Effect of timing of hip extension assistance during loaded walking with a soft exosuit

Abstract

BackgroundRecent advances in wearable robotic devices have demonstrated the ability to reduce the metabolic cost of walking by assisting the ankle joint. To achieve greater gains in the future it will be important to determine optimal actuation parameters and explore the effect of assisting other joints. The aim of the present work is to investigate how the timing of hip extension assistance affects the positive mechanical power delivered by an exosuit and its effect on biological joint power and metabolic cost during loaded walking. In this study, we evaluated 4 different hip assistive profiles with different actuation timings: early-start-early-peak (ESEP), early-start-late-peak (ESLP), late-start-early-peak (LSEP), late-start-late-peak (LSLP).MethodsEight healthy participants walked on a treadmill at a constant speed of 1.5 m · s-1 while carrying a 23 kg backpack load. We tested five different conditions: four with the assistive profiles described above and one unpowered condition where no assistance was provided. We evaluated participants’ lower limb kinetics, kinematics, metabolic cost and muscle activation.ResultsThe variation of timing in the hip extension assistance resulted in a different amount of mechanical power delivered to the wearer across conditions; with the ESLP condition providing a significantly higher amount of positive mechanical power (0.219 ± 0.006 W · kg-1) with respect to the other powered conditions. Biological joint power was significantly reduced at the hip (ESEP and ESLP) and at the knee (ESEP, ESLP and LSEP) with respect to the unpowered condition. Further, all assistive profiles significantly reduced the metabolic cost of walking compared to the unpowered condition by 5.7 ± 1.5 %, 8.5 ± 0.9 %, 6.3 ± 1.4 % and 7.1 ± 1.9 % (mean ± SE for ESEP, ESLP, LSEP, LSLP, respectively).ConclusionsThe highest positive mechanical power delivered by the soft exosuit was reported in the ESLP condition, which showed also a significant reduction in both biological hip and knee joint power. Further, the ESLP condition had the highest average metabolic reduction among the powered conditions. Future work on autonomous hip exoskeletons may incorporate these considerations when designing effective control strategies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12984-016-0196-8) contains supplementary material, which is available to authorized users.

Influence of Power Delivery Timing on the Energetics and Biomechanics of Humans Wearing a Hip Exoskeleton

“…Recent work with hip and ankle exoskeletons has focused on the goal of reducing the metabolic cost of walking, and researchers have succeeded in a number of experiments (Ronsse et al, 2011; Mooney et al, 2014; Ding et al, 2016a,b; Ruiz Garate et al, 2016; Seo et al, 2016). Research groups have used both rigid exoskeletons (Ruiz Garate et al, 2016), as we use in our experiment, and soft exoskeletons to test the effect of different hip assistance strategies on metabolic output (Ding et al, 2016a; Panizzolo et al, 2016).…”

Human Factors Considerations for Enabling Functional Use of Exosystems in Operational Environments

“…Inappropriate mappings between these underlying models can cause reduction in performance and increase in the frequency and magnitude of errors due to confusion, distraction, and concerns for safety [37], [38]. Zhang et al [39] and Ding et al [40] have shown that different control methods and timings of active assistance altered human performance. It may be that certain control mappings better align with the operator's mental model across goals or behaviors, yielding improved performance and the ability to develop improved skill-based behaviors.…”

“…As previously mentioned, the less the user must directly input and control, the better for synergy and ability to engage with the surroundings. However, the selection of the underlying controller impacts the kinematics and metabolic consumption (e.g., [40], [58]- [60]). The actuation timings are important for enabling efficient mode transitions such that systems do not have a sluggish response or disturb the desired biomechanics.…”

Robotic hip-disarticulation prosthesis: evaluation of prosthetic gaits in a non-amputee individual

“…Moreover, assistance of the hip joint also may improve gait in amputees, because assisted hip motion was found to not only improve spatiotemporal gait parameters, i.e. velocity, cadence, step time, stance time, swing time, double support time, stride length and spatial asymmetry in stroke survivors [13], but also to reduce the metabolic cost during walking in healthy subjects [14].…”