REF-710 · Janse de Jonge, Thompson, Chuter, Silk & Thom, 2012 · Medicine & Science in Sports & Exercise, 2012;44 · Paper · PubMed
Menstrual cycle phase cost endurance performance in hot, humid conditions but not in temperate ones
The environment decides whether the cycle shows up at all
Protocol
n = 12 recreationally active women tested per environmental condition (n = 8 analysed per condition). Two cycle phases, verified by estradiol and progesterone: early follicular (days 3-6) and mid-luteal (days 19-25). Two environments: temperate 20°C / 45% RH and hot-humid 32°C / 60% RH.
Test: 60 min of exercise at 60% VO₂max followed by an incremental test to exhaustion (exercise mode not stated in the abstract). Thermoregulatory, cardiorespiratory and perceptual responses measured.
Key Findings
| Condition | Luteal vs follicular |
|---|---|
| Temperate (20°C / 45%) | No performance difference, despite higher resting and submaximal core temperature in the luteal phase |
| Hot-humid (32°C / 60%) | Time to fatigue significantly reduced in the luteal phase, with higher resting and submaximal core temperature, a faster rate of core-temperature rise, higher heart rate, higher minute ventilation and higher perceived exertion |
The luteal core-temperature offset was present in both environments — but only converted into lost performance in hot, humid conditions.
Heat-loss responses did not differ by phase (partitional calorimetry, sweat rate, upper-arm sweat composition), nor did core temperature at exhaustion.
Authors' explanation: exercise plus heat stress on top of the elevated luteal starting temperature produced physiological and perceptual changes and a greater thermosensitivity.
The luteal deficit in the heat came with a coherent strain signature: hotter, climbing faster, higher HR, higher ventilation, feels harder.
Practical Application
In recreationally active women (n = 8 analysed per condition), luteal-phase time to fatigue was significantly shorter in hot, humid conditions (32°C / 60% RH) but not different in temperate ones (20°C / 45% RH), although luteal core temperature was higher in both — in cool or temperate conditions, there is no reason here to reschedule a key session around cycle phase.
In hot and humid conditions, the luteal phase is a real consideration for a recreationally active athlete — expect an earlier fade, a higher heart rate at the same work, and a higher RPE. Not from this paper; the base's own practice: adjust the target, not the athlete's confidence.
Inference, not tested: read the strain signature before blaming the cycle. Hotter + faster temperature rise + higher HR + higher RPE together is the pattern seen here; a single high-HR ride is not.
Inference, not tested here (dry heat was not studied): humidity matters, not air temperature alone — REF-711 found humid heat cost about 7% of work versus dry heat at the same WBGT.
Limitations
Small (12 tested per condition, n = 8 in each analysis) and recreationally active. This is not an elite-athlete finding, and REF-711 found no phase effect on performance in well-trained women (in a different protocol).
Two phases only — the follicular and luteal phases are internally heterogeneous, and the ovulatory window was not tested.
One hot-humid condition (32°C / 60% RH). Where the threshold sits between "temperate, no effect" and "hot-humid, real effect" is not established.
Time to exhaustion after a fixed 60 min preload: a laboratory construct, not a race. Inference: time-to-exhaustion tests are generally more variable than time trials.
Naturally menstruating women only; says nothing about hormonal contraceptive users (REF-338).
How this entry was checked and changed
Content correction 2026-09-27
Type "randomised crossover" -> within-subject phase comparison (the abstract does not state randomisation); Sport "general, cycling" -> "general" and "60 min cycling" -> 60 min of exercise (the abstract does not name the mode).
Added the abstract's null findings on heat-loss responses and core temperature at exhaustion, and the authors' thermosensitivity explanation.
"32°C in dry air" claim (dry heat was not tested here) relabelled as inference pointing to REF-711's dry-vs-humid result; strain-signature, "adjust the target" and TTE-variability statements labelled.
Lead ▶ now states the study's finding with conditions and sample before the advice.