The number of women participating in sport competitions and/or recreational sport activities has increased considerably [1] and high intensity strength exercises are often listed as their preferred choice when it comes to improving physical conditioning [2]. However, our current knowledge on organic responses to physical exercise has been mostly built on the assessment of male subjects. According to Costelo et al. [1] only 4–13% studies in highly ranked sport science journals focused on women participants. Given this bias, exercise recommendations for women individuals are often based on sex-unspecific findings and on extrapolations of male responses to exercise that may not apply to female physiology [1], [3], [4], [5].

For women, it is suggested that monthly fluctuations in estrogen, progesterone and pituitary hormones influence muscle performance [3], [6], [7], [8], [9], [10] however, there are divergences between studies and, normally, only neuromuscuscular parameters are evaluated, remaining aspects of recovery and soreness lacking in best explanations.

These fluctuations in hormones define two phases in the menstrual cycle: follicular and luteal [2], [6]. The follicular phase is characterized by low serum concentration progesterone and by a low estrogen concentration at the beginning and high towards the end, where peak estrogen concentration is reached. During the subsequent luteal phase, progesterone serum concentration becomes high and estrogen secretion diminishes but remains relatively high [11], [12]. Physiologically, estrogen has been associated to an anabolic function, improving the intrinsic quality of skeletal muscles [2], [5]. On the other hand, a muscle catabolic effect has been associated to progesterone [2], [3].

Subjective muscle soreness and recovery scores after exercise are often used to evaluate individual responses to training, however, systematic changes that may occur during the menstrual cycle as well as their relationship with strength have not been evaluated. The potential influence of hormonal fluctuation on these scores might be more notorious between the menstrual and ovulation days. At the beginning of the follicular phase, the low concentration of estrogen is accompanied by menstruation, which will not be present at the end of the follicular phase, when ovulation occurs and the concentration of estrogen is high. The normal vaginal bleeding that occurs in the menstrual phase and the presence of pain perception fluctuations [13] may influence how women react to exercise and their responses to muscle damage.

Furthermore, if a contraceptive medication is used, the natural hormonal fluctuations associated with the menstrual cycle will be modified [[14], [15], [16]]. The contraceptive medication brand, type (monophasic, biphasic, etc.), and dosage (levels of estrogen and progestogen) may influence the estrogen protective effect on muscle damage process after an exercise [17]. In addition, the pituitary hormones (follicle stimulating hormone – FSH and luteinizing hormone – LH) [11], [12] are suppressed in women who take hormonal contraceptive pills. This suppression prevents follicular development and ovulation [18] and consequently reduces the secretion of endogenous estrogen and progesterone during the menstrual cycle [11], [12], keeping them at near constant levels throughout the cycle [8].

Considering the potential protective effect of estrogen, it has been suggested that women who take contraceptive pills present with lower levels of endogenous estrogen, and consequently are more susceptible to exercise-induced muscle damage [[8], [19]]. However, the interaction between hormonal contraceptive medication and responses to muscle damage in terms of strength recovery and pain at the menstrual and non-menstrual phases is still poorly understood.

The aim of the present study was to investigate the influence of menstrual phase and oral contraceptive (OC) on the strength loss, muscle soreness and recovery perception after an exercise protocol. Women were investigated during the beginning of the follicular phase (“menstrual” ∼the 1st or 2nd day) and during the end of the follicular phase, when ovulation occurs (“non-menstrual” ∼the 14th or 15th day). The relationships between peak torques and participants-reported parameters of muscle soreness and recovery were analyzed. We hypothesized that OC users (low estrogen level) present with greater strength loss and muscle soreness after a concentric/eccentric exercise protocol than non-users and this difference will not exist in the menstrual phase due to the natural low levels of estrogen in both groups.