Emily E. Bechke1, Mitchell E. Zaplatosch1, Samantha J. Goldenstein1, Laurie Wideman, FACSM1, William M. Adams, FACSM2. 1University of North Carolina-Greensboro, Greensboro, NC. 2United States Olympic & Paralympic Committee, Colorado Springs, CO.

Background: Assessment of autonomic nervous system (ANS) function through measures of heart rate variability (HRV-parasympathetic tone) and systolic time intervals (STI-sympathetic activity) can serve as noninvasive indices to determine health status and day-to-day physiological readiness for exercise. As the use of noninvasive measures become increasingly prevalent in research and guided training, it is important to know if menstrual cycle phase influences these metrics. Therefore, the purpose of this study was to determine the impact of menstrual cycle phase on autonomic function as indicated by HRV and STI. Methods: Seventeen naturally cycling females (age, 24±5yrs; ht,163.3±7.3cm; mass, 71.3±24.4kg, body fat, 22.7±9.3%) visited the laboratory on days 5 (early follicular; EF), 13 (late follicular; LF), and 20 (mid-luteal; ML) of their menstrual cycle; day 0 was defined as the onset of menstruation. HRV and STI were measured in a seated position for 6-minutes using electrocardiography and impedance cardiography, respectfully. HRV analysis was performed on the last 5-minutes of each segment where heart rate (HR), root mean square of successive R-R intervals (rMSSD), high frequency power (HF), and sample entropy (SampEn) was assessed. STI analysis was performed during a 30-second window within the last 5-minutes of the segment and used to indicate the pre-ejection period (PEP) of the heart. HRV measures were log transformed (ln) due to a normality violation, as indicated by a Shapiro-Wilk test. Separate repeated measures ANOVAs were used to determine differences for each HRV and STI metric across EF, LF, and ML. Results: There were no significant differences in HR [bpm; EF, 73±12; LF, 69±13; ML, 73±11; p=1.0], lnrMSSD [ms; EF, 3.7±0.5; LF, 3.7±0.5; ML, 3.64±0.5; p=0.88], lnHF [ms2; EF, 6.3±1.2; LF, 6.3±1.1; ML, 6.2±1.0; p=0.97], SampEn [EF, 1.4±0.4; LF, 1.5±0.4; ML,1.6±0.3; p=0.35], or PEP [ms; EF, 1.2±0.1; LF, 1.2±0.1; ML, 1.2±0.1; p=0.33] across the menstrual cycle. Conclusion: Measures of HRV and STI did not differ across the menstrual cycle in naturally cycling females. However, it should be noted that menstrual cycle phase was not confirmed with multiple methods (i.e., basal body temperature, hormone levels, ovulation tests). Given the significant inter-individual variation in menstrual cycle in females, future research should take a multilevel approach to confirm menstrual cycle phase.

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