These results suggest the HTS is effective for alleviating pain and improving physical performance in women with risk factors for knee OA. However, the HTS does not appear to be superior to low-load resistance training for improving muscle strength, pain relief, or physical function. This clinical trial was registered at clinicaltrials.gov (study ID NCT02802878).

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Background & Rationale Osteoarthritis of the knee (KOA) is the most common cause of disability not only in the United States but also in Japan. KOA is associated with pain, quadriceps weakness, swelling, instability, decline of range of motion, physical function, and quality of life (QOL) (1). In particular, quadriceps weakness may contribute to incident symptomatic and progressive disease (2, 3), cause functional limitations and disability (4) and increase the risk of mortality (5). Both aerobic exercise and resistance exercise are recommended for the treatment of people with knee osteoarthritis (KOA) (6). However, exercise at a moderate or severe intensity is often a problem for people with knee pain or a history of knee injury. Neuromuscular electrical stimulation (NMES) is widely used as a method to increase muscle strength and improve physical function even at a low-moderate exercise intensity (7). However, NMES effect may prove to be insufficient because the exercise intensity is determined by the electrical stimulation endurance level of the user (7). On the other hand, transcutaneous electrical stimulation, so-called transcutaneous electrical nerve stimulation (TENS), is effective for pain relief (8). Knee pain independently reduced quadriceps strength and activation (9). TENS restores inhibited quadriceps motor function (central and muscle activation) through pain relief (10). Moreover the combined application of electrical stimulation (ES) and volitional contractions (VC) is said to be more effective than ES or VC alone (11). Therefore, a hybrid training system (HTS) that resists the motion of a volitionally contracting agonist muscle using the force generated by its electrically stimulated antagonist (NMES) was developed as a way to combine the application of electrical stimulation and voluntary contraction (12). HTS is a method that eliminates the disadvantages of both volitional exercise and NMES (13). It has been reported that HTS is a new training technique that can increase both muscular strength and muscle mass (12, 13, 14, 15). Recently, HTS is showing promise as a countermeasure for the musculoskeletal disuse of astronauts because the HTS technique can generate exercise resistance within the body even if there is no gravity (1). In addition, we can utilize HTS during many different types of exercise (e.g. knee extension exercise, squat and hip flexion, walking exercise, and cycling exercise) (17, 18). It seems to be more effective for improvement of muscle strength and physical function to combine HTS with easy exercise (e.g. knee extension, walking, and squats) for KOA patients. The main purpose of exercise therapy for KOA is not only muscular strength improvement (the quadriceps femoris muscle in particular) and but also pain relief (19, 20). Muscular strength improvement protects joints and relieves nociceptive stimulation. However, exercise sometimes increases pain. In addition to the pathological change in articular structures, changes in central pain processing or central sensitization ap...

Research on robotic lower-limb assistive devices over the past decade has generated autonomous, multiple degree-of-freedom devices to augment human performance during a variety of scenarios. However, the increase in capabilities of these devices is met with an increase in the complexity of the overall control problem and requirement for an accurate and robust sensing modality for intent recognition. Due to its ability to precede changes in motion, surface electromyography (EMG) is widely studied as a peripheral sensing modality for capturing features of muscle activity as an input for control of powered assistive devices. In order to capture features that contribute to muscle contraction and joint motion beyond muscle activity of superficial muscles, researchers have introduced sonomyography, or real-time dynamic ultrasound imaging of skeletal muscle. However, the ability of these sonomyography features to continuously predict multiple lower-limb joint kinematics during widely varying ambulation tasks, and their potential as an input for powered multiple degree-of-freedom lower-limb assistive devices is unknown. The objective of this research is to evaluate surface EMG and sonomyography, as well as the fusion of features from both sensing modalities, as inputs to Gaussian process regression models for the continuous estimation of hip, knee and ankle angle and velocity during level walking, stair ascent/descent and ramp ascent/descent ambulation. Gaussian process regression is a Bayesian nonlinear regression model that has been introduced as an alternative to musculoskeletal model-based techniques. In this study, time-intensity features of sonomyography on both the anterior and posterior thigh along with time-domain features of surface EMG from eight muscles on the lower-limb were used to train and test subject-dependent and task-invariant Gaussian process regression models for the continuous estimation of hip, knee and ankle motion. Overall, anterior sonomyography sensor fusion with surface EMG significantly improved estimation of hip, knee and ankle motion for all ambulation tasks (level ground, stair and ramp ambulation) in comparison to surface EMG alone. Additionally, anterior sonomyography alone significantly improved errors at the hip and knee for most tasks compared to surface EMG. These findings help inform the implementation and integration of volitional control strategies for robotic assistive technologies.

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