Muscle Activity In Upper Extremity Is Modulated During Arm Cycling Exercises After Cervical Spinal Cord Injuries

Abstract

Regaining upper extremity function following spinal cord injury (SCI) is one of the most important outcomes for quadriplegics with regards to enhancing quality of life. To facilitate locomotor recovery through increased activation of the lower limb muscles, ground reaction forces are commonly manipulated to optimal levels. Using similar mechanisms, manipulating power production during arm cycling exercises could facilitate activation of the upper limb muscles after SCI. PURPOSE: To determine if upper limb muscles activation is modulated during arm cycling exercises after SCI. METHODS: Five participants with chronic SCI at C4; classified as AIS A (1), B (2), C (1) and D (1) according to the American Spinal Injury Association Impairment Scale performed arm cycling exercises at four power levels (0, 5, 10, 15W) with their hands securely attached to the handles. Surface EMG signals were recorded during a series of 10 consecutive cycles from one muscle above the lesion: medial trapezius (C2-C4); and six muscles below the lesion: deltoid posterior (C5-C6), biceps brachialis (C5-C6), triceps brachialis (C6-C8), extensor digitorum (C6-C8), flexor carpi radialis (C6-C8) and extensor carpi radialis (C6-C8). RESULTS: Arm cycling exercises were successfully performed at cadences ranging from 30 to 50 rpm. EMG signals were detected in all muscles from all participants. Modulation of EMG signals within the cycle was seen in most exercise conditions and participants, while modulation was most identifiable when participants produced larger levels of power. Increasing power production from 0 to 15 W led to an increase in the peak EMG activity of the trapezius muscle, as well as in four muscles below the lesion: deltoid, biceps and triceps brachialis, and extensor carpi radialis (P < 0.05). CONCLUSIONS: Participants of all levels of impairment successfully performed the arm cycling exercises. Increasing power production up to 15W improved modulation of EMG signals during the cycle and increased activation of some muscles below the lesion, crossing the shoulder, elbow and wrist joints. Including arm cycling exercises in rehabilitation programs should be considered to take advantage of spinal circuitry available below the level of injury and facilitate the recovery of upper extremity function after SCI.