This paper presents an underwater lower-extremity soft exoskeleton which could provide assistance to swimming motions. With this motivation, we designed an exoskeleton called Powered Swimsuit to assist the wearer in breaststroke with fins. The actuation system was embedded inside of a portable waterproof cabin fabricated on the back of the swimsuit. The assistive force was applied to the bottom of the fins via soft cables. During the propelling period of the stroke cycle, the cables pulled the ankle joints to provide assistance to plantar flexion. Three competitive swimmers participated the experiments to evaluate the proposed soft exoskeleton. Several kinematic parameters including joint angles and muscle activities of the lower extremities were recorded simultaneously. Compared with breaststroke without assistance, the peak of surface electromyography in the sweep phase with the exoskeleton assistance decreased by 49.13% (gastrocnemius) and 74.51% (soleus) on an average. The results showed the feasibility of the proposed Powered Swimsuit in underwater motion assistance.

Gait asymmetry due to the loss of unilateral limb increases the risk of injury or progressive joint degeneration. The development of wearable robotic devices paves a way to improve gait symmetry of unilateral amputees. Moreover, the state-of-the-art studies on human-in-the-loop optimization strategies through decreasing the metabolic cost as the optimization task, have met several challenges, e.g. too long period of optimization and the optimization feasibility for unilateral amputees who have the deficit of gait symmetry. Here, in this paper, we proposed gait-symmetry-based human-in-the-loop optimization method to decrease the risk of injury or progressive joint degeneration for unilateral transtibial amputees. The experimental results (N = 3 unilateral transtibial subjects) demonstrate that only average 9.0±4.1min of convergence was taken. Compared to gait symmetry while wearing prosthetics, after optimization, the gait symmetry indicator value of the subjects wearing the robotic prostheses was improved by 21.0% and meanwhile the net metabolic energy consumption value was reduced by 9.2%. Also, this paper explores the rationality of gait indicators and what kind of gait indicators are the optimization target. These results suggest that gait-symmetry-based human-in-the-loop strategy could pave a practical way to improve gait symmetry by accompanying the reduction of metabolic cost, and thus to decrease the risk of joint injury for the unilateral amputees. KeywordsHuman-in-the-loop, gait symmetry, metabolic cost, unilateral transtibial amputees, robotic prostheses metabolic cost rate. Moreover, few studies of human-inthe-loop focused on the unilateral amputees, who had the consequences of gait symmetry.Biological studies show that due to the loss of lower limb, the amputees exhibited the gait asymmetry in kinetics and kinematics, compared to the able-bodied Sanderson and Martin (1997). For the unilateral amputees, this kind of gait asymmetry influences the maximum torque and torque steadiness significantly in the intact leg in some extents Simoneau-Buessinger et al. (2019). The reason for gait asymmetry maybe mainly resulted from strength asymmetry Lloyd et al. (2010), during walking. Strength asymmetry in unilateral transtibial amputees has a moderate relationship in an increased risk of developing osteoarthritis Lloyd et al. (2010). For the transtibial amputees, the walking speed also influenced gait symmetry Nolan et al. (2003). During jumping landing, peak force asymmetry and moment asymmetry may potentially be easy to result in injury or progressive joint degeneration for transtibial amputees and improving gait symmetry in jumping is

Gait asymmetry due to the loss of unilateral limb increases the risk of injury or progressive joint degeneration. The development of wearable robotic devices paves a way to improve gait symmetry of unilateral amputees. Moreover, the state-of-the-art studies on human-in-the-loop optimization strategies through decreasing the metabolic cost as the optimization task, have met several challenges, e.g. too long period of optimization and the optimization feasibility for unilateral amputees who have the deficit of gait symmetry. Here, in this paper, we proposed gait-symmetry-based human-in-the-loop optimization method to decrease the risk of injury or progressive joint degeneration for unilateral transtibial amputees. The experimental results (N = 3 unilateral transtibial subjects) demonstrate that only average 9.0±4.1min of convergence was taken. Compared to gait symmetry while wearing prosthetics, after optimization, the gait symmetry indicator value of the subjects wearing the robotic prostheses was improved by 21.0% and meanwhile the net metabolic energy consumption value was reduced by 9.2%. Also, this paper explores the rationality of gait indicators and what kind of gait indicators are the optimization target. These results suggest that gait-symmetry-based human-in-the-loop strategy could pave a practical way to improve gait symmetry by accompanying the reduction of metabolic cost, and thus to decrease the risk of joint injury for the unilateral amputees.