Historically, research in physiology and sports performance has exhibited a marked bias towards the male population, both in study design and in the interpretation and application of results. This approach has relegated the biological specificities and needs of women to the background, perpetuating a significant gap in scientific knowledge. In the field of female physiology, research has been largely limited to reproductive aspects, overlooking the essential role of ovarian hormones in multiple physiological processes. The inclusion of women as study participants has been scarce, and in many cases, methodologies designed for men have been applied, thus rendering the particularities of female physiology invisible.1-3 In the few studies that include women in sports research, their specific hormonal variations are often overlooked, or testing is conducted during times of low hormonal levels to avoid potential interference.3,4

The natural fluctuations in the blood concentrations of the two female hormones, estrogen and progesterone, are essential for regulating the menstrual cycle (MC) and maintaining reproductive health. Estrogen, produced mainly in the ovaries, regulates the MC, secondary sexual development, and bone density.5,6 Progesterone, in addition to being crucial for reproduction, influences the nervous and immune systems and serves as a precursor to other steroid hormones.7 Both hormones affect mood, cognition, metabolism, and overall health throughout a woman's life.7 These natural fluctuations are under the control of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which are produced by the pituitary gland. FSH and LH blood concentrations are also cyclic, playing a key role in fertility, regulating the MC, ovulation processes, and estrogen production.8

Eumenorrhea refers to the presence of regular MC, indicative of a healthy hormonal and reproductive system.9 Methodologically, it is defined by cycles of 21–35 days, an LH surge, an appropriate hormonal profile, and the absence of hormonal contraceptives (HC) in the last three months.10 Menstrual irregularities, such as amenorrhea, an abnormal absence of menstruation, and particularly functional hypothalamic amenorrhea, are common in athletes and are often associated with the relative energy deficiency in sport (REDs) syndrome. .11–13 In athletes, amenorrhea is linked to hypothalamic hormonal changes that reduce LH pulsatility, suppress ovarian steroids, and maintain the pituitary response to Gonadotropin-Releasing Hormone (GnRH) .14

To address and manage these various menstrual irregularities, many women turn to HCs. These not only provide effective birth control but also offer significant benefits in regulating the MC and mitigating symptoms related to menstrual disorders. There are various HC administration methods, such as oral contraceptives (OCs), implants, injections, transdermal patches, vaginal rings, and intrauterine systems.15 A recent study with 430 female elite athletes revealed that 213 were using HCs, indicating that almost half did not present an eumenorrheic MC. Of these athletes, 145 (68 %) used OCs, making this the most common hormonal method.16 OCs can be combined (estrogen and progestin) or progestin-only, and are available in monophasic, biphasic, or triphasic formulations, with different hormonal combinations that affect the physiological response.16,17 The variability in the type and concentration of estrogen and progestin among different contraceptive preparations can significantly influence the body’s physiological response.16 OCs operate through a negative feedback mechanism on the hypothalamic-pituitary-ovarian axis, inhibiting the secretion of FSH, LH, and GnRH, thereby suppressing ovulation.18,19

Despite the high prevalence of OC use among athletes, there is a notable lack of research examining the effect of hormonal fluctuations within the OC use cycle on women's exercise responses.20 Most of the current literature has focused on evaluating physiological differences between OC users and non-users, or responses before and after starting their use.17 Furthermore, many athletes have adopted the strategic use of OCs to modulate or even eliminate menstrual bleeding, valuing the reliability and reversibility of contraception, along with the ability to mitigate the symptoms of a regular MC.18,21

