Muscle fatigue does not lead to increased instability of upper extremity repetitive movements |
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| Authors: | Deanna H. Gates Jonathan B. Dingwell |
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| Affiliation: | 1. Department of Biomedical Engineering, University of Texas at Austin, 1 University Station, C0800, Austin, TX 78712, USA;2. Department of Kinesiology & Health Education, University of Texas, Austin, TX 78712, USA;1. Department of Kinesiology and Nutrition, University of Illinois at Chicago, United States;2. Department of Bioengineering, University of Illinois at Chicago, United States;1. Movement Science Laboratory, Scottish Rite for Children, Dallas, TX, USA;2. Biomechanics Laboratory, Department of Kinesiology, Texas Woman’s University, Denton, TX, USA;1. EMPA, Swiss Federal Laboratories for Materials Science and Technology, Mechanical Systems Engineering, Ueberlandstrasse 129, 8400 Duebendorf, Switzerland;2. Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, PA 15261, USA;3. Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15261, USA;4. Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261, USA;1. Rehabilitation Engineering Laboratory, Department of Health Sciences and Technology, ETH Zurich, Switzerland;2. Spinal Cord Injury Center, Balgrist University Hospital, Zurich, Switzerland;3. Occupational Health Management, SBB AG, Swiss Federal Railways, Bern, Switzerland |
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| Abstract: | Muscle fatigue alters neuromuscular responses. This may lead to increased sensitivity to perturbations and possibly to subsequent injury risk. We studied the effects of muscle fatigue on movement stability during a repetitive upper extremity task. Twenty healthy young subjects performed a repetitive work task, similar to sawing, synchronized with a metronome before and after performing each of two fatiguing tasks. The first fatigue task (LIFT) primarily fatigued the shoulder flexor muscles, while the second fatigue task (SAW) fatigued all of the muscles of the arm. Subjects performed each task in random order on two different days at least seven days apart. Instantaneous mean EMG frequencies (IMNF) decreased over both fatiguing tasks indicating that subjects did experience significant muscle fatigue. The slopes of the IMNF over time and the decreases in maximum force measurements demonstrated that the LIFT fatigue task successfully fatigued the shoulder flexors to a greater extent than any other muscle. On average, subjects exhibited more locally stable shoulder movements after the LIFT fatigue task (p=0.035). They also exhibited more orbitally stable shoulder (p=0.021) and elbow (p=0.013) movements after the SAW fatigue task. Subjects also had decreased cocontraction at the wrist post-fatigue for both tasks (p=0.001) and at the shoulder (p<0.001) for the LIFT fatigue task. Therefore, increased dynamic stability of these repeated movements cannot be explained by increased muscle cocontraction. Possible alternative mechanisms are discussed. |
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