~ 135 ~ International Journal of Physical Education, Sports and Health 2017; 4(1): 135-140 P-ISSN: 2394-1685 E-ISSN: 2394-1693 Impact Factor (ISRA): 5.38 IJPESH 2017; 4(1): 135-140 © 2017 IJPESH www.kheljournal.com Received: 26-11-2016 Accepted: 27-12-2016 Ethan C Hill Department of Nutrition and Health Sciences, Human Performance Laboratory University of Nebraska-Lincoln Lincoln, NE 68505, USA Terry J Housh Department of Nutrition and Health Sciences, Human Performance Laboratory University of Nebraska-Lincoln Lincoln, NE 68505, USA Clayton L Camic Department of Exercise & Sport Science, University of Wisconsin- La Crosse La Crosse, WI 54601 Cory M Smith Department of Nutrition and Health Sciences, Human Performance Laboratory University of Nebraska-Lincoln Lincoln, NE 68505, USA Joshua L Keller Department of Nutrition and Health Sciences, Human Performance Laboratory University of Nebraska-Lincoln Lincoln, NE 68505, USA Richard J Schmidt Department of Nutrition and Health Sciences, Human Performance Laboratory University of Nebraska-Lincoln Lincoln, NE 68505, USA Glen O Johnson Department of Nutrition and Health Sciences, Human Performance Laboratory University of Nebraska-Lincoln Lincoln, NE 68505, USA Correspondence Ethan C Hill Department of Nutrition and Health Sciences, Human Performance Laboratory University of Nebraska-Lincoln Lincoln, NE 68505, USA Electromechanical efficiency tracks eccentric torque production Ethan C Hill, Terry J Housh, Clayton L Camic, Cory M Smith, Joshua L Keller, Richard J Schmidt and Glen O Johnson Abstract It has been suggested that electromechanical efficiency may be useful for detecting changes in muscle function as it provides a direct measurement from the muscle being investigated. No previous investigations, however, have examined electromechanical efficiency during fatiguing eccentric exercise. Thus, the purpose of the present study was to examine electromechanical efficiency at velocities of 60°·s - 1 and 180°·s -1 during fatiguing, maximal eccentric muscle actions. Ten men performed 30 maximal eccentric muscle actions of the leg extensors at 60°·s -1 and 180°·s -1 . Polynomial regression analyses were used to examine the composite patterns of responses for eccentric torque, electromyographic amplitude, mechanomyo graphic amplitude, and electromechanical efficiency across the fatiguing protocols. There were no significant relationships for torque or electromechanical efficiency across either of the fatiguing protocols. During the 60°·s -1 protocol, however, electromyographic amplitude decreased linearly (r = 0.579) and mechanomyo graphic amplitude decreased quadratically (R = 0.438), while there were no changes during the 180°·s -1 protocol. These findings indicated that electromechanical efficiency can be applied to fatiguing eccentric exercise and tracks eccentric torque production despite divergent electromyographic and mechanomyo graphic amplitude responses. Keywords: Muscle lengthening, electromyography, muscle damage, motor control, isokinetic 1. Introduction Surface electromyography (EMG) records and quantifies the action potentials that activate skeletal muscle fibers [2] . The amplitude of the EMG signal is generated by the summation of the action potential trains from the active motor units and is influenced by the number of active motor units, their firing rates, and synchronization [2, 3] . The power spectrum of the EMG signal is, in part, determined by average muscle fiber action potential conduction velocity [4] and the shape of the action potential waveforms [5] . Mechanomyography (MMG) is a non- invasive technique that has been described as the mechanical counterpart of motor unit activity as measured by EMG [6] . It has been suggested that the amplitude of the MMG signal is influenced by motor unit recruitment and the frequency content of the MMG signal is qualitatively related to motor unit firing rate [7, 9] . The simultaneous measurements of EMG and MMG have been used to examine various aspects of muscle function including electromechanical and phonomechanical delay [10] , muscle fiber type distribution patterns [11] , muscle atrophy [12] , and excitation-contraction coupling associated with muscle fatigue [13] . EMG and MMG measurements have also been used in pediatric, adult, and geriatric populations to examine neuromuscular disorders such as myotonic dystrophy [14, 15] , mandibular disorders [16] , low back pain [17] , cerebral palsy [18] , to control prostheses [1] , and to examine patellofemoral pain [19] . For example, electrical efficiency, originally described by Lenman [20] and deVries [21] , is an indirect assessment of muscle function that is performed by plotting the integrated electrical activity (EMG) as a function of force production. With regard to clinical and athletic populations, it has been reported that electrical efficiency is lower in individuals with muscular disorders (i.e. muscular dystrophy) relative to asymptomatic individuals [20] , and electrical efficiency decreases with the development of muscle fatigue [22] , but electrical efficiency increases in response to exercise training (improved muscle efficiency) [20, 21] . Barry et al, [1] suggested, however, that