ABSTRACT
Strategies of lifting, including stance width and techniques have significant effects on spine loading and stability. Previous studies examined the influence of them on muscular and postural response. However it is not clear how the impact of stance width on human musculo-skeletal might vary according to the chosen lifting technique, so we verified this in our study. The present biomechanical study was carried out in 2011. In this study, a whole body musculoskeletal model of lifting was built and validated by experimental data in order to evaluate stance width conditions impact on muscle activation patterns and spine loading during each lifting techniques. Narrow, normal and wide stance conditions were investigated in squat, stoop and semi-squat lifting techniques. The model muscle's activities were validated by comparing with the experimental mus-cle activities which resulted in Pearson's coefficients of greater than 0.8. Results indicate signifi-cant effect of stance width on muscle activities and joint forces of lower extremity which is de-pendent on the used lifting techniques. For instance, the anterior posterior force of knee has been affected by stand width in squat more than stoop. Stance width conditions in each lifting technique exhibit positive and negative aspects and therefore, neither of them can be recommended as the as the perfect technique in terms of biomechanical parameters.
ABSTRACT
Epidemiological studies showed that low back pain after load-carrying and holding is the most common disorder in industrialized countries and cause of dysfunction and economic problems. Variable dynamic loads impose varying moments about the intervertebral joints and cause a threat to balance. The aim of the present study was to compare the postural stability while holding dynamic load among subjects with and without nonspecific low back pain. In this semi-experimental study 24 men [12 healthy and 12 low back pain] participated. Subjects held static and dynamic loads in neutral and flexed trunk position [12 conditions]. Center of pressure [COP] data were used to calculate: displacement, velocity and its standard deviation in Anterior- Posterior [AP] and Medial-Lateral [ML] directions, and path length. The results of repeated measurements and independent T- tests showed that displacement of COP in ML direction in low back pain patients [1.31, 1.22 cm] during holding dynamic loads [10-15 Hz] is more than healthy subjects [1.03, 1.10 cm]. AP displacement, ML velocity and its standard deviation, path length, standard deviation of ML displacement in flexed and AP velocity in standing position during holding dynamic loads are more than static loads. The increased displacement of COP in subjects with low back pain during holding dynamic loads is probably due to higher sensory threshold in this patient. In addition, external perturbations in dynamic loads increase postural sway and may cause spinal injury.