Currently, the lack of high-quality data limits understanding of how hormonal variations from the MC or HC use influence exercise physiology,9,18,22,23 due to methodological issues such as inadequate menstrual phase verification, small sample sizes, and high intra- and interindividual variability. Although HCs could offer a more stable hormonal environment for investigating these relationships, most studies compare users and non-users without analyzing the phases of the use cycle.16 Current research suggests that aerobic performance, anaerobic performance, and strength may vary throughout the HC use cycle. Therefore, it is essential to conduct studies that analyze these variables in greater detail, using HCs as a framework to obtain more consistent and applicable results in the sports field.17 A deeper understanding of these effects is not only crucial for the development of strategies that promote athletes’ health and well-being but also for optimizing their sports performance. Addressing this research gap will allow for evidence-based recommendations, thereby improving athletes' ability to effectively manage their training and competition regimes according to their hormonal profiles. Therefore, the aim of this study was to investigate the influence of hormonal contraceptives on physiological responses and athletic performance in healthy young women and elite female athletes, comparing the effects during the active and non-active phases of hormonal contraceptive use. It was hypothesized that HC could significantly affect physiological responses and athletic performance, with superior outcomes expected during the non-hormonally active phase (NHAP) compared to the hormonally active phase (HAP). This difference is attributed to hormonal variations induced by contraceptive use, which alter the hypothalamic-pituitary-ovarian axis and, consequently, impact energy metabolism and muscle contractility—, especially in high-demand physical contexts.18,24,25

To evaluate the effect at the two moments of the HC cycle, HAP and NHAP, five physiological variables were analyzed: Pre-Lactate, Post-Lactate, Mean HR, Max HR, and Mean Power. These variables were evaluated through a submaximal performance test, allowing analysis of both pre and post-test values, as well as the mean and maximum values from the tests performed. The detailed results of each variable and their comparison between the two cycle moments are presented below, in Table 3.

In the analysis of Pre-Lactate, a mean of 1.2 (0.3) mmol·L−1 was observed for HAP and 1.4 (0.7) mmol·L−1 for NHAP. The mean difference between the two phases was 0.2 mmol·L−1 (-0.8 to 1.1), with a p-value of 0.61 and a moderate effect size (d ≈ 0.48). Regarding Post-Lactate, the mean was 8.5 (1.8) mmol·L−1 for HAP and 7.9 (3.5) mmol·L−1 for NHAP. The mean difference was −0.6 mmol·L−1 (-3.5 to 2.4), with a p-value of 0.76, and a small effect size (d ≈ 0.28). For Mean HR, a mean of 167 beats·min−1 (12.3) was recorded for HAP and 172 beats·min−1 (8.11) for NHAP, with a mean difference of 5.2 beats·min−1 (−6.7 to 17.1) and a p-value of 0.46, and a considerable effect size (d ≈ 0.71). For Max HR, the mean was 187 beats·min−1 (9.3) for HAP and 185 beats·min−1 (8.9) for NHAP, with a mean difference of −2.2 beats·min−1 (−15.8 to 11.4) and a p-value of 0.71, and a small effect size (d ≈ 0.34). Finally, for Mean Power, a mean of 259 W (20.9) was recorded for HAP and 260 W (22.7) for NHAP, with a mean difference of 1.0 W (−1.3 to 3.3) and a p-value of 0.94, and a very small effect size (d ≈ 0.07). None of the comparisons between variables reached a p-value < 0.05; consequently, no significant differences were found between HAP and NHAP. These results highlight the importance of considering both statistical significance and effect size to properly interpret findings.

In Fig. 1, the individual lines for each participant can be visualized, allowing for the observation of trends in each of the study variables between the active and non-active (placebo) phases. This representation makes it possible to identify whether there is a general trend in the subjects’ responses or if any participant shows a markedly different evolution compared to the rest. Thus, the figure facilitates the detection of potential individual patterns or outlier cases in the evolution of the physiological variables analyzed.

Fig. 1.

Individual comparison of physiological parameters between the HAP and the NHAP.

Note. The values shown correspond to the individual lines of each study participant at the two evaluation points for the different variables analyzed: Pre-Lactate, Post-Lactate, mean heart rate (Mean HR), maximum heart rate (Max HR), and Mean Power. Each line connects the measurements corresponding to each subject in the hormonally active phase (HAP) and the non-hormonally active phase (NHAP).

Finally, considering the small sample size of n = 5, the use of Cohen’s d is particularly valuable, as it provides standardized measure of effect magnitude. This can guide the interpretation of results beyond statistical significance and inform future research by helping to estimate the potential physiological impact and the sample size required to detect meaningful differences in similar studies.

The present research aimed to examine the influence of HC on physiological responses and sports performance in healthy young women and elite athletes, comparing the effects during the HAP and the NHAP. This study did not identify any physiologically significant differences in the parameters reflecting performance in a submaximal 2000-meter rowing ergometer test between the phases of the HC cycle. Our findings refute the proposed hypothesis that, during the NHAP, aerobic capacity, anaerobic power, and strength would be superior compared to the HAP in elite rowing athletes.

To compare the results of the present study with others, we considered the test or effort performed as aerobic-anaerobic due to the combination of duration, intensity, and observed lactate levels. Both energy systems are contributing significantly to completing the test. In this regard, some authors have shown that anaerobic power is affected by the phase of the HC cycle.27,28 These suggest that athletes who depend on the stretch-shortening cycle, such as jumpers and sprinters, could benefit from competing during HAP. However, the improvement in reactive strength performance during this phase remains poorly explained.28 Some studies have confirmed that estrogen levels can alter metabolism during acute exercise.29,30 An increase in estrogen concentration inhibits gluconeogenesis and glycogenolysis, which spares glycogen and increases the use of lipids as an energy source.29 On the other hand, in these modalities, some authors observed a reduction in peak blood lactate and an increase in pH during the NHAP (when progestogen is lower) compared to the HAP.29,31 Supporting this, recent studies showed that blood lactate was higher in the HAP compared to the NHAP,32,33 findings consistent with our results, though not statistically significant, but with a potential moderate/high size effect according to Cohen’s d. However, despite the statistical analysis, the physiological relevance of a 1 mmol/L change in blood lactate is likely minimal and could fall within the typical margin of error for this variable.32 This explanation of the difference in lactate values according to the cycle phase suggests that blood lactate may be influenced by factors such as buffering capacity and plasma volume, rather than changes in substrate metabolism due to variations in estrogen levels. An increase in circulating aldosterone during the NHAP could improve fluid and electrolyte retention, increasing plasma volume and buffering capacity. In short-duration and high-intensity efforts, exogenous steroids may not have sufficient time to significantly influence substrate metabolism or buffering capacity.29 In summary, current scientific evidence does not support a direct relationship between the phases of the HC cycle and blood lactate concentrations in anaerobic exercise.

On the other hand, regarding aerobic exercise, early authors investigating the effects of HC suggested that they negatively affected exercise performance and V̇O2max.34,35 Additionally, a longitudinal study reported a reduction in V̇O2max in moderately trained women after four months of using triphasic OC.24 However, more recently, other studies have demonstrated no differences in aerobic performance across different phases of the OC cycle in rowers33,36 and other sport modalities.37 Likewise, no statistically significant variations in blood lactate concentrations after exercise between these phases were observed.33 In addition, HR, pulmonary ventilation, and V̇O2 during aerobic endurance tests were not significantly affected by the hormonal cycle phase,33,34 findings that align with our results for average and maximum HR, although they were not statistically significant. Our findings point to metabolic and cardiorespiratory stability during aerobic exercise regardless of hormonal fluctuations due to HC use, and agree with recent reports studying oral contraceptive pills38 and the natural menstrual cycle.39

The present study analyzed the influence of HC on physiological responses and sports performance in healthy young women and elite rowing athletes. Our results did not reveal physiologically significant differences in performance parameters during NHAP compared to HAP. While some previous studies reported varying results, these discrepancies may be attributed to differences in the type of exercise, its duration and intensity, the performance level of the participants, and the type of HC used.

The main limitations of this study include the small sample size and the heterogeneity in the composition of contraceptives, as well as the lack of complete blinding and insufficient control of external factors such as diet and participants' mood, which may have introduced some degree of uncontrolled bias and affected the validity of the results. From a practical perspective, since the observed effects were mostly trivial and variable, no general recommendation can be made regarding the use or discontinuation of HC, highlighting the need for an individualized approach. To draw more definitive conclusions, future studies should focus on larger sample sizes and adopt randomized controlled longitudinal designs, which would allow for a more robust examination of the unresolved questions surrounding the effects of HC on athletic performance.