Characteristics of muscle activity and joint dynamics during weight lifting by isotonic elbow flexion with assistive force

Abstract

[Objectives] This study focused on submaximal weightlifting (stopping at a targeted height) by elbow flexion and investigated the differences in muscle activity and joint dynamics under assisted and unassisted conditions. [Methods] Eight young adults lifted weights (equivalent to 15% of the biceps maximal voluntary contraction [MVC]) by isotonic elbow flexion with and without assistive force using our originally developed impedance-controlled assistive devices. The participants lifted weights to achieve a reference target on the screen (the angular position of the wrist) and terminated the movement at the specified target stopping position. During the task, we measured the dynamics of the elbow joint movement, as well as the co-contraction index of the biceps brachii (BB) and triceps brachii (TB) using electromyography (EMG). [Results and Discussion] The rectified EMG waveforms for the BB and TB exhibited a bimodal and unimodal waveform under the assisted and unassisted conditions, respectively. Under the assisted condition, the elbow joint angle tended to overshoot the target stopping position, suggesting that additional effort was required to accurately terminate the elbow flexion. [Conclusion] It was suggested that although humans could use an assistive force to reduce the muscle load, they have unique motor control to maintain joint movement accuracy.

Keywords: Exoskeleton, Assistive Technology, Man-Machine Cooperation

DOI: 10.54941/ahfe1005173