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Fear-avoidance behavior has been widely acknowledged among chronic low back pain (LBP) patients. "The central concept of these models is fear of pain, or the more specific fear that physical activities will cause (re)injury. Patients may react to these fears either with 'confrontation' or 'avoidance.'" This current study was designed to see if the fear that patients felt about their back pain translated into a physiological reaction. The authors started with the following hypotheses:
The 31 participants were chosen because they had "minimal organic findings or displayed pain complaints that were disproportionate to the demonstrable organic basis of their pain." The authors distributed questionnaires that measured pain-related fear, negative affect, pain intensity, and perceived tension.
First, the subjects had an EMG of the lower paraspinal muscles while they were watching a video. The video exposure had two segments: the first was a 60-second nature documentary. Before viewing the second, the patients were told they would have to perform what they saw after its completion. Two activities were shown: a person vigorously riding a stationary bike, and exercise measuring extension-flexion. The actor in the video was displaying pain behaviors—groaning, sighing, and gasping. The EMG was in place while the patients were watching, and after the video, the researchers measured tension, intensity, and pain. Immediately after watching these videos of the suffering actors, the participants were led into a room with the exercise equipment.
The authors categorized patients in a "high fearful" and "low fearful" group. The high-fear group had higher scores of tension, and coincidentally, had higher baseline EMG readings in the paraspinal muscles. There were not any significant differences in muscular reactivity between the two groups for any of the muscles. Generally, muscular reactivity decreased during the video exposure. The authors explain that perhaps their reactivity was affected by the experimental setting, feeling safe, and therefore, able to withdraw during the experiment.
The patient's fear of movement was only predictive of reactivity levels of the left erector spinae. But, pain duration turned out to be the predictive model for reactivity of the left paraspinal muscles. The authors write, "This suggests that muscular reactivity associated with pain-related fear occurs early on in the development of chronic pain. An alternative explanation is that patients with longer pain duration are likely to be more disabled, and therefore more easily might have decided to ignore the instructions during the video-exposure."
Negative affect held some predictive power. In symptom-specific reactivity, NA did not moderate, but in both tibialis anterior muscles it did have an effect. Mainly, pain-related fear would predict muscular reactivity in high NA effect patients.
The authors summarize their findings:
"This study is the first to show that the symptom-specific model of psychophysiological reactivity in chronic pain also applies to the domain of pain-related fear. Although of relatively short duration, reactivity of the left paraspinal muscles is also associated with subsequent pain during a physical activity. In addition, we were able to show that in patients who report high NA, pain-related fear also influences muscular reactivity in other muscles as well."Vlaeyen JWS, Seelen HAM, Peters M, et al. Fear of movement/(re)injury and muscular reactivity in chronic low back pain patients: an experimental investigation. Pain 1999;82:297-304.