Effects of experimentally induced lumbar nociception on trunk motor control in the rat during locomotion.

Nociception resulting in pain perception might be one of the factors contributing to the motor control changes in people with low-back pain. However, limited evidence exists regarding the effects of acute pain on trunk motor control during locomotion. This study aimed to evaluate the effects of hypertonic saline induced nociception on trunk movement and back muscle activity during locomotion in a rat model. Spine and pelvis kinematics, EMG signals from bilateral multifidus (MF) and medial longissimus (ML) muscles of the rats were collected during treadmill locomotion before and after hypertonic saline (5.8%) injection into the MF. We found that both the locomotion and EMG patterns remained unchanged after hypertonic saline injection. No significant changes were found in stride duration, pelvic, lumbar and spine angle changes, variability, or movement asymmetry. The overall EMG activation patterns and intermuscular coordination remained unchanged after hypertonic saline injection and there was synchronized activation of bilateral MF muscles with two peaks per stride cycle, and alternating activation of left and right ML. The only significant effects of hypertonic saline injection were the decrease in the normalized peak amplitude of the left MF and EMG variability in right ML, no effects were detected in other EMG outcomes or muscles. These results suggest that the changes in EMG activity reflect localized neuromuscular response to nociception rather than broader alterations in control of locomotion.