Background: The menstrual cycle (MC) may modulate metabolic, neuromuscular and psychophysiological responses. However, evidence regarding MC phase effects remains inconclusive, particularly in swimming. Aim: To analyze whether MC phases affect training performance and psychophysiological variables (well-being, motivation, recovery, and ratings of perceived exertion [RPE]) in competitive swimmers (Level 3 World Aquatics points). Methods: Twelve adolescent swimmers (14-17 years) with natural MC participated in this longitudinal study (mean body mass: 60.2 ± 5.1 kg; mean height: 164.4 ± 4.0 cm). After familiarization, athletes completed eight weekly control sessions at their usual training facility. Each session included a standardized warm-up and a control set of 9x 100m front crawl at three submaximal intensities based on RPE (4x 100m at RPE 3, 20s rest; 3x 100m at RPE 6, 40s rest; and 2x 100m at RPE 8, 1min rest). Well-being was assessed using a closed-ended questionnaire, motivation through a Likert scale, and recovery through the TQR Scale before each session. RPE was recorded 3 min after the final repetition. MC phases were identified using ovulation tests and menstrual tracking and categorized as menstrual (MP), follicular (FP), ovulatory (OP), luteal (LP), and premenstrual (PMP). Linear mixed models were applied with MC phase as a fixed factor and athlete as a random factor (p < 0.05). Results: No significant differences were observed between MC phases for swimming time, well-being, motivation, recovery, or RPE (all p > 0.05). A trend was observed for time at RPE 8 (p = 0.063), with slower performances during MP, and for RPE (p = 0.141), although differences were not maintained after correction. Conclusions: MC phases did not affect performance or psychophysiological responses, suggesting that submaximal training may not require phase-based adjustments. Future studies should include larger samples, objective hormonal verification, and menstrual symptom assessment to better understand individual responses.
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