Dynamic adjustments of walking behavior dependent on noxious input in experimental low back pain.

The aim of this study was to explore whether accelerations of the lower back during walking are temporarily attenuated by experimentally-induced low back pain, as compared with normal walking. Transient low back pain was induced by injection of 1 ml 6% hypertonic saline in the longissimus dorsi muscle in 20 healthy subjects. Acceleration was measured during walking at self-selected speeds before and repeatedly after the injection by a portable, triaxial accelerometer positioned over the L3 region. Data were subsequently adjusted for differences in walking speeds between trials and subjects. Pain was reported on a 0-10 point scale during walking until pain was no longer present. Lumbar acceleration sample mean was attenuated for the anteroposterior (P=0.002) and mediolateral (P=0.002) sensing axes as well as for the vector sum (P=0.005) at maximal pain compared to pretest values. The vertical axis showed no significant changes. Values returned to pretest level when pain was no longer present. Regardless of the initial increase and subsequent decrease in pain after injection, there was a linear relationship between pain and acceleration in 15 of the 20 subjects (0.89>/=R(2)>/=0.36, P</=0.002), suggesting a continuous dynamic adjustment of motor behavior dependent on the noxious input. It appears that this new method is suitable for detection of continuous subconscious changes of body accelerations during walking in relation to pain.