Pocket-size, portable surface EMG device in the differentiation of low back pain patients.

The relevance of surface EMG of the paraspinal muscles measured by a portable, pocket-size device with a special amplifier was evaluated in different low back pain groups. Patients with only local low back pain had significantly higher EMG activities than those with unilateral radiating pain without verified disc herniation, those with verified disc herniation, and controls, but there were no differences between the latter three groups. Pain clearly modified paravertebral muscle activity, as the patients experiencing pain during the recording showed significantly higher EMG activities than those with no pain. It is concluded that surface EMG is a valid tool for indirectly assessing pain in low back pain patients but not for classification into different diagnostic groups.