabolic cost of walking. Whether such use also leads to muscle fatigue and/or postural instability in long-distance walking needs to be confirmed in future work.
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    A novel approach to quantify the assistive torque profiles generated by passive back-support exoskeletons
    Madinei, Saman; Kim, Sunwook; Park, Jang-Ho; Srinivasan, Divya; Nussbaum, Maury A. (Elsevier, 2022-10-31)
    Industrial exoskeletons are a promising ergonomic intervention to reduce the risk of work-related musculoskeletal disorders by providing external physical support to workers. Passive exoskeletons, having no power supplies, are of particular interest given their predominance in the commercial market. Understanding the mechanical behavior of the torque generation mechanisms embedded in passive exoskeletons is, however, essential to determine the efficacy of these devices in reducing physical loads (e.g., in manual material handling tasks). We introduce a novel approach using a computerized dynamometer to quantify the assistive torque profiles of two passive back-support exoskeletons (BSEs) at different support settings and in both static and dynamic conditions. The feasibility of this approach was examined using both human subjects and a mannequin. Clear differences in assistive torque magnitudes were evident between the two BSEs, and both devices generated more assistive torques during trunk/hip flexion than extension. Assistive torques obtained from human subjects were often within similar ranges as those from the mannequin, though values were more comparable over a narrow range of flexion/extension angles due to practical limitations with the dynamometer and human subjects. Characterizing exoskeleton assistive torque profiles can help in better understanding how to select a torque profile for given task requirements and user anthropometry, and aid in predicting the potential impacts of exoskeleton use by incorporating measured torque profiles in a musculoskeletal modeling system. Future work is recommended to assess this approach for other occupational exoskeletons.
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    Wearing a back-support exoskeleton alters lower-limb joint kinetics during single-step recovery following a forward loss of balance
    Park, Jang-Ho; Madigan, Michael L.; Kim, Sunwook; Nussbaum, Maury A.; Srinivasan, Divya (Elsevier, 2024-03-31)
    We assessed the effects of a passive, back-support exoskeleton (BSE) on lower-limb joint kinetics during the initiation and swing phases of recovery from a forward loss of balance. Sixteen (8M, 8F) young, healthy participants were released from static forward-leaning postures and attempted to recover their balance with a single-step while wearing a BSE (backXTM) with different levels of support torque and in a control condition. The BSE provided ∼ 15-20 Nm of external hip extension torque on the stepping leg at the end of initiation and beginning of swing phases. Participants were unable to generate sufficient hip flexion torque, power, and work to counteract this external torque, although they sustained hip flexion torque for a more prolonged period, resulting in slightly increased hip contribution to positive leg work (compared to control). However, net positive leg work, and the net contribution of hip joint (human + BSE) to total leg work decreased with BSE use. While all participants had changes in hip joint kinetics, a significant compensatory increase in ankle contribution to positive leg work was observed only among females. Our results suggest that BSE use adversely affects reactive stepping by decreasing the stepping leg kinetic energy for forward propulsion, and that the relative contributions of lower-limb joints to total mechanical work done during balance recovery are altered by BSE use. BSEs may thus need to be implemented with caution for dynamic tasks in occupational settings, as they may impair balance recovery following a forward loss of balance.
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    Wearing a back-support exoskeleton impairs single-step balance recovery performance following a forward loss of balance – An exploratory study
    Park, Jang-Ho; Lee, Youngjae; Madigan, Michael L.; Kim, Sunwook; Nussbaum, Maury A.; Srinivasan, Divya (Elsevier, 2022-11-01)
    Back-support exoskeletons (BSEs) are a promising ergonomic intervention for reducing physical demands on the low-back, but little is known regarding whether BSE use alters balance recovery following external perturbations. Hence, we investigated the effects of wearing a BSE on single-step balance recovery following a forward loss of balance. Sixteen (8 M, 8F) young, healthy participants were released from static forward-leaning postures and attempted to recover their balance with a single step while wearing a BSE (backXTM) with three different levels of support torque (i.e., no torque, low, and high) and in a control condition (no exoskeleton). Lean angle was increased until they failed in two consecutive trials to recover their balance with a single step. The maximum lean angle from which individuals could successfully recover was not significantly altered when wearing the BSE. However, wearing the BSE under all torque conditions increased reaction times. The BSE also impeded hip flexion (i.e., decrease in both peak hip flexion angle and angular velocity), resulting in decreased peak knee flexion velocity, knee range of motion, and step length. Measures of the margin of stability decreased significantly in the high-torque BSE condition. Overall, our results suggest that use of a BSE that provides external hip extension torque impairs balance recovery responses. Future work extending kinetic analyses to recovery responses, as well as a study of recovery when responding to slips and trips while walking, would offer a more complete picture of how a BSE may impact balance recovery following a loss of balance.