The assessment of back muscle capacity using intermittent static contractions. Part II: Validity and reliability of biomechanical correlates of muscle fatigue |
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| Institution: | 1. Occupational Health and Safety Research Institute Robert-Sauvé, Montreal, Quebec, Canada, H3A 3C2;2. School of Rehabilitation, University of Montreal, C.P. 6128, Succursale Centre-Ville, Montreal, Quebec, Canada, H3C 3J7;3. Department of Kinanthropology, University of Sherbrooke, 2500 Boul. Université, Sherbrooke, Quebec, Canada, J1K 2R1;1. Department of Kinesiology, McMaster University, Hamilton, ON, Canada;2. School of Applied Health Sciences, Sheridan College, Brampton, ON, Canada;1. Department of Chemical and Environmental Engineering and Center for Environmental Research and Technology, Bourns College of Engineering, University of California Riverside, 1084 Columbia Ave, Riverside, CA 92507, USA;3. Complex Carbohydrate Research Center, The University of Georgia, 315 Riverbend Rd., Athens, GA 30602, USA;4. Chemical Sciences Division, Oak Ridge National Laboratory, PO Box 2008 MS6341, Oak Ridge, TN 37831, USA;5. Biosciences Division, Oak Ridge National Laboratory, PO Box 2008 MS6341, Oak Ridge, TN 37831, USA;6. BioEnergy Science Center, Oak Ridge National Laboratory, PO Box 2008 MS6341, Oak Ridge, TN 37831, USA;1. Department of General Surgery, The Second People''s Hospital of Guangdong Province, The 3rd Clinical Medicine School, Southern Medical University, Guangzhou, China;2. Department of Gastroenterology, Institute for Gastroenterology and Hepatology, Renmin Hospital of Wuhan University, Wuhan, China;3. Department of Anatomy and Neurobiology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China;4. Department of Vascular Surgery, Southern Hospital, Southern Medical University, Guangzhou, China;5. Organ Transplant Center, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China;1. The Department of Psychology, Nanjing University, Nanjing 210046, People’s Republic of China;2. Department of Psychology, The University of British Columbia, Vancouver, British Columbia, Canada;3. The Brain and Mind Institute, The University of Western Ontario, London, Ontario, Canada;4. The Department of Psychology, The University of Western Ontario, London, Ontario, Canada;5. The Graduate Program in Neuroscience, The University of Western Ontario, London, Ontario, Canada;6. The Department of Physiology and Pharmacology, The University of Western Ontario, London, Ontario, Canada;1. School of Mechanical Engineering, Chongqing University of Technology, Chongqing 400054, China;2. School of Mechanical and Electronical Engineering, Lanzhou University of Technology, Lanzhou 730050, China;3. Engineering Research Centre for Waster Oil Recovery Technology and Equipment, Chongqing 400067, China |
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| Abstract: | IntroductionIn a previous paper, standard surface electromyographic (EMG) indices of muscle fatigue, which are based on the lowering of the median or mean frequencies of the EMG power spectrum in time, were applied during an intermittent absolute endurance test and were evaluated relative to criterion validity and test–retest reliability. The aims of this study were to assess mechanical and alternative EMG correlates of muscle fatigue.MethodsHealthy subjects (44 males and 29 females; age: 20–55 yrs) performed three maximal voluntary contractions (MVC) and an endurance test while standing in a static dynamometer. Surface EMG signals were collected from four pairs of back muscles (multifidus at the L5 level, iliocostalis lumborum at L3, and longissimus at L1 and T10). The test, assessing absolute endurance (90 N m torque), consisted of performing an intermittent extension task to exhaustion. Strength was defined as the peak MVC whereas our endurance criterion was defined as the time to reach exhaustion (Tend) during the endurance test. Mechanical indices quantifying physiological tremor and steadiness were computed from the dynamometer signals (L5/S1 extension moments) along with EMG indices presumably sensitive to variable load sharing between back muscle synergists during the endurance test.ResultsMechanical indices were significantly correlated to Tend (r range: ?0.47 to –0.53) but showed deceiving reliability results. Conversely, the EMG indices were correlated to Tend (r range: ?0.43 to –0.63) with some of them particularly correlated to Strength (r = ? 0.72 to –0.81). In addition, their reliability results were acceptable (intra-class correlation coefficient >0.75; standard error of measurement <10% of the mean) in many cases. Finally, several analyses substantiated their physiological relevance. These findings imply that these new EMG indices could be used to predict absolute endurance as well as strength with the use of a single intermittent and time-limited (5–10 min) absolute endurance test, a practical way to assess the back capacity of chronic low back pain subjects. |
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