Delayed Effects Of Mildly Injurious Eccentric Exercise On Thermal Pain Perception

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Reduced sensitivity to painful stimuli can occur immediately after exercise, but little is known about whether eccentric exercise resulting in muscle damage and delayed onset inflammation and pain alters perceptions of concomitant noxious stimuli. PURPOSE: To explore the delayed effects of eccentric exercise on affective and sensory aspects of heat pain sensitivity. METHODS: Six women controls were pre- and post-tested under conditions identical to the exercise group except that no eccentric exercise was performed. Maximal voluntary concentric contraction strength (MVCCS) of the non-dominant elbow flexors was obtained from 10 untrained women who then lowered a dumbbell 18 times with their non-dominant arm. The weight lowering involved three sets of 6 reps at intensities equal to MVCCS. The eccentric exercise caused a minor arm muscle injury that was apparent 24 to 48 hours post-exercise as inferred from statistically significant reductions in both maximal isometric force at 90 degrees (-32.7%) and elbow range of motion (-7.9%) as well as increases in arm volume (2.5%) and arm pain intensity ratings (0 to 100 scale) from 0 to 21 (< 40 = mild) in response to performing a dumbbell arm curl with 50% of MVCCS. Pain ratings, using the intensity and unpleasantness forms of the Descriptor Differential Scale (DDS), were made in response to thermal stimuli applied before eccentric exercise and 24- and 48-hours later. A 30 × 30 mm thermode (TSA-II NeuroSensory Analyzer, Medoc) was used to present heat stimuli to the skin for 2 seconds. Thermal stimuli were applied to a total of 12 unique non-dominant limb sites - six volar forearm (3 medial, 3 lateral) and six posterior lower leg sites. Three randomly ordered temperatures (45, 47, & 49 degrees C) were applied twice to both leg and arm sites. RESULTS: Treatment (Eccentric Exercise versus Control) × Time (Pre versus Post [mean of 24- & 48-hour data]) ANOVA showed a significant interaction for arm pain intensity ratings at 49 degrees C (F1,14=5.613, p=.033). One-to-two days after exercise, pain intensity was reduced by 11% and differed from the controls at the post-test by 0.47 standard deviations. CONCLUSION: One to two days after injurious eccentric exercise the perceived intensity of moderately painful heat stimuli applied to the skin in the same dermatome of the exercised muscle is reduced.