Cyclic load magnitude is a risk factor for a cumulative lower back disorder.
Le-P; Solomonow-M; Zhou-BH; Lu-Y; Patel-V
J Occup Environ Med 2007 Apr; 49(4):375-387
OBJECTIVE: Epidemiological data suggest that high loads lifted by workers engaged in static and cyclic daily activities may be a risk factor for low back disorder. Our previous research provided physiological and biomechanical validation of the epidemiological data for static load conditions. The objective of this report was to provide physiological and biomechanical experimental validation to the epidemiological data in cyclic (repetitive) load conditions. METHODS: Three groups of in vivo feline models were subjected to 3 cyclic load levels in a series of 6 periods of 10 minutes of work spaced by 10 minutes of rest followed by 7 hours of rest. Multifidus electromyography (EMG) and lumbar displacement were statistically analyzed after processing. RESULTS: Delayed muscular hyperexcitability was observed only in moderate (40 N) and high (60 N) loads (P<0.0001) but was absent in low (20 N) loads. The magnitude of the delayed hyperexcitability was found to be higher (P<0.0001) in the high (60 N) loads compared with the moderate (40 N) loads. CONCLUSIONS: Exposure to moderate and high loads in cyclic (repetitive) work results in an acute neuromuscular disorder indicative of soft tissue inflammation that may become chronic with further exposure.
Risk-factors; Back-injuries; Cumulative-trauma-disorders; Muscles; Muscular-disorders; Musculoskeletal-system; Musculoskeletal-system-disorders; Epidemiology; Mathematical-models; Statistical-analysis; Neuromotor-system-disorders; Neuromuscular-system-disorders; In-vivo-studies; Animal-studies
Moshe Solomonow, PhD, MD (Hon), Musculoskeletal Disorders Research Laboratory, University of Colorado Health Sciences Center, 12800 East 19th Avenue, RC-1, North Tower, Mail Stop 8343, Box 6511, Aurora, CO 80045
Journal of Occupational and Environmental Medicine
Louisiana State University, Health Sciences Center, New Orleans, Louisiana