Surface EMG Analysis During The Upper Limb Reach-to-grasp Process In Patients With C5/6 Spinal Cord Injuries

Objectives The objective of this study was to investigate and compare the muscle utilization ratio(MUR)and co-activation ratios(CR)during a reach-to-grasp task in patients with C5 or C6 spinal cord injury(SCI)and find a possible correlation between the muscle utilization ratio(MUR)and functional scale.Methods Ten C5/6 SCI patients and 10 healthy controls were recruited to perform a reach and retrieval task.All SCI patients were evaluated spinal cord independence measure(SCIM-III).Surface electromyography(s EMG)activity of seven major upper limb muscles(the upper part of the pectoralis major,the deltoid anterior and posterior,the biceps brachii,the triceps brachii,the flexor carpi radialis and the extensor carpi radialis)were recorded.The MUR means the amplitude of each s EMG signal recorded normalized by peak EMG values recorded during 3-s static maximal voluntary contractions(MVCs)performed against gravity and resistance according to a standardized protocol.The co-activation ratios(CR)for the joint were calculated as a ratio of the difference between mean joint flexor EMG activity and mean joint extensor EMG activity over the sum of the mean flexor and extensor EMG activities.MUR for each muscle were analyzed between and within the two groups,CR for each muscle were analyzed between two groups,and correlations between MUR and clinical scale were analyzed.Results(1)it was revealed that the MVC of TB,FCR and ECR were lower in the SCI than the control(p < 0.05).(2)The MUR had a significant difference both in groups and muscles(p < 0.05).Within the control group,the MUR of UPM and PD were lower than AD(p < 0.05);within the SCI group,the MUR of UPM,PD and AD had no significant difference(p > 0.05),it was indicated that UPM and PD in proximal muscles compensated in C5/6 SCI patients.(3)The CR of the elbow was higher than control group(p<0.05).(4)There was a negative correlation between the MUR and SCIM-III scores.Conclusion(1)This study showed that C5/6 SCI patients could complete the same task with different motor strategy,changes in activation patterns of motor units(MU recruitment,MU firing rates),and altered coordination patterns in central nervous system may be the reason.(2)The flexor muscle of elbow activated obviously in C5/6 SCI patients,it indicated that rehabilitation intervention need to be emphasized in the early post injury phase in order to prevent the joint contracture.(3)The negative correlation between the MUR and functional assessment indicated that the s EMG could be an objective and quantitative measurement used in hospital settings.The study findings could help provide a theoretical basis and new directions for clinical rehabilitation.