An explorative study into changes in circle drawing after gravity compensation training in chronic stroke patients.

A way to reduce the influence of abnormal synergies on range of motion after stroke directly is to support the arm by a robotic gravity compensation device. However, it is not known whether a period of training with arm support improves independent, unsupported circle drawing, and what the role of abnormal synergies is. Seven chronic stroke patients received three 30 minute robotic gravity compensation training sessions per week for a period of six weeks. During baseline and evaluation measurements, Fugl-Meyer (FM) scores and circle drawing performance (area and roundness) were determined. After training, FM had improved in some subjects. Circle area increased significantly across subjects, whereas roundness did not. This indicates an improved unsupported active range of motion, but the influence of (reduced) abnormal synergies on this change remains unclear. Despite the small number of subjects, the present explorative study suggests that robotic gravity compensation training has the potential to increase the work area of the affected arm of chronic stroke patients. Further research into the impact of robotic gravity compensation training is warranted, to enhance insight into underlying mechanisms and optimal applications in clinical practice.

Influence of gravity compensation on muscle activation patterns during different temporal phases of arm movements of stroke patients.

BACKGROUND: Arm support to help compensate for the effects of gravity may improve functional use of the shoulder and elbow during therapy after stroke, but gravity compensation may alter motor control. OBJECTIVE: To obtain quantitative information on how gravity compensation influences muscle activation patterns during functional, 3-dimensional reaching movements. METHODS: Eight patients with mild hemiparesis performed 2 sets of repeated reach and retrieval movements, with and without unloading the arm, using a device that acted at the elbow and forearm to compensate for gravity. Electromyographic (EMG) patterns of 6 upper extremity muscles were compared during elbow and shoulder joint excursions with and without gravity compensation. RESULTS: Movement performance was similar with and without gravity compensation. Smooth rectified EMG (SRE) values were decreased from 25% to 50% during movements with gravity compensation in 5 out of 6 muscles. The variation of SRE values across movement phases did not differ across conditions. CONCLUSIONS: Gravity compensation did not affect general patterns of muscle activation in this sample of stroke patients, probably since they had adequate function to complete the task without arm support. Gravity compensation did facilitate active arm movement excursions without impairing motor control. Gravity compensation may be a valuable modality in conventional or robot-aided therapy to increase the intensity of training for mildly impaired patients.

Influence of gravity compensation on muscle activity during reach and retrieval in healthy elderly.

INTRODUCTION: Arm support like gravity compensation may improve arm movements during stroke rehabilitation. It is unknown how gravity compensation affects muscle activation patterns during reach and retrieval movements. Since muscle activity during reach is represented by a component varying with movement velocity and a component supposedly counteracting gravity, we hypothesized that gravity compensation decreases the amplitude of muscle activity, but does not affect the pattern. To examine this, we compared muscle activity during well defined movements with and without gravity compensation in healthy elderly. METHODS: Ten subjects performed reach and retrieval movements with and without gravity compensation. Muscle activity of biceps, triceps, anterior, middle and posterior parts of deltoid and upper trapezius was compared between the two conditions. RESULTS: The level of muscle activity was lower with gravity compensation in all muscles, reaching significance in biceps, anterior deltoid and trapezius (p < or = 0.026). The muscle activation pattern did not differ between movements with and without gravity compensation (p > or = 0.662). DISCUSSION: Gravity compensation only influenced the level of muscle activity but not the muscle activation pattern in terms of timing. Future studies should examine if the influence of gravity compensation is comparable for stroke patients. This may stimulate early and intensive training during rehabilitation.