Use of lumbar trunk muscles in isometric performance of mechanically complex standing tasks.

Ten subjects performed 25 tasks isometrically while standing. Those tasks imposed substantial extension, lateral bending, and twisting moments on the lumbar spine. Mechanically complex trunk muscle actions were called for to resist those moments. Biomechanical model analyses were used to predict the trunk muscle contraction forces needed to perform those tasks, and surface myoelectric activities were measured to validate those predictions. Predictions and measurements were linearly well correlated.