Electromyography in Back Research — Assessment of Static and Dynamic Conditions

Abstract

Muscular contraction, as well as relaxation are significantly related to biomechanical strain of the back. Three important problems were selected for our studies, — The electromyo-graphic signs nd, therefore, the detection, of fatigue in lumbar muscles remain an unsolved question (2). Experiment 1 aimed at elucidating electromyographic signs of fatigue of lumbar muscles during sustained isometric contractions of different strength. — According to studies by other authors, the electrical activity of lumbar muscles is low during the initial stage of back lift due to the ‘flexion-relaxation’ (1). However, even dynamic models that have been recently applied for the calculation of compressive forces neglect this fact; the torque counteracting the force moment resulting from body weight and external forces is calculated with the lever arm of back muscles, i.e., 5 cm. Though the combination of a high load and a low muscular activity could mean an extraordinarily high risk during the very first moments of back lift, data are not available on the exact relationship between external forces and the activity of back muscles. The answer to this question requires a correct prediction of the time-course of the force developed by the muscles that is not considered in literature as yet. Experiment 2 aimed at filling these gaps in order to assess better the risk inherent in material handling tasks.

These investigations were part of a vibration research program of the Central Institute for Occupational Medicine of the GDR, Berlin. The authors gratefully acknowledge the assistance and collaboration of M. Godau and R. Vizcaino.