Mood state across the menstrual cycle during physical work in the heat

BACKGROUND: Increased occupational heat stress is common among laborers and has been projected to increase in the coming decades. At the same time, the number of women in the manual labor workforce is increasing. Performing physical labor in the heat accelerates the onset of fatigue, which is associated with increased mood disturbance and reductions in work capacity. The mid-luteal (ML) phase of the menstrual cycle is characterized by high estrogen and progesterone levels, which have been associated with more negative mood states. In similarity, it is common for women to experience heightened mood disturbances during the low hormone, early-follicular (EF), phase. This study evaluated whether menstrual cycle phase affected mood state during physical work in the heat. We hypothesized that overall mood state would be more positive during the early-follicular (EF) phase compared with the mid-luteal (ML) phase of the menstrual cycle.METHODS: In a randomized crossover design, twelve healthy eumenorrheic females completed two experimental trials corresponding to distinct menstrual cycle phases (EF or ML). Upon arrival to a temperature-controlled laboratory (21.1 ± 0.9 ºC), baseline mood state was assessed using the Profile of Mood States (POMS) questionnaire. Participants then walked on a treadmill for 30 min each hour for four hours in an environmental chamber set to 33.8 ± 0.8 ºC, 54 ± 1% relative humidity while wearing a long sleeve button down shirt and long pants. The POMS was repeated at the end of the four hours with participants still in the chamber and following 20 minutes of recovery in a cooler environment. RESULTS: There was no significant main effect of menstrual cycle phase (p = 0.788) for TMD or any of its variables, though testing stage did show significance (p < 0.001), with an overall increase across all time points. TMD did significantly increase from baseline to work (SE = 2.61, p = 0.009) and decreased from work to recovery (SE = 1.55, p = 0.008) during the EF phase. Fatigue was significantly higher during work compared to baseline during both phases (EF, SE = 1.25, p = 0.038; ML, SE = 0.947, p = 0.010). During the EF phase, vigor was significantly higher during baseline compared to work (SE = 4.22, p = 0.006) and showed a significant increase during recovery compared to work (SE = 0.596, p = 0.042). Similar but nonsignificant patterns were observed in the ML phase (p = ≥ 0.060). CONCLUSION: Although factors of mood disturbance increased during prolonged work in a hot environment, more negative mood states were not observed during the ML phase compared to the EF phase. These findings indicate that menstrual cycle phase does not modify changes in mood state during simulated occupational heat stress in healthy women. Support: R01OH011528 This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.