U. Raschke et Db. Chaffin, TRUNK AND HIP MUSCLE RECRUITMENT IN RESPONSE TO EXTERNAL ANTERIOR LUMBOSACRAL SHEAR AND MOMENT LOADS, Clinical biomechanics, 11(3), 1996, pp. 145-152
The response of select lumbar torso and pelvic muscles to loads applie
d at the lumbar spine and across the pelvis was investigated to help i
dentify the sources of antagonistic lower torso muscle recruitment. Fi
ve subjects in the neutral upright posture were loaded with L(4-5) mom
ent and anterior shear forces under constrained and free pelvic rotati
on conditions. The activity states of the erector spinae, latissimus d
orsi, external oblique, rectus abdominis, gluteus maximus, and rectus
femoris muscles were monitored using surface electromyography. Regress
ion analysis was used to test if (1) lumbar shear loads influence the
activity of the torso muscles, and (2) moments about the pelvis signif
icantly influence the torso muscle activities. The pelvic muscles (glu
teus maximus and rectus femoris) were monitored for their role in stab
ilizing pelvic rotation. The statistical analysis did not support the
hypothesis that torso muscles are recruited in response to shear loadi
ng. Also, the data did not provide conclusive evidence that moments ab
out the pelvis relative to the lumbar spine significantly influence to
rso muscle recruitment. For the subjects that exhibited elevated antag
onistic muscle activity, no explanation of this recruitment strategy c
ould be statistically related to lumbar shear or pelvic moments. Relev
ance-Omission of pelvic moments in biomechanical modelling of the lumb
ar torso does not seem to be introducing significant error in the pred
iction of torso muscle activity. The results of this study indicate th
at the source of lumbar torso muscle antagonistic activity under sagit
tal plane flexion loading seems to be a result of yet unidentified fac
tors.