Low back joint loading and kinematics during standing
and unsupported sitting
Ergonomics, 44 (3):
280-294 (February 2001)Abstract
The aim was to examine lumbar spine kinematics, spinal
joint loads and trunk muscle activation patterns during
a prolonged (2 h) period of sitting. This information
is necessary to assist the ergonomist in designing work
where posture variation is possible -- particularly
between standing and various styles of sitting. Joint
loads were predicted with a highly detailed anatomical
biomechanical model (that incorporated 104 muscles,
passive ligaments and intervertebral discs), which
utilized biological signals of spine posture and muscle
electromyograms (EMG) from each trial of each subject.
Sitting resulted in significantly higher (p<0.001) low
back compressive loads (mean +/- SD 1698 +/- 467 N)
than those experienced by the lumbar spine during
standing (1076 +/- 243 N). Subjects were equally
divided into adopting one of two sitting strategies: a
single 'static' or a 'dynamic' multiple posture
approach. Within each individual, standing produced a
distinctly different spine posture compared with
sitting, and standing spine postures did not overlap
with flexion postures adopted in sitting when spine
postures were averaged across all eight subjects. A
rest component (as noted in an amplitude probability
distribution function from the EMG) was present for all
muscles monitored in both sitting and standing tasks.
The upper and lower erector spinae muscle groups
exhibited a shifting to higher levels of activation
during sitting. There were no clear muscle activation
level differences in the individuals who adopted
different sitting strategies. Standing appears to be a
good rest from sitting given the reduction in passive
tissue forces. However, the constant loading with
little dynamic movement which characterizes both
standing and sitting would provide little rest/change
for muscular activation levels or low back loading.