Objectives: In chronic pain patients, impaired conditioned pain modulation (CPM) and exercise-induced hypoalgesia (EIH) have been reported. No studies have compared CPM and EIH in chronic musculoskeletal pain patients with high pain sensitivity (HPS) and low pain sensitivity (LPS).
Materials and methods: On 2 days, manual pressure pain thresholds (PPTs) were recorded at the legs, arm, and shoulder in 61 chronic pain patients and they performed the cold pressor test, 2 exercise conditions (bicycling and isometric contraction), and a control condition in a randomized and counterbalanced order. PPTs, pain tolerance, pain tolerance limit, and temporal summation of pain were assessed with cuff algometry before and after the tests. On the basis of a median split of the average PPTs for women and men, respectively, low (LPS; N=30) and high (HPS; N=31) pain-sensitivity groups were created.
Results: At baseline, cuff PPT and pain tolerance were decreased and temporal summation of pain was increased in the HPS group (P<0.02). Cuff PPT increased and pain tolerance limit decreased after the cold pressor test and exercises in LPS (P<0.001). Temporal summation of pain was increased after bicycling in HPS (P<0.005). Pain tolerance increased after the cold pressor test and exercise in both groups (P<0.001).
Discussion: CPM and EIH were partly impaired in chronic pain patients with high versus less pain sensitivity, suggesting that the CPM and EIH responses depend on the degree of pain sensitivity. This has clinical implications as clinicians should evaluate pain sensitivity when considering treatment options utilizing the descending modulatory pain control.