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Relaxation phenomenon in lumbar trunk muscles during lateral bending.
Raftopoulos DD; Rafko MC; Green M; Schultz AB
Clin Biomech 1988 Aug; 3(3):166-172
Myoelectric activities in lumbar muscles and biomechanical analyses were carried out to determine if a flexion/relaxation phenomenon arose in lateral trunk bending. Nine male volunteers, aged 21 to 25, performed five tasks involving different degrees of lateral bending in a testing apparatus. Configurations and myoelectric activities were measured during performance of each task. Bilateral posterior and anterior myoelectric activity was obtained at the L3 level. A 22 muscle biomechanical model was used to compute contraction forces in lumbar trunk muscles and compression and shear load acting on the spine for each task and each subject. Correlations were analyzed for mean predicted muscle contraction tissue tension forces and mean measured amplitudes of myoelectric signals. No relaxation phenomenon was noted for left or right oblique abdominal muscles, either with no load or with a 5 kilogram load held in the hand on the side to which bending occurred. Although erector spinae muscles showed no relaxation during lateral bending from upright to maximum bend, they did exhibit relaxation during straightening from maximum bend to upright. A high degree of linear correlation was found for predicted contraction forces versus measured myoelectric activities, with correlation coefficients ranging from 0.72 to 0.87 on both sides of the body. Relaxation effects were no longer noted on reaching 30 to 40 degrees of lateral bend during return from the maximum position. When an external load was used in bent postures or quiet standing, trunk muscle myoelectric activities increased. The authors conclude that passive mechanisms for maintenance of equilibrium are present when standing in a maximum laterally bent position, but the effects are not strong.
NIOSH-Publication; NIOSH-Grant; Musculoskeletal-system-disorders; Biomechanics; Muscle-function; Analytical-models; Humans; Electrophysiological-measurements; Muscle-tension; Body-mechanics; Posture
Mechanical Engineering University of Michigan Dept of Mech. Engr Ann Arbor, Mich 48109
Issue of Publication
University of Michigan at Ann Arbor, Ann Arbor, Michigan
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division