The journal of pain : official journal of the American Pain Society
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Recent developments in cognitive behavioral theory emphasize the role of "psychological flexibility" in adaptive functioning. Psychological flexibility includes processes of acceptance, mindfulness, values, and cognitive defusion. The present study was intended to investigate aspects of psychological flexibility in relation to the functioning of patients with chronic pain. Two hundred sixty patients seeking treatment for chronic pain completed a battery of measures, including an expanded version of an instrument assessing responses to pain that reflect both psychological flexibility and traditionally conceived "pain management strategies" (ie, pacing, relaxation, positive self-statements). Initial psychometric evaluation of the expanded instrument yielded 2 reliable subscales, as hypothesized. Both subscales were correlated with measures of emotional functioning and psychosocial disability, although psychological flexibility achieved larger correlations and was correlated with additional measures of physical functioning, health care use, and work status. Regression analyses indicated that, after pain and patient background variables were statistically controlled, psychological flexibility accounted for significant variance in eight separate measures of functioning while pain management strategies accounted for significant variance in none. These results may call for a shift in our approaches to chronic pain in line with developments taking place in broader areas of behavioral and cognitive therapy. ⋯ This study includes development of an instrument for assessing coping, consisting of traditionally conceived coping strategies and a process that may be unfamiliar to most readers, termed "psychological flexibility." Results demonstrated that this process, a blend of acceptance, values-based action, mindfulness, and cognitive defusion, is significantly related to patient functioning with chronic pain.
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Chronic muscle pain is a major clinical problem that is often associated with fatigue. Conversely, chronic fatigue conditions are commonly associated with muscle pain. We tested the hypothesis that muscle fatigue enhances hyperalgesia associated with injection of acidic saline into muscle. We evaluated mechanical sensitivity of the paw (von Frey) in mice after 2 intramuscular injections of saline (20 microL; pH 4, pH 5, pH 6, pH 7.2) in a fatigue and a control group. To induce fatigue, mice were run for 2 h/day for 2 days prior to the first injection and 2 h/day for 2 days prior to the second injection. Muscle lactate, pCO(2), pO(2), creatinine kinase, phosphate, and histology were examined after the fatigue task and compared to a control group. Grip force was significantly decreased after 2 h of running indicating fatigue. The fatigue task did not induce muscle damage as there was no difference in muscle lactate, pCO(2), pO(2), creatinine kinase, phosphate, or histology. The fatigue task altered the dose-response relationship to intramuscular acidic saline injections. Mechanical hyperalgesia was observed in both fatigue and control groups after intramuscular injection of pH 4.0, but only the fatigue group after injection of pH 5. Neither the fatigue nor the control group developed hyperalgesia in response to intramuscular injection of pH 6 or pH 7.2. In conclusion, fatigue modified the susceptibility of mice to acid injection of pH 5.0 to result in mechanical hyperalgesia after 2 injections of pH 5.0. The fatigue task did not produce measurable changes in the muscle tissue suggesting a central mechanism mediating the enhancement of hyperalgesia. ⋯ These data therefore show that muscle fatigue can enhance the likelihood that one develops pain to a mild insult. Clinically, this could relate to the development of pain from such conditions as repetitive strain injury, and may relate to the interrelationship between chronic pain and fatigue.