The effect of arm weight support on upper limb muscle synergies during reaching movements

Abstract

Background: Compensating for the effect of gravity by providing arm-weight support (WS) is a technique often utilized in the rehabilitation of patients with neurological conditions such as stroke to facilitate the performance of arm movements during therapy. Although it has been shown that, in healthy subjects as well as in stroke survivors, the use of arm WS during the performance of reaching movements leads to a general reduction, as expected, in the level of activation of upper limb muscles, the effects of different levels of WS on the characteristics of the kinematics of motion and of the activity of upper limb muscles have not been thoroughly investigated before. Methods: In this study, we systematically assessed the characteristics of the kinematics of motion and of the activity of 14 upper limb muscles in a group of 9 healthy subjects who performed 3-D arm reaching movements while provided with different levels of arm WS. We studied the hand trajectory and the trunk, shoulder, and elbow joint angular displacement trajectories for different levels of arm WS. Besides, we analyzed the amplitude of the surface electromyographic (EMG) data collected from upper limb muscles and investigated patterns of coordination via the analysis of muscle synergies. Results: The characteristics of the kinematics of motion varied across WS conditions but did not show distinct trends with the level of arm WS. The level of activation of upper limb muscles generally decreased, as expected, with the increase in arm WS. The same eight muscle synergies were identified in all WS conditions. Their level of activation depended on the provided level of arm WS.

Design and Performance Evaluation of a Wearable Passive Cable-driven Shoulder Exoskeleton

“…Even when only compensating for one-fourth of the gravity moment, the WPCSE promisingly reduced the average (ranging from 9% to 35%) and peak (ranging from 10% to 33%) neuromuscular activity of several muscles crossing the shoulder during positive shoulder elevation/adduction. Our results are consistent with several previous studies that also showed that varying levels of gravity compensation at the shoulder can reduce muscle activity [8,9,36,37].…”

Exoskeleton for Gait Rehabilitation: Effects of Assistance, Mechanical Structure, and Walking Aids on Muscle Activations

“…In order to simplify the comparison of the muscle synergies among conditions, the same number of muscle synergies was retained within the same condition across participants; the number was established as the rounded average across participants [33,38]. The NNMF algorithm does not extract muscle synergies in the same order for each subjects and different walking modalities.…”

Motor improvement estimation and task adaptation for personalized robot-aided therapy: a feasibility study

“…Using the robotic upper limb exoskeleton ALEx [39, 40], we designed a three-dimensional point-to-point reaching task (Fig. 1a-b), a training exercise commonly used in robotic rehabilitation therapy [41–43]. In order to challenge the subjects and make them adapt to a new motor control scheme with temporal dynamics similar to those observed in robot-aided rehabilitation of stroke patients, the visual feedback was manipulated during five inversion blocks B 1-5 (Fig.…”

“…Using the robotic upper limb exoskeleton ALEx [39, 40], we designed a three-dimensional point-to-point reaching task, a training exercise commonly used in robotic rehabilitation therapy [41–43]. The movement amplitude was selected to allow the exploration of a functional workspace, while movement directions were chosen to elicit independent and synergistic motion of shoulder and elbow, capitalizing on the advantages provided by robotic exoskeleton devices [51].…”