The effect of six weeks of HIIT training on pain tolerance threshold in rats with Parkinson's disease (Running title: HIIT training and pain tolerance threshold)

Background and purpose: One of the common and liberating side effects of Parkinson's disease (PD) is pain and its related mechanisms. In this category of patients, the effect of high intensity interval training (HIIT) on the amount of pain and the related mechanisms have not been determined correctly. Therefore, this study was conducted with the aim of investigating the effect of 6 weeks HIT swimming training on the pain tolerance threshold and MOR1 gene expression in rats with PD. Materials and methods: In this experimental study, 21 male Wistar rats aged 8-10 weeks with an average weight of 200 ± 10.2 grams were randomly divided into three groups: healthy control group, PD group and training group. PD was induced by injecting 1 mg/kg body weight of reserpine for 5 days. The training group performed 20 30-second swimming bouts with 30-second rest between each bout for six weeks. The results were analyzed using one-way analysis of variance and Tukey's post hoc test at a significance level of P<0.05 and SPSS-22 software. Results: The results showed that the pain tolerance threshold (P=0.001) and MOR1 gene expression (P=0.003) in the PD group were significantly lower than healthy control group and training group. No significant differences were observed in the pain tolerance threshold (P=0.49) and MOR1 gene expression (P=0.16) between healthy control group and training group. Conclusion: According to the obtained results, HIT swimming training are recommended to reduce the pain of PD patients.