Biomed. Eng.-Biomed. Tech. 2018; aop Nurul Salwani Mohamad Saadon, Nur Azah Hamzaid*, Nazirah Hasnan, Muhammad Afiq Dzulkifli and Glen M. Davis Electrically evoked wrist extensor muscle fatigue throughout repetitive motion as measured by mechanomyography and near-infrared spectroscopy https://doi.org/10.1515/bmt-2018-0058 Received December 5, 2017; accepted August 6, 2018 Abstract: Repetitive electrically-evoked muscle con- traction leads to accelerated muscle fatigue. This study assessed electrically-evoked fatiguing muscle with changes to mechanomyography root mean square per- centage (%RMS-MMG) and tissue saturation index (%TSI) in extensor carpi radialis. Forty healthy volunteers (n = 40) performed repetitive electrical-evoked wrist extension to fatigue and results were analyzed pre- and post-fatigue, i.e. 50% power output (%PO) drop. Responses of %PO, %TSI and %RMS-MMG were correlated while the relation- ships between %RMS-MMG and %TSI were investigated using linear regression. The %TSI for both groups were negatively correlated with declining %PO as the ability of the muscle to take up oxygen became limited due to fatigued muscle. The %RMS-MMG behaved in two differ- ent patterns post-fatigue against declining %PO whereby; (i) group A showed positive correlation (%RMS-MMG decreased) throughout the session and (ii) group B dem- onstrated negative correlation (%RMS-MMG increased) with declining %PO until the end of the session. Regres- sion analysis showed %TSI was inversely proportional to %RMS-MMG during post-fatigue in group A. Small gradi- ents in both groups suggested that %TSI was not sensitive to the changes in %RMS-MMG and they were mutually exclusive. Most correlation and regression changed sig- nificantly post-fatigue indicating that after fatigue, the condition of muscle had changed mechanically and physiologically. Keywords: fatigue; functional electrical stimulation; muscle oxygenation; muscle strength; rehabilitation; upper limb. List of non-standard abbreviations: ATT, adipose tissue thickness; ECR, extensor carpi radialis; EMG, electromyo- graphy; FES, functional electrical stimulation; HHb, deox- yhemoglobin; MMG, mechanomyography; NIRS, near infrared spectroscopy; O 2 Hb, oxyhemoglobin; PO, power output; RMS, root mean square; StO 2 , oxygen saturation; TSI, tissue saturation index; VMG, vibromyography. Introduction Neuromuscular electrical stimulation therapies including functional electrical stimulation (FES) training, are often prescribed to individuals with paralysis/paresis arising from central nervous system injury. Colson et al. have con- cluded that FES might be more efficient than voluntary iso- metric training in order to improve the strength of muscle [1]. However, muscle contractions elicited by FES are more susceptible to rapid-onset fatigue than voluntary con- tractions due to their synchronous pattern of motor unit recruitment and the preferential stimulation of large dia- meter neurons innervating fast-fatiguing muscle fibers [2]. Muscle fatigue has been understood to be a decline in muscle ability to generate force or power output (PO) [3] as well as a reduction in movement speed [4] of volun- tary contractions [5]. Packman-Braun proposed a fatigue criterion as a 50% decrease from the muscle’s initial force output [6]. Researchers have investigated muscle fatigue under various conditions involving numerous muscles to understand the characteristics of different muscles since they may be relatively dissimilar among individuals [7]. Electromyography (EMG) is one approach to under- stand muscle activity and its pathological changes for both diagnostic and therapeutic purposes. It is also often *Corresponding author: Nur Azah Hamzaid, Department of Biomedical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia, Phone: +603-79674487, Fax: +603-79674579, E-mail: azah.hamzaid@um.edu.my Nurul Salwani Mohamad Saadon and Muhammad Afiq Dzulkifli: Department of Biomedical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur, Malaysia Nazirah Hasnan: Department of Rehabilitation Medicine, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia Glen M. Davis: Clinical Exercise and Rehabilitation Unit, Discipline of Exercise and Sports Sciences, Faculty of Health Sciences, University of Sydney, Lidcombe, Australia Authenticated | azah.hamzaid@um.edu.my author's copy Download Date | 9/21/18 3:37 AM