Menstrual Cycle Training Calculator
The luteal phase raises core temperature 0.3 to 0.5°C, drops plasma volume 8%, and blunts carbohydrate oxidation. The follicular phase is the opposite: peak estrogen, lowest core temp, best carb economy. This tool tells you which phase your race falls in and gives you the Cycle-Phase Performance Protocol to adjust your race plan accordingly.
Based on Lebrun (1995), Hausswirth (2011), and Tarnopolsky (2008). Enter your last period date, race date, and cycle length.
EB says
4 phases
cycle-matched plan
Enter your period dates and race date to see your cycle phase and race-day adjustments.
Menstrual cycle training calculator FAQ
Does your period affect running performance?
Yes, but the direction depends on which phase you are in. The follicular phase (roughly days 6 to 13) is associated with peak aerobic performance: estrogen is rising, core temperature is at its seasonal low, and carbohydrate oxidation is efficient. The late luteal phase (roughly the final week before your period) is the most challenging for performance: core temperature rises 0.3 to 0.5 degrees Celsius, plasma volume drops approximately 8%, and carbohydrate oxidation is blunted. Racing in your late luteal phase requires specific adjustments to sodium, hydration, and pacing strategy.
What is the best phase of your cycle to race?
The late follicular phase, just before ovulation (roughly days 10 to 14 of a 28-day cycle), is generally considered the optimal time for endurance racing. Estrogen is at or near its peak, which promotes glycogen storage and improves economy. Core temperature is at its lowest point in the cycle, making heat management easier. VO2max research (Lebrun 1995) shows modest but measurable improvements in aerobic capacity in the follicular versus luteal phase. However, individual variation is high, and many athletes race extremely well in any phase.
How does the luteal phase affect endurance performance?
The luteal phase (roughly days 15 to 28 of a 28-day cycle) brings elevated progesterone, which raises resting core temperature 0.3 to 0.5 degrees Celsius above baseline (Hausswirth 2011). This shrinks the thermal margin before heat stress kicks in, meaning the same external temperature feels harder. Plasma volume drops approximately 8% in the late luteal phase (Beidleman 1997), increasing the cardiovascular strain per unit of effort. Carbohydrate oxidation is measurably blunted (Tarnopolsky 2008), meaning you burn relatively more fat at the same intensity. These three changes compound in hot conditions.
Should I adjust my sodium intake based on my cycle?
Yes, specifically in the late luteal phase. Progesterone has a mild anti-aldosterone effect that promotes sodium excretion, while lower plasma volume concentrates what sodium remains. The Cycle-Phase Performance Protocol recommends increasing sodium targets by approximately 10 to 15% in the late luteal phase compared to your standard race plan. The exact increase depends on your baseline sweat rate and the sodium calculator result for your race conditions.
Does estrogen affect VO2max?
Estrogen has direct effects on aerobic metabolism, though the size of the effect is debated. Lebrun et al. (1995) found statistically significant differences in VO2max across cycle phases in well-trained women. Estrogen promotes glucose uptake in muscle, increases glycogen synthesis, and has vasodilatory effects that improve oxygen delivery. In the late luteal phase, lower estrogen plus high progesterone partially reverses these benefits. In practice, the thermoregulatory and plasma volume effects are often more immediately impactful for race-day performance than the direct VO2max change.
See also: how your menstrual cycle affects training and racing.
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