SUPPORT FOR A LINEAR LENGTH-TENSION RELATION OF THE TORSO EXTENSOR MUSCLES - AN INVESTIGATION OF THE LENGTH AND VELOCITY EMG-FORCE RELATIONSHIPS

This study investigated the hypothesis that the length-tension relatio n of the torso erectors would be linear, mirroring the observed linear increase in extension strength capability toward full flexion. The ef fect of torso extension velocity on the tension capability of these mu scles was also investigated for common motion speeds. A myoelectric-ba sed approach was used wherein a dynamic biomechanical model incorporat ing active and passive tissue characteristics provided muscle kinemati c estimates during controlled sagittal plane extension motions. A doub le linear optimization formulation from the literature provided muscle tension estimates. The data of five male subjects supported the hypot hesis of a linear length-tension relation toward full flexion for both the erector spinae and latissimus muscles. Velocity trends agreed wit h that predicted by Hill's exponential relation, although linear trend s were found to fit the data almost as well. The results have implicat ions for muscle tension estimation in biomechanical torso modeling, an d suggest a possible low back pain injury mechanism through tissue str ain while lifting in fully flexed postures. Copyright (C) 1996 Elsevie r Science Ltd.