*Communication* **Electromyography–Force Relation and Muscle Fiber Conduction Velocity Affected by Spinal Cord Injury**

**Le Li 1,† , Huijing Hu 1,† , Bo Yao 2 , Chengjun Huang 3 , Zhiyuan Lu 4 , Cliff S. Klein <sup>5</sup> and Ping Zhou 4, \***


**Abstract:** A surface electromyography (EMG) analysis was performed in this study to examine central neural and peripheral muscle changes after a spinal cord injury (SCI). A linear electrode array was used to record surface EMG signals from the biceps brachii (BB) in 15 SCI subjects and 14 matched healthy control subjects as they performed elbow flexor isometric contractions from 10% to 80% maximum voluntary contraction. Muscle fiber conduction velocity (MFCV) and BB EMG–force relation were examined. MFCV was found to be significantly slower in the SCI group than the control group, evident at all force levels. The BB EMG–force relation was well fit by quadratic functions in both groups. All healthy control EMG–force relations were best fit with positive quadratic coefficients. In contrast, the EMG–force relation in eight SCI subjects was best fit with negative quadratic coefficients, suggesting impaired EMG modulation at high forces. The alterations in MFCV and EMG–force relation after SCI suggest complex neuromuscular changes after SCI, including alterations in central neural drive and muscle properties.

**Keywords:** spinal cord injury (SCI); muscle fiber conduction velocity (MFCV); surface electromyography (EMG); EMG–force relation
