Design, Modeling, and Demonstration of a New Dual-Mode Back-Assist Exosuit with Extension Mechanism.

Occupational exoskeletons and exosuits have been shown to reduce muscle demands and fatigue for physical tasks relevant to a variety of industries (e.g. logistics, construction, manufacturing, military, healthcare). However, adoption of these devices into the workforce has been slowed by practical factors related to comfort, form-factor, weight, and not interfering with movement or posture. We previously introduced an un-motorized, low-profile, dual-mode exosuit comprised of textile and elastic materials to address these adoption barriers. Here we build upon this prior work by introducing an extension mechanism that increases the moment arm of the exosuit while in engaged mode, then collapses in disengaged mode to retain key benefits related to being lightweight, low-profile, and unobstructive. Here we demonstrate both analytically and empirically how this extensible exosuit concept can (i) reduce device-to-body forces (which can improve comfort for some users and situations), or (ii) increase the magnitude of torque assistance about the low back (which may be valuable for heavy-lifting jobs) without increasing shoulder or leg forces relative to the prior form-fitting exosuit. We also introduce a novel mode-switching mechanism, as well as a human-exosuit biomechanical model to elucidate how individual design parameters affect exosuit assistance torque and device-to-body forces. The proof-of-concept prototype, case study, and modeling work provide a foundation for understanding and implementing extensible exosuits for a broad range of applications. We envision promising opportunities to apply this new dual-mode extensible exosuit concept to assist heavy-lifting, to further enhance user comfort, and to address the unique needs of last-mile delivery workers.

Low-profile elastic exosuit reduces back muscle fatigue.

We investigated the extent to which an un-motorized, low-profile, elastic exosuit reduced the rate of fatigue for six lumbar extensor muscles during leaning. Six healthy subjects participated in an A-B-A (withdrawal design) study protocol, which involved leaning at 45º for up to 90 s without exosuit assistance (A1), then with assistance (B), then again without assistance (A2). The exosuit provided approximately 12-16 Nm of lumbar extension torque. We measured lumbar muscle activity (via surface electromyography) and assessed fatigue rate via median frequency slope. We found that five of the six subjects showed consistent reductions in fatigue rate (ranging from 26% to 87%) for a subset of lumbar muscles (ranging from one to all six lumbar muscles measured). These findings objectively demonstrate the ability of a low-profile elastic exosuit to reduce back muscle fatigue during leaning, which may improve endurance for various occupations.

Subject-specific responses to an adaptive ankle prosthesis during incline walking.

Individuals with lower-limb amputation often have difficulty walking on slopes, in part due to limitations of conventional prosthetic feet. Conventional prostheses have fixed ankle set-point angles and cannot fully replicate able-bodied ankle dynamics. Microprocessor-controlled ankles have been developed to help overcome these limitations. The objective of this study was to characterize how the slope adaptation feature of a microprocessor-controlled ankle affected individual prosthesis user gait biomechanics during sloped walking. Previous studies on similar microprocessor-controlled ankles have focused on group-level results (inter-subject mean), but did not report individual subject results. Our study builds upon prior work and provides new insight by presenting subject-specific results and investigating to what extent individual responses agree with the group-level results. We performed gait analysis on seven individuals with unilateral transtibial amputation while they walked on a 7.5° incline with a recently redesigned microprocessor-controlled ankle that adjusts ankle set-point angle to the slope. We computed gait kinematics and kinetics, and compared how users walked with vs. without this set-point adjustment. The microprocessor-controlled ankle increased minimum toe clearance for all subjects. Despite the microprocessor-controlled ankle behaving similarly for each user, we observed marked differences in individual responses. For instance, two users switched from a forefoot landing pattern with the microprocessor-controlled ankle locked at neutral angle to rearfoot landing when the microprocessor-controlled ankle adapted to the slope, while two maintained a forefoot and three maintained a rearfoot landing pattern across conditions. Changes in knee angle and moment were also subject-specific. Individual user responses were often not well represented by inter-subject mean. Although the prevailing experimental paradigm in prosthetic gait analysis studies is to focus on group-level analysis, our findings call attention to the high inter-subject variability which may necessitate alternative experimental approaches to assess prosthetic interventions.

Feasibility of a Biomechanically-Assistive Garment to Reduce Low Back Loading During Leaning and Lifting.

GOAL: The purpose of this study was: 1) to design and fabricate a biomechanically-assistive garment which was sufficiently lightweight and low-profile to be worn underneath, or as, clothing, and then 2) to perform human subject testing to assess the ability of the garment to offload the low back muscles during leaning and lifting. METHODS: We designed a prototype garment which acts in parallel with the low back extensor muscles to reduce forces borne by the lumbar musculature. We then tested eight healthy subjects while they performed common leaning and lifting tasks with and without the garment. We recorded muscle activity, body kinematics, and assistive forces. RESULTS: The biomechanically-assistive garment offloaded the low back muscles, reducing erector spinae muscle activity by an average of 23-43% during leaning tasks, and 14-16% during lifting tasks. CONCLUSION: Experimental findings in this study support the feasibility of using biomechanically-assistive garments to reduce low back muscle loading, which may help reduce injury risks or fatigue due to high or repetitive forces. SIGNIFICANCE: Biomechanically-assistive garments may have broad societal appeal as a lightweight, unobtrusive, and cost-effective means to mitigate low back loading in daily life.