REF-709 · Giersch, Morrissey, Katch, Colburn, Sims, Stachenfeld & Casa, 2020 · Journal of Science and Medicine in Sport, 2020 Dec;23 · Paper · PubMed

The luteal phase raises core temperature before and throughout exercise in the heat

But sweat rate, skin temperature and exercise heart rate do not differ between cycle phases

B+moderate evidenceMeasured on recreational to highly trained athletesWritten before October 2026, being re-checked

Key Findings

367 articles identified; 9 studies, n=83 participants pooled. Luteal versus follicular phase, aerobic exercise in the heat; Hedges' g.

OutcomeLuteal vs follicularEffect size
Internal temperature (rectal/oesophageal), pre-exercisesignificantly higher in luteal1.231 ± 0.186 (p<0.01) — large
Internal temperature post-exercisesignificantly higher in luteal0.455 ± 0.153 (p<0.01) — moderate
Mean skin temperatureno significant difference—
Sweat rateno significant difference—
Exercise heart rateno significant difference—
The authors' reading: the luteal rise in starting temperature is maintained through and after exercise, not a progressive divergence — the pre-exercise effect (g 1.231) is larger than the post-exercise one (g 0.455).
The measured heat-loss responses did not differ by phase. Sweat rate and mean skin temperature showed no significant difference in the pooled data. (Sweating threshold itself was not a pooled outcome.)

Practical Application

Pooling 9 studies (n=83 women), core temperature was higher in the luteal than the follicular phase before exercise in the heat (g 1.231) and after it (g 0.455), while sweat rate, skin temperature and exercise heart rate did not differ — treat the luteal phase as a smaller thermal margin, not a broken cooling system.
Not from this paper; the base's own practice — act on the margin, not on the physiology: for a hard session in the heat during the luteal phase, buy back the offset — start earlier/cooler, pre-cool, plan mid-session cooling and fluids more aggressively. Do not derate the session on the assumption of impaired thermoregulation.
Do not use "she is in the luteal phase" to explain a poor sweat response or an unusually high heart rate — neither differed by phase here. Not from this paper; the base's own practice: look for dehydration, illness, fuelling or heat-acclimation status instead.
Not from this paper; the base's own practice: pair with heat acclimation (REF-561, REF-002) rather than treating the cycle as a reason to skip heat work — REF-469 reports heat-training adaptations in elite female cyclists.

Limitations

Only 9 studies and 83 participants pooled. The authors themselves call the data limited.
Inference, not from the abstract: phase verification methods likely varied between included studies (see REF-336, REF-337 for why this matters).
Thermoregulatory outcomes only — no pooled performance outcome. A core-temperature difference is not automatically a performance difference; that question is answered by REF-710 and REF-711, which disagree with each other by training status.
Inference, not from the abstract: exercise protocols and environmental conditions differ between studies; the comparison is between natural cycle phases, so it does not describe an athlete on the pill (REF-338).
How this entry was checked and changed
Content correction 2026-09-27
Byline corrected to the paper's authors (Giersch, Morrissey, Katch, Colburn, Sims, Stachenfeld & Casa); the previous list named several people who are not authors.
"Sweating-threshold claim not supported" -> sweating threshold was not a pooled outcome; "at rest" -> pre-exercise; "confidence intervals are wide", "phase verification varied", "mostly non-elite", "contraceptive users excluded" are not in the abstract — removed or labelled as inference.
Lead ▶ now states the pooled finding with n and effect sizes; cooling/fluids/pre-cooling and heat-acclimation advice labelled as the base's own practice.