Torque and mechanomyogram relationships during electrically-evoked isometric quadriceps contractions in persons with spinal cord injury. Issue 8 (August 2016)

• Record Type: Journal Article
• Authors: Ibitoye, Morufu Olusola; Hamzaid, Nur Azah; Hasnan, Nazirah; Abdul Wahab, Ahmad Khairi; Islam, Md. Anamul; Kean, Victor S.P.; Davis, Glen M.
• Is Part Of: Medical engineering & physics. Volume 38:Issue 8(2016:Aug.)
• Page Start: 767
• Page End: 775
• Publication Date: 2016-08
• Subjects: Mechanomyogram -- Spinal cord injury -- NMES-evoked muscle contractions -- Muscle torque -- Motor unit recruitment; Biomedical engineering -- Periodicals; Biomedical Engineering -- Periodicals; Physics -- Periodicals; Génie biomédical -- Périodiques; Biomedical engineering; Electronic journals; Periodicals; 610.28
• DOI: 10.1016/j.medengphy.2016.05.012
• Languages: English
• ISSNs: 1350-4533

Abstract

Highlights: This study quantifies the degree of association between mechanomyographic signal and isometric torque of the rectus femoris (RF) muscle during incremental NMES-evoked muscle contractions in persons with spinal cord injury (SCI). Mechanomyography demonstrated a good association with torque production, reliably tracked the motor unit recruitment pattern during NMES-evoked muscle contractions in persons with SCI. The sensitive of the MMG signals to the incremental NMES-evoked muscle contraction torque, measured by a commercial dynamometer (i.e. a "gold standard"), suggests that the signal could be a reliable proxy for these dynamometer measurements. Our findings suggested that the MMG signal could be used to reveal the recovery or deterioration of motor unit output after NMES therapy in denervated muscles, and could also provide diagnostic information, especially for monitoring progress in NMES therapies. Abstract: The interaction between muscle contractions and joint loading produces torques necessary for movements during activities of daily living. However, during neuromuscular electrical stimulation (NMES)-evoked contractions in persons with spinal cord injury (SCI), a simple and reliable proxy of torque at the muscle level has been minimally investigated. Thus, the purpose of this study was to investigate the relationships between muscle mechanomyographic (MMG) characteristics and NMES-evoked isometric quadriceps torques in persons with motor complete SCI. Six SCI participants with lesion levels below C4 [(mean (SD) age, 39.2 (7.9) year; stature, 1.71 (0.05) m; and body mass, 69.3 (12.9) kg)] performed randomly ordered NMES-evoked isometric leg muscle contractions at 30°, 60° and 90° knee flexion angles on an isokinetic dynamometer. MMG signals were detected by an accelerometer-based vibromyographic sensor placed over the belly of rectus femoris muscle. The relationship between MMG root mean square (MMG-RMS) and NMES-evoked torque revealed a very high association ( R 2 = 0.91 at 30°; R 2 = 0.98 at 60°; and R 2 = 0.97 at 90° knee angles; P < 0.001). MMG peak-to-peak (MMG-PTP) and stimulation intensity were less well related ( R 2 = 0.63 at 30°; R 2 = 0.67 at 60°; and R 2 = 0.45 at 90° knee angles), although were still significantly associated ( P ≤ 0.006). Test-retest interclass correlation coefficients (ICC) for the dependent variables ranged from 0.82 to 0.97 for NMES-evoked torque, between 0.65 and 0.79 for MMG-RMS, and from 0.67 to 0.73 for MMG-PTP. Their standard error of measurements (SEM) ranged between 10.1% and 31.6% (of mean values) for torque, MMG-RMS and MMG-PTP. The MMG peak frequency (MMG-PF) of 30 Hz approximated the stimulation frequency, indicating NMES-evoked motor unit firing rate. The results demonstrated knee angle differences in the MMG-RMS versus NMES-isometric torque relationship, but a similar torque related pattern for MMG-PF. These findings suggested that MMG was well associated with torque production, reliably tracking the motor unit recruitment pattern during NMES-evoked muscle contractions. The strong positive relationship between MMG signal and NMES-evoked torque production suggested that the MMG might be deployed as a direct proxy for muscle torque or fatigue measurement during leg exercise and functional movements in the SCI population.