Effects of mechanical assistance on muscle activity and motor performance during isometric elbow flexion |
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| Institution: | 1. Department of Human Science, Graduate School of Design, Kyushu University, 4-9-1 Shiobaru, Minami-ku, Fukuoka 815-8540, Japan;2. Department of Human Science, Faculty of Design, Kyushu University, 4-9-1 Shiobaru, Minami-ku, Fukuoka 815-8540, Japan;1. Sport Sciences – Performance and Technology, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark;2. Department of Occupational and Environmental Medicine, Danish Ramazzini Centre, Aalborg University Hospital, Aalborg, Denmark;1. Department of Biomechanics in Sports, Technical University Munich, Germany;2. Centre for Sensorimotor Performance, The University of Queensland, Australia;3. Human Movement Science, Bundeswehr University Munich, Germany;1. Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, USA;2. University of Potsdam, Department of Sports and Health Sciences, University Outpatient Clinic, Potsdam, Germany;1. Laboratoire d''Automatique, de Mécanique, et d''Informatique industrielles et Humaines–UMR CNRS 8201, Université Polytechnique Hauts-de-France, Valenciennes, France;2. School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, Canada;3. Centre de Rééducation Fonctionnelle La Rougeville, Saint-Saulve, France;4. Laboratoire de l’Effort et du Mouvement, Haute Ecole Provinciale de Hainaut–Condorcet, Tournai, Belgium |
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| Abstract: | Mechanical assistance on joint movement is generally beneficial; however, its effects on cooperative performance and muscle activity needs to be further explored. This study examined how motor performance and muscle activity are altered when mechanical assistance is provided during isometric force control of ramp-down and hold phases. Thirteen right-handed participants (age: 24.7 ± 1.8 years) performed trajectory tracking tasks. Participants were asked to maintain the reference magnitude of 47 N (REF) during isometric elbow flexion. The force was released to a step-down magnitude of either 75% REF or 50% REF and maintained, with and without mechanical assistance. The ramp-down durations of force release were set to 0.5, 2.5, or 5.0 s. Throughout the experiment, we measured the following: (1) the force output using load cells to compute force variability and overshoot ratio; (2) peak perturbation on the elbow movement using an accelerometer; (3) the surface electromyography (sEMG) from biceps brachii and triceps brachii muscles; and (4) EMG oscillation from the biceps brachii muscle in the bandwidth of 15–45 Hz. Our results indicated that mechanical assistance, which involved greater peak perturbation, demonstrated lower force variability than non-assistance (p < 0.01), while EMG oscillation in the biceps brachii muscle from 15 to 45 Hz was increased (p < 0.05). These findings imply that if assistive force is provided during isometric force control, the central nervous system actively tries to stabilize motor performance by controlling specific motor unit activity in the agonist muscle. |
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| Keywords: | Assistive force Isometric contraction Electromyography Force variability Perturbation |
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