The Effects Of The Menstrual Cycle On Lactate Threshold And Psychological Markers In Females

Intro: Estrogen and progesterone regulate the menstrual cycle (MC) and influence metabolism and psychological factors during exercise in females. Purpose: This study examined MC effects on lactate threshold (LT) and psychological markers in females. Methods: 8 females (20.9 ± 3.9 yrs) and 8 males (24.8 ± 5.5 yrs) participated in the study. Cycle ergometer LT tests were conducted during three MC phases: early follicular (EF; days 1-3), ovulatory (O; within 24 hrs of positive urinary ovulation test), and mid-luteal (ML; 7-10 days post-O). Males were assigned at intervals matching a 28-day cycle to serve as controls. Blood lactate samples were collected during the final minute of each 3-minute stage alongside ratings of perceived exertion (RPE). The first stage was set at 1 W/kg of body weight, and resistance was increased by 0.5 W/kg thereafter. LT was determined using fixed blood lactate concentrations of 2.0 and 4.0 mmol/L. Profile of Mood States (POMS) and pain (VAS) ratings were recorded prior to each visit. Results: Power at LT did not significantly differ between groups or across MC phases (p > 0.05). End-test power was significantly higher for males (p = 0.024, EF: 232.13 ± 82.97 W vs 158.50 ± 31.22 W, O: 227.63 ± 89.19 W vs 149.13 ± 12.93 W, ML: 233.25 ± 84.44 W vs 149.06 ± 24.51 W). End-test RPE was not significantly different between groups or across phases, but a large effect size was observed during EF in females (p > 0.05, ηp2 = 0.188, EF: 8.50 ± 1.69 vs 9.00 ± 1.20). Notably, female fatigue levels were significantly higher than those of males across all phases (p = 0.025, EF: 3.38 ± 4.10 vs 1.25 ± 1.04, O: 3.13 ± 2.42 vs 1.00 ± 1.07, ML: 4.25 ± 4.10 vs 1.13 ± 0.64). Pain was significantly higher in females during EF compared to males and other MC phases (p = 0.031, EF: 15.79 ± 17.40 vs 0.92 ± 2.21, O: 1.59 ± 2.11 vs 0.26 ± 0.74, ML: 2.80 ± 4.52 vs 0.28 ± 0.51). Conclusions: The MC does not significantly impact power at LT in untrained females and elevated pain and fatigue levels do not seem to impair exercise performance. Although there were no statistically significant differences in RPE across phases, effect size was large. Participants generally rated the EF phase as 'very, very hard' rather than 'hard,' indicating an increase in perceived effort by an entire category. Supported by: Partial funding from graduate student senate (GSS) monies for lactate supplies