Lowering locomotion's metabolic cost: Walking and running require different gaits, with each type of motion putting a greater bias on different muscles and joints. Kim et al. developed a soft, fully portable, lightweight exosuit that is able to reduce the metabolic rate for both running and walking by assisting each motion via the hip extension (see the Perspective by Pons). A waist belt holds most of the mass, thus reducing the cost of carrying the suit. By tracking the motion of the user, the suit is able to switch modes between the two types of motion automatically. Science , this issue p. 668 ; see also p. 636

A tethered exosuit reduces the metabolic cost of running.

This study presents the design of a lower limb-worn, soft wearable robot that assists ankle plantar flexion using soft textiles and a shape memory alloy (SMA) wire actuator. Textile-based clothing-type soft wearable robots, the smart clothes in short, are proposed to build a soft exoskeleton that is inherently lightweight and comfortable for the wearer. SMA wire actuators are embedded in the smart clothes to provide assistive forces to the wearer. The SMA wire actuator is a low-profile wire-type artificial muscle actuator, which can be embedded on the textile without any extruded parts on the clothing. We have built an SMA wire actuator-embedded smart clothing that is able to provide ankle assistive force without rigid kinematic mechanisms. The smart clothing has a mass of 428.5 g without a power battery, and it can generate an ankle moment of 100 N cm in each ankle during walking.

The use of wearable robots to provide walking assistance has rapidly grown over the past decade, with notable advances made in robot design and control methods toward reducing physical effort while performing an activity. The reduction in walking effort has mainly been achieved by assisting forward progression in the sagittal plane. Human gait, however, is a complex movement that combines motions in three planes, not only the sagittal but also the transverse and frontal planes. In the frontal plane, the hip joint plays a key role in gait, including balance. However, wearable robots targeting this motion have rarely been investigated. In this study, we developed a hip abduction assistance wearable robot by formulating the hypothesis that assistance that mimics the biological hip abduction moment or power could reduce the metabolic cost of walking and affect the dynamic balance. We found that hip abduction assistance with a biological moment second peak mimic profile reduced the metabolic cost of walking by 11.6% compared with the normal walking condition. The assistance also influenced balance-related parameters, including the margin of stability. Hip abduction assistance influenced the center-of-mass movement in the mediolateral direction. When the robot assistance was applied as the center of mass moved toward the opposite leg, the assistance replaced some of the efforts that would have otherwise been provided by the human. This indicates that hip abduction assistance can reduce physical effort during human walking while influencing balance.