Hemiplegia affects the biomechanics of reaching with the unaffected upper limb

Objective To analyze the bio-mechanics when hemiplegics reach with the unaffected upper limb. Methods Thirty post-stroke hemiplegics were selected into the patient group, while 23 healthy counterparts were chosen for the control group. Both groups completed a reaching test of their upper limbs which divided reaching into a moving stage and a holding stage. Surface electromyography (sEMG) data were recorded during the tests along with the degree of torso twist, the range of motion of the shoulder, movement velocity, smoothness of movement and angle divergence collected using a wearable micro-sensor motion capture system. Results For the stroke patients whose dominant upper limb was unaffected, the average root mean square (RMS) signal from the upper trapezius (34.3 μV) and the average torso twist (-1.4°) in the moving phase were significantly larger than among the control subjects (19.7 μV and -2.3°), but their average movement velocity was significantly slower. In the holding phase the average RMS signal from the upper trapezius (55.4 μV) was still significantly higher than in the control group, but their average pectoralis major signal and the integrated EMG ratio of the anterior segments of the deltoid and upper trapezius muscle pairs were significantly lower. For the stroke patients whose dominant upper limbs were affected, in the moving phase their average signal from the middle segments of the deltoid were significantly greater than those of the controls, but their movement velocity was significantly slower. For the control subjects, in the moving phase the average signal from the upper trapezius on their non-dominant side was significantly higher than that from the dominant upper limb. The integrated EMG ratio from the anterior segments of the deltoid and upper trapezius muscle pairs on that side was smaller throughout the whole reaching movement. Conclusion The bio-mechanical characteristics in reaching of the unaffected upper limbs of stroke patients are not the same as those of the corresponding upper limbs of healthy subjects. It is more reasonable to select the corresponding upper limbs of healthy subjects as controls when a bio-mechanical study of the affected upper limbs is conducted. Key words: Stroke; Reaching; Kinematics; Electromyography