WRITTEN BY: JERICA MOORE MA, ATC
In a recent study, women were asked if they believed their menstrual cycle affected their training and performance. Bruinvels et al. found that out of 90 subjects, 51% answered yes. Dysmenorrhea (painful periods), which is characterized by painful menstruation, nausea, headaches, fatigue, and diarrhea, is experienced by 60-91% of women who do not use hormonal birth control and may affect athletic performance. Despite this, very little is known about menstrual cycle related side effects and what their influence on training and athletic performance is. Martin et al. shows approximately half of elite female athletes (n=430) use a form of hormonal birth control (HBC) to predict and/or manipulate the timing, frequency, and amount of menstrual bleeding. These results highlight the importance of understanding the effects of the menstrual cycle and hormonal birth control use in female athletes.
This is a very complicated area of research due to the abundance of HBC formulations currently on the market. HBCs provide a consistent cycle by systemically controlling the concentration of endogenous sex hormones, by reducing the natural production of estrogens and progesterone. Today, mainly monophasic and triphasic HBCs are prescribed, with the use of biphasic decreasing. This figure, from Burrows et al. shows the cyclic pattern of estrogen and progestins in (a) monophasic, (b) biphasic, and (c) triphasic HBCs. Monophasic pills provide fixed doses of estrogen and progestin over 21 days, followed by 7 days of a placebo. Biphasic pills have a fixed amount of estrogen but two different strengths of progestin. Triphasic pills contain three different doses of estrogen (or sometimes progestin) that are increased throughout the cycle. Depending on the brand, the dosage of these exogenous hormones varies greatly. Therefore, just as the hormone fluctuations between two women differ greatly, there appears to be large inter-individual variability between hormones administered through HBC and their effects on performance. HBCs can also be classified by type: combined (estrogen and progestin) or progestin-only. The type and concentration of estrogen and progestin varies between the different chemical formulations and may influence the physiological response. As the level and fluctuation of hormones are believed to be a possible factor in performance, it is important to understand the effect of administering the various types and forms of HBC to female athletes. Some of the more well studied areas of HBCs effect on athletic performance are body composition, core body temperature, aerobic capacity, and muscle strength.
HBC has been shown to increase body mass in women – both in monophasic and triphasic formulations. Triphasic HBCs have also been shown to increase fat mass that could be detrimental to performance. Increases or decreases in body mass may be dependent not only on the HBC administered, but also the potency and androgenic effects of the progestin within the HBC. More research is needed in this area, but progestin has been shown to have independent effects on water regulation. This may suggest that the higher potency of the HBC formulation, the more exacerbated the effects may be. A lot of these studies report “non-significant findings” which in an athletic situation may be meaningful if the athlete relies on minimizing body mass. For example, a weight increase of 1kg for a weightlifter may be significant in the ability to make weight or maintain her current weight class. That slight increase in body mass may not be significant to others, but it is in this situation.
Core Body Temperature
Studies show that regardless of the amount of progestin contained in HBC or the type of HBC used, core body temperature is affected. Any increase in core body temperature due to HBC use could be detrimental for an athlete – it could predispose the athlete to an increased risk of heat illness, particularly in long duration events (>60 minutes) in hot, humid environments. Even in a natural menstrual cycle, there is a notable increase in core body temperature due to the elevated levels of progesterone that occurs during the luteal phase. Athletes and coaches both need to be aware of this and be cautious in