Author(s): Nuria Romero-Parra^1,2, Víctor M. Alfaro-Magallanes^2,3, Isabel Guisado-Cuadrado², A.C. Hackney⁴, Rocío Cupeiro², Ana B. Peinado².

Affiliations:
¹Department of Physical Therapy, Occupational Therapy, Rehabilitation and Physical Medicine, Faculty of Health Sciences, Universidad Rey Juan Carlos, Madrid, Spain;

²LFE Research Group, Department of Health and Human Performance, Faculty of Physical Activity and Sport Sciences (INEF). Universidad Politécnica de Madrid, Spain;
³Institute for Sustainability & Food Chain Innovation (ISFOOD), Navarra Institute for Health Research (IdiSNA), Department of Health Sciences, Public University of Navarra, Pamplona Spain.

⁴University of North Carolina, NC, USA.

PURPOSE: The testosterone and estrogen ratio (T/E) has been previously related to overtraining and proposed as a predictor of muscle damage, especially in eumenorrheic females after long-distance running competitions. This study aimed to explore changes in T/E throughout the menstrual cycle (MC) and its relationship with muscle damage after an eccentric-based resistance exercise.

METHODS: Nineteen eumenorrheic resistance-trained females participated in this study (28.6±5.9 years of age, 163.4±6.1 cm height, 59.6±5.8 kg body mass). Baseline serum estrogen and testosterone were measured in the early follicular, late follicular, and mid-luteal phases (EFP, LFP and MLP) of the MC, prior to a resistance exercise consisting of 10x10 plate‐loaded barbell parallel back squats (60% 1RM), with a tempo of 4s for the eccentric phase, 1s pause, and 1s for the concentric phase. Serum creatine kinase (CK) was measured 48h post-exercise in each phase. A one-way repeated measures ANOVA was performed to compare T/E between MC phases while Pearson correlations explored the relationship between T/E and CK concentrations.

RESULTS: A MC phase effect was observed for T/E (F=15.9; p<0.001; η²p=0.47); i.e., the ratio being significantly greater in the EFP (0.010±0.008) in comparison to the LFP (0.002±0.001, p=0.005); and MLP (0.003±0.003, p<0.001). However, correlations between these ratios and post-exercise CK (154±70, 195±95 and 172±86 U∙L^‐1 respectively for the EFP, LFP, and MLP) were non-significant (p>0.05), although a significant trend was observed between T/E and CK in

the EFP (r=0.50, p=0.07; moderate strength association).

CONCLUSION: A higher T/E ratio was observed in the EFP in comparison to the LFP and MLP in eumenorrheic females. Furthermore, a moderate correlation (approaching significance) between T/E and post-exercise CK was observed only in the EFP. Therefore, for strenuous eccentric exercises (back squats), the T/E could not be warranted as an adequate predictor of post-exercise muscle damage as denoted by CK changes. However, the T/E relationship with other muscle damage markers (e.g., strength loss), as well as to control for the study limitations herein (e.g.,

infrequent blood sampling) should be studied in future research.

Disclosures: Grant DEP2016-75387-P funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”.