The Influence of the Menstrual Cycle on Electrical Thresholds for Sensory and Pain Perception: Implications for Exercise and Rehabilitation in Women With and Without Primary Dysmenorrhea—A Pilot Study

<b>Background</b>: Hormonal fluctuations during the menstrual cycle (MC) influence pain perception, potentially affecting exercise performance and rehabilitation in women. This effect may be more pronounced in individuals with primary dysmenorrhea (PD), requiring tailored physiotherapeutic and exercise interventions. <b>Objective</b>: To analyze the influence of MC phases on sensory electrical threshold (SET) and pain electrical threshold (PET) in eumenorrheic women with and without PD, considering the potential implications for physical activity and rehabilitation. <b>Methods</b>: An observational longitudinal study was conducted with 34 physically active women, divided into a control group (CG) and a PD group. SET and PET were measured using transcutaneous electrical nerve stimulation (TENS) at the forearm (peripheral site) and lower abdomen (pain-referred site) across five MC phases. Pain intensity was assessed using a Visual Analog Scale (VAS). <b>Results</b>: SET and PET were significantly lower in the premenstrual phase (<i>p</i> < 0.001), suggesting increased pain sensitivity. VAS scores were higher in the PD group during all phases, except for the follicular phase (<i>p</i> < 0.033), with the highest pain levels recorded in the menstrual and premenstrual phases. While no significant differences in SET and PET were found between groups across most phases, the PD group exhibited a significantly higher SET in the forearm during the premenstrual phase (<i>p</i> = 0.005), potentially indicating altered central pain modulation. <b>Conclusions</b>: MC-related hormonal fluctuations affect pain sensitivity, particularly in women with PD. These findings underscore the need for phase-specific exercise adaptations and rehabilitation strategies to improve performance, pain management, and recovery in physically active women.