Changes in postural activity of the trunk muscles following spinal manipulative therapy

Spinal manipulative therapy (SMT) is common in the management of low back pain (LBP) and has been associated with changes in muscle activity, but evidence is conflicting. This study investigated the effect of SMT on trunk muscle activity in postural tasks in people with and without LBP. In 20 subjects (10 with LBP and 10 controls), EMG recordings were made with fine-wire electrodes inserted into transversus (TrA), obliquus internus (OI), and externus (OE) abdominis. Rectus abdominis (RA) and anterior deltoid EMG was recorded with surface electrodes. Standing subjects rapidly flexed an arm in response to a light, before and after a small amplitude end range rotational lumbar mobilization at L4-5. In controls, there was no change in trunk muscle EMG during the postural perturbation after SMT. In LBP subjects there was an increase in the postural response of OI and an overall increase in OE EMG. There was no change in TrA or RA EMG. These results indicate that SMT changes the functional activity of trunk muscles in people with LBP, but has no effect on control subjects. Importantly, SMT increased the activity of the oblique abdominal muscles with no change in the deep trunk muscle TrA, which is often the target of exercise interventions.