A Computational Index to Describe Slacking During Robot Therapy.

Movement facilitation has a fundamental role in the rehabilitation treatment of stroke survivors. However, its action mechanisms are still poorly understood. An open question is to identify the effect of the level of assistance on the recovery process. To address this topic, new insight on voluntary control and movement strategies during rehabilitation must be gained. Robot-assisted arm movements were examined in a task where subjects had to reach distal targets in the presence of assistive forces. As the training proceeded, subjects improved their performance and exercised with both the initial force level of the first session and with progressively decreasing levels of assistive force. We found that when stroke survivors became to execute voluntary movements with lower forces levels they decreased their voluntary control in the presence of higher forces, following a minimum effort trajectory. These findings provide a new important insight for the rehabilitation of stroke survivors, suggesting that passive mobilization and exercise with constant force, although useful for muscular reinforcement, may have a detrimental effect on voluntary control and movements planning.