400 Section - Muscle activity analysis during training using HAL in patients with shoulder motion impairment due to cervical disorder: a frequency domain approach

Objectives : Recently, we have reported shoulder motion training using the single-joint HAL (Hybrid Assistive Limb, Cyberdyne) for shoulder movement disorders such as postoperative C5 palsy after cervical spine surgery, as well as the resulting improvements in motor function (Kubota et al., 2023). We also reported that, during HAL-assisted training, compensatory activity of the trapezius muscle is reduced, enabling shoulder elevation based on activation of the deltoid—the primary agonist—which may represent an underlying kinematic mechanism of the improvement after training (Lafitte et al., 2022). To further investigate changes in muscle control during HAL use, we conducted a frequency-domain analysis of muscle activity.

Design: We analyzed 10 patients with shoulder movement disorders due to cervical spine pathology who underwent shoulder joint training with HAL. The mean number of training sessions was 13.6 (range: 10–23). In each session, surface EMG (Electromyography, Delsys Trigno Lab, 2 kHz) was recorded for both with HAL and without HAL conditions. From these data, we extracted integrated EMG (iEMG 200ms moving window), mean frequency, median frequency, and normalized mean frequency (mean frequency normalized by integrated EMG). Comparisons were conducted using a generalized linear mixed model with a significance level of p < 0.05.

Results: For the deltoid muscle, mean frequency, median frequency, and normalized mean frequency increased during HAL use by 9.3%, 7.7%, and 57% respectively. For the trapezius muscle, iEMG reduced by 48.2% and only normalized mean frequency increased by 219% during HAL use.

Conclusion: Frequency measures increased during HAL use for the deltoid muscle, and the frequency measure normalized by power also increased for the trapezius muscle. These increases may indicate enhanced recruitment of motor units during HAL-assisted movement. By providing joint assistance that reflects the user’s motor intention and reducing mechanical load during training, HAL may facilitate sensorimotor neural activation and contribute to motor learning.