Why Midlife Women Feel Strong One Week and Terrible the Next (It's Not Fitness)

Stacy Sims contrasts this approach with the older model of fixed follicular (hard) and luteal (steady) training, which assumed a predictable, ovulatory 28-day cycle. Over the past five to six years, research shows that inter- and intra-individual variability is so high that calendar-based prescriptions often fail. Many women have anovulatory cycles without knowing it, making the luteal phase assumption invalid. By tracking one's own symptoms, a woman can discover that, for instance, day 21 is always a low-energy day, while day 1 might be her strongest. This insight removes the mystery and self-blame ('What's wrong with me?') and instead provides permission to adjust. Sims reinforces that increasing load on good days creates a greater training stress, which the body then overcomes, accelerating fitness. This is the bedrock of exercise physiology: stress + recovery = adaptation. Ignoring your body's signals and trying to grind through every workout can stall progress.

Sims emphasizes that the bleed phase has been largely absent from public conversations about the menstrual cycle. While the menstrual cycle is discussed in terms of fertility and hormonal shifts, the actual bleeding and associated pain are rarely dissected as normal versus abnormal. She encourages parents and educators to talk openly with girls about what's typical, so they don't grow up thinking that debilitating pain is just part of being a woman. Pain on ovulation, too, is a legitimate phenomenon that can be addressed but is seldom mentioned. By normalizing these discussions, the goal is to catch conditions like endometriosis, fibroids, or hormonal imbalances earlier, and to empower women to seek solutions instead of accepting diminished quality of life.

Sims explains that the older model, based on a limited molecular understanding, gave way to data revealing profound inter- and intra-individual variability. Women might feel flat on a day when the textbook says they should feel strong, leading to frustration and self-blame. By tracking symptoms over several cycles, a woman learns her own 'good' and 'bad' days. This knowledge reduces negative self-talk ('I'm not fit enough') and allows her to adjust training intensity accordingly. For example, Sims personally wanted her period on race day because she felt best the day before and day one, yet on day 21 she avoids hard sessions. The key insight: fitness accelerates when you push hard on days you feel great, because your body can handle greater training stress and then adapt. Trying to grind through low-energy days can blunt adaptation and erode confidence. The prevalence of anovulatory cycles (a bleed without ovulation) makes it even harder to rely on a predictable luteal phase, reinforcing the need for individualized tracking.

Sims stresses that because of stress, intense training, or other lifestyle factors, anovulatory cycles are on the rise. The resulting bleed may be heavier or shorter, but without tracking basal body temperature or symptoms, a woman cannot know whether she ovulated. This means that exercising according to a predicted ‘luteal phase’ could be completely misaligned with her actual hormonal state. She advocates looking for personal patterns rather than relying on a calendar, because the only reliable indicator is how you feel day to day.

Sims emphasizes that if a period causes someone to miss school, work, or training, it is not something to dread or endure—it's treatable. She frequently tells young girls to talk to a parent or doctor because there are interventions that can help. The conversation matters because acknowledging what is within the range of normal (e.g., some discomfort) versus what is outside it empowers women to advocate for their health. She also notes that even pain upon ovulation, seldom discussed, is a real phenomenon that can be addressed. By broadening the dialogue, more women will realize their experiences are not just 'how it is.'