The menstrual cycle is an important biological rhythm, whereby large cyclic fluctuations in endogenous sex hormones, such as estrogen and progesterone, are observed, which can affect performance. Evidence shows that endogenous and exogenous changes in hormone concentrations during the menstrual cycle exert many effects on the nervous and endocrine systems, in addition to the connective tissue, with consequences for the movement system. Pre-clinical studies (i.e., in animal models) show an estrogen association with the structural and mechanical properties of tendons and ligaments. Several elegant studies performed with female participants have tried to establish the mechanism underlying the effect of estrogen on collagen synthesis and its effects on exercise and functionality. Their findings suggest that the tendon properties may be affected when exposed to varying concentrations of estrogen. The largest tendon in humans, the Achilles tendon, has a direct role in functional capacity, activities of daily living, and locomotion. Studies show that the triceps surae's structural and mechanical properties may change throughout the menstrual cycle, and that these changes are related to endogenous and exogenous fluctuations in estrogen and progesterone. Musculotendinous stiffness, which is dependent on the collagen content, has been seen to vary considerably over the course of the menstrual cycle. In addition, it has been reported that females who have been taking the contraceptive pill for at least a year demonstrate lower levels of tendon strain compared to non-pill taking females, indicating a possible influence of hormonal state on tendon mechanical properties. However, the different experimental designs, the varied approaches to the evaluations and the lack of studies with high methodological quality limit our understanding of the effects of the different phases of the menstrual cycle on the triceps surae's neuromechanical properties. The aim of this observational study will be to investigate whether the morphological, mechanical (active and passive), material, and functional properties of the plantar flexor muscles and of the Achilles tendon, as well as functional parameters, change during voluntary contractions throughout the phases of the menstrual cycle in eumenorrheic women and in users of hormonal contraception. Understanding the acute effects of these properties in eumenorrheic women and users of hormonal contraception is essential so that we can adequately plan interventions and prescriptions of physical exercise and rehabilitation aimed for women.

Inclusion Criteria:

• Inclusion criteria for the group of eumenorrheic women

  • Being eumenorrheic with a regular menstrual cycle lasting between 21 and 35 days during the last 6 months prior to study participation.
  • Body Mass Index between 20 and 25 kg/m2.
  • Normal ankle function and range of motion.
  • Do not use hormonal contraception of any kind or supplements hormones for at least the 6 months prior to the study.
  • No complaints of pain or history of lower limb injury.
  • In view of the COVID-19 pandemic, have completed vaccination will be used as an inclusion criteria.
  • For the physically active group, practice regular physical exercise at least 3 times a week for the past 6 months.
  • For the sedentary group, not practicing regular physical exercise in the last 6 months.

Inclusion criteria for the group users of hormonal oral contraception:

• Body Mass Index between 20 and 25 kg/m2.
• Normal ankle function and range of motion.
• Make use of any method of oral hormonal contraception (compressed).
• Make use of combined oral hormonal contraception with estrogen and progesterone (ethinylestradiol + Drospirenone) for at least 6 months before participating in the study.
• Do not use other hormone supplements for at least 6 months prior to the study.
• No complaints of pain or presence of pathologies in the lower limb
• In view of the COVID-19 pandemic, have completed vaccination will be used as an inclusion criteria.
• For the physically active group, practice regular physical exercise at least 3 times a week for the past 6 months.
• For the sedentary group, not practicing regular physical exercise in the last 6 months

Exclusion Criteria:

Exclusion Criteria for eumenorrheic and contraception hormonal groups:

Health problems - contraindication to maximal effort exercise. Additionally, the following subjects will be excluded:

• Women who have anovulatory cycles or phase lutea deficiency.
• Women in early menopause.
• Pregnant or lactating women.
• Women with oligomenorrhea (menstrual cycles longer than 35 days, or delay of menstruation for the same period).
• Women with hypothalamic amenorrhea.
• Female smokers.
• Women with metabolic syndrome.
• For women using hormonal contraceptives, women who use adhesive, injectable, intrauterine devices, implants, vaginal rings, as well as progesterone-only CH methods.
• Does not meet the inclusion criteria.

Over the last three decades, there has been a rise in the number of women participating in exercise, from physical activity to elite sports. However, the number of studies regarding female participants' performance is still small compared to male participants. The menstrual cycle is an important biological rhythm, whereby large cyclic fluctuations in endogenous sex hormones, such as estrogen and progesterone, are observed, which can affect performance.