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Effects of physical conditioning on lifting biomechanics.
Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R01-OH-007352, 2005 Dec; :1-87
Although the prophylactic benefits of exercise have been established, the influence of exercise on the biomechanics of lifting remains unknown. The goal of most industrial exercise programs is to optimize the prophylactic effect of exercise in an effort to control of LBDs. Without an understanding of the biomechanical effects of exercise, the choice of exercise protocol design must be based solely on intuition and limited clinical experience. With a knowledge of the mechanisms by which exercise affects biomechanical risk factors, however, exercise can be tailored to maximize the improvement of these risk factors. Therefore, it is necessary to understand how exercise and physical conditioning influences the biomechanics of MMH lifting and associated spinal load and spinal stability. Exercise may influence spinal load and stability through interaction with spinal kinematics and muscle recruitment patterns. The goal of the research was to quantify the effects of exercise on the biomechanical performance, spinal load and stability during MMH lifting tasks. Subjects participated in a 12 week exercise program in one of three protocols including, aerobic exercise, dynamic spine stabilization, or non-exercise control group. Biomechanical measurements of spinal kinematics, torso muscle activity and spinal load during simulated manual materials handling tasks as well as neuromuscular control of stability were recorded before and after the exercise interventions. Manual materials handling (MMH) tasks were simulated by asking the subjects to lift a box loaded with weight-plates equivalent to 10% of their body weight (BW) and in separate conditions loaded with 25% BW. Kinematics of the lifting movement were recorded using electromagnetic motion sensors. Lumbar-pelvic coordination was quantified by the relative timing of lumbar versus pelvic movement and relative motion of the separate lumbar and pelvic angles. Spinal load was estimated from an electromyographic (EMG) assisted model. Input included measured EMG from eight of the primary torso muscles recorded during the dynamic lifting exertions. Output included the spinal compression and co-contraction. Co-contraction was estimated by computing the minimum set of muscle recruitment necessary to achieve equilibrium and comparing it to the muscle forces determined by the EMG-assisted model. Stability was recorded while subjects maintained quiet upright seated posture on a chair without back-rest. Stability was estimated from time-dependent dynamics of the center-of-pressure trajectory representing the control forces necessary to maintain the upright posture of the torso. It is concluded that poor stability is a personal risk factor that interacts with workplace risk factors to contribute to risk of musculoskeletal injury. Prophylactic exercise acts primarily to augment neuromuscular control in individuals with poor stability.
Materials-handling; Manual-materials-handling; Manual-lifting; Biomechanics; Musculoskeletal-system; Spinal-cord; Neuromuscular-function; Neuromotor-function; Injury-prevention
Final Grant Report
NTIS Accession No.
Issue of Publication
Disease and Injury: Musculoskeletal Disorders of the Upper Extremities
National Institute for Occupational Safety and Health
Virginia Polytechnic Institute and State University
Page last reviewed: May 5, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division