A biomechanical analysis of pelvic tilt control and trunk muscle activity during isometric and dynamic lifting

The purpose of this study was to perform a quantitative biomechanical analysis of the lumbar spine as subjects performed isometric and dynamic lifting tasks to determine the degree to which voluntary muscle contraction can control the attitude of the pelvis during these activities. Twenty-two healthy subjects (x̄ = 22.7 years; 69.5kg; 173.7 cm) volunteered from the University of Tennessee at Knoxville, Community.Pelvic tilt, lumbar lordosis, hip, knee and ankle angles were measured using photography as subjects performed 1) isometric and isokinetic lifts (30 & 60 cm/s) on a Cybex Liftask dynamometer and 2) functional box lifts. Electromyography (EMG) was used to monitor activity from the internal oblique (10), external oblique (EG), erector spinae (ES) and gluteus maximus (GM) muscles as the subjects performed the lifts.Force data were quantified for the isometric and isokinetic lifting tasks. In addition,video and EMG data were also collected during functional box lifts.Each subject served as his or her own control. Upon completion of the four lifting conditions, subjects underwent a training session on the neutral spine posture and muscular co-contraction technique; all lifting conditions were then repeated using the neutral spine posture.The results of the repeated measures ANOVA demonstrated no significant pre to post EMG changes; however there were significant differences in activity among the four muscles, with the ES exhibiting the highest activity for all conditions. The force values were significantly reduced in the neutral spine posture conditions, which may be partially explained by the change in the posture itself or due to changing the complexity of the lifting task by incorporating the neutral spine technique. Kinematic results demonstrated that during standing isometric and dynamic lifting (isokinetic and box),utilization of the neutral spine posture via muscular co-contraction limited the range of pelvic and lumbar spine movement, as compared to lifting without a neutral spine position. These results also demonstrated that same day instruction of the neutral spine technique was effective in producing lumbar spine stabilization.The significance of these findings has implications in injury prevention and rehabilitation in occupational, athletic and recreational settings. Utilization of the neutral spine technique during these activities may serve to minimize the forces on the low back, thereby reducing injury incidence and facilitating pain management and rehabilitation.