Impact of Exoskeleton Support on Discharge Statistics of Motor Units During Quasi-Isometric Tasks

The industry 5.0 paradigm emphasizes a human-centric approach to industrial processes, integrating technology to optimize safety, ergonomics, and productivity. Among these technologies, exoskeletons have emerged as promising tools for alleviating physical strain during labor-intensive tasks. While previous research has focused on the impact of exoskeletons on muscle activation, biomechanics, and metabolism, their effects on the neuromuscular system remain unexplored. This pilot study aimed at testing a protocol to investigate the influence of a hybrid exoskeleton on neuromuscular control during quasi-isometric tasks at varying mechanical loads and support levels. High-Density Surface Electromyography (HDsEMG) and single motor unit (MU) analysis were used to assess changes in MU discharge rate and discharge rate variability in the biceps brachii and anterior deltoid muscles. A single participant performed tasks involving holding 4 kg and 8 kg loads, both with and without exoskeleton assistance, where support levels were calibrated at 75% (for the 4 kg load) and at 50% and 75% (for the 8 kg load). Results showed that during the 4 kg task, MU discharge characteristics were stable in the biceps, while the deltoid exhibited a decrease in discharge rate and an increase in variability. For the 8 kg task with 50% and 75% support, biceps MU discharge remained consistent, but the deltoid showed a further decrease in discharge rate and increased variability, especially at 75% support. These preliminary results show that HDsEMG can be used to analyze the influence of an exoskeleton on neuromuscular control and indicate that exoskeletons can alter neural control strategies.