INTRODUCTION: Menstrual cycle (MC) and period length exhibit significant variation among naturally menstruating women. Misconceptions are prevalent due to the assumption that the typical MC is 28 days without considering factors that may impact length. Many women experience physical and psychological MC related symptoms, but their impact is unknown. This analysis aimed to characterize MC length, period length, and symptom prevalence in a population of recreationally active to active naturally menstruating women. Additionally, the impact of body composition on MC characteristics were explored. METHODS: Data were analyzed for 45 recreationally active and 45 active women (mean±SD; age: 22.6±6.3 yrs, BMI: 23.8±4.0 kg/m2, weight: 64.8±7.2 kg). Average period length (days), age of menarche (yrs), and symptoms were collected using a self-reported health history questionnaire. Daily basal body temperature and symptom tracking determined MC length (days). Body composition (percent fat, lean mass, and bone mineral density) was measured using dual-energy x-ray absorptiometry (DXA). Descriptive statistics were used to characterize period and MC length. One-way ANOVAs were used to explore between groups differences. Pearson correlations evaluated period length and body composition. RESULTS: The average period length for recreationally active women was (mean ± SD) [min-max] 4.7 ± 1.2 [3-8] days with an MC length of 28.0 ± 4.7 [18-40] days. For active women, average period length was reported as 4.8 ± 1.3 [3-8] days, with no statistical differences observed between groups (MD: -0.06 ± 0.24 days; p>0.05). There were no correlations between period length, body composition (p=0.525-0.951), or MC symptoms (p>0.05). 95% of active women reported MC related symptoms. 62% reported > 3 symptoms with the most common being cramps (71%), hunger (62%), and bloating (40%). CONCLUSION: Individual variability exists among MC and period length but does not appear to be modulated by activity, with an average bleed time of 4.7 days, and MC length of 28 days, with some lasting 40 days. Negative symptoms associated with the MC are highly prevalent but are not modulated by body composition or period characteristics. Exercise readiness and performance may be influenced by the duration and timing of their MC, especially when experiencing a multitude of MC related symptoms.

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