This experiment was set up to test the hypothesis that confrontation with feared movements would lead to symptom-specific muscular reactivity in chronic low back pain patients who report high fear of movement/(re)injury. Thirty-one chronic low back pain patients were asked to watch a neutral nature documentary, followed by a fear-eliciting video-presentation, while surface electromyography (EMG) recordings were made from the lower paraspinal and the tibialis anterior muscles. It was further hypothesized that negative affectivity (NA) would moderate the effects of fear on symptom-specific muscular reactivity, as well as the effects of muscular reactivity on pain report. The results were partly as predicted. Unexpectedly, paraspinal EMG-readings decreased during video-exposure but this decrement tended to be less in fearful patients than in the non-fearful patients. Negative affectivity did not moderate this effect, but moderated the effect of pain-related fear on muscular reactivity of lower leg muscles. In addition, NA directly predicted muscular reactivity in the right tibialis anterior muscle. As predicted, there was a significant covariation between left paralumbar muscular activity and pain report. This association was moderated by NA, but in the opposite direction. The findings extend the symptom-specificity model of psychophysiological reactivity, and support the idea that pain-related fear perpetuates pain and pain disability through muscular reactivity.