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Browsing by Author "Madinei, Saman"

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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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    Estimating lumbar spine loading when using back-support exoskeletons in lifting tasks
    Madinei, Saman; Nussbaum, Maury A. (Elsevier, 2023-01)
    Low-back pain (LBP) continues as the leading cause of work-related musculoskeletal disorders, and the high LBP burden is attributed largely to physical risk factors prevalent in manual material handling tasks. Industrial back-support exoskeletons (BSEs) are a promising ergonomic intervention to help control/prevent exposures to such risk factors. While earlier research has demonstrated beneficial effects of BSEs in terms of reductions in superficial back muscle activity, limited evidence is available regarding the impacts of these devices on spine loads. We evaluated the effects of two passive BSEs (BackX™ AC and Laevo™ V2.5) on lumbosacral compression and shear forces during repetitive lifting using an optimization-based model. Eighteen participants (gender-balanced) completed four minutes of repetitive lifting in nine different conditions, involving symmetric and asymmetric postures when using the BSEs (along with no BSE as a control condition). Using both BSEs reduced estimated peak compression and anteroposterior shear forces (by ~8-15%). Such reductions, however, were task-specific and depended on the BSE design. Laevo™ use reduced mediolateral shear forces during asymmetric lifting (by ~35%). We also found that reductions in composite measures of trunk muscle activity may not correspond well with changes in spine forces when using a BSE. These results can help guide the proper selection and application of BSEs during repetitive lifting tasks. Future work is recommended to explore the viability of different biomechanical models to assess changes in spine mechanical loads when using BSEs and whether reasonable estimates would be obtained using such models.
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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.