Objective
The purpose of this study was to evaluate the short- and long-term effects of exercise on neuropathic pain.

Method
Pain responses between rats in the exercise and control groups were compared to evaluate the effects of exercise in neuropathic pain. Materials consisted of 30 male Sprague-Dawley rats (8 weeks old, 180∼200 g), which were divided into an exercise group (n=15) and a control group (n=15). Neuropathic pain was produced by partially injuring the nerve innervating the tail. Running exercise was given on a Rota-rod treadmill exercise machine for 3 weeks (3.1 Km/day, 6 cycle of 9 minutes exercise and 1 minute rest). Behavioral reactions to mechanical allodynia were checked using a von Frey hairs of 2.0 g (19.6 mN) bending force at 10 minutes, 1 hour and 24 hours post-exercise to evaluate the short term effects of exercise. Behavioral reactions to mechanical and thermal allodynia with 4^oC or 40^oC were evaluated 7, 14, 21 and 28 days following exercise.

Result: The exercise group exhibited less tail-flick frequencies to mechanical stimulation from 58.8⁑6.8% to 41.1⁑5.4%, 37.6⁑13.2% at 1 and 24 hours post-exercise compared to the control group, but there was no significant difference between the groups at weeks 1 through 4. In the exercise group, the decrease of tail-flick frequencies were blocked by naloxone (2 mg/kg i.p.). It is suggested that long-lasting muscle exercise (e.g. running) which influences central endorphin mechanisms giving analgetic effects.

Conclusion
The results of this study support the hypothesis that the exercise can reduce neuropathic pain in the acute stage.