Evaluation of postural stability while holding dynamic load in nonspecific low back pain patients

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.