Resistance Training Before Hyperalgesia Induction Promotes Analgesic Effects Through Central and Peripheral Biomarker Modulation in an Experimental Fibromyalgia-like Model.

BACKGROUND: Fibromyalgia is a chronic syndrome characterized by widespread pain and complex pathophysiology, requiring new therapeutic approaches. This study aims to investigate the effects of resistance training (RT) before hyperalgesia induction on pain sensitivity, IL-6 and IL-10 expression in skeletal muscle, and thalamic serotonin levels in a fibromyalgia (FM)-like rat model. METHODS: Wistar female rats aged 12 months were divided into four groups: untrained neutral saline (UNS), untrained acid saline (UAS), RT neutral saline (RTN), and RT acid saline (RTA). Both the RTN and RTA groups were subjected to an RT protocol comprising vertical ladder climbing three times a week throughout 14 weeks. The UAS and RTA groups received 100 µL of neutral, sterile saline (pH 4.0) in the left gastrocnemius muscle, while the UNS and RTN groups received 100 µL of neutral saline (pH 7.4). Mechanical hyperalgesia was assessed using Von Frey's electronic esthesiometer. Expression of interleukins 6 (IL-6) and 10 (IL-10) was analyzed in skeletal muscle, and serotonin expression was quantified in the thalamus. RESULTS: After hyperalgesia induction, the RT groups demonstrated higher paw withdrawal thresholds than the UAS group (p < 0.05). Both IL-6 and IL-10 expression was lower in the RTA group compared to the UAS group (p < 0.05). Thalamic serotonin expression was higher (p < 0.05) in the RTA group compared to the UAS group. CONCLUSION: Previous RT was able to prevent mechanical hyperalgesia experienced by rats after its induction by acid saline by preventing the increase in the IL-6 and IL-10 levels in skeletal muscle and preventing the decrease in thalamic serotonin expression.