U. Raschke et Db. Chaffin, SUPPORT FOR A LINEAR LENGTH-TENSION RELATION OF THE TORSO EXTENSOR MUSCLES - AN INVESTIGATION OF THE LENGTH AND VELOCITY EMG-FORCE RELATIONSHIPS, Journal of biomechanics, 29(12), 1996, pp. 1597-1604
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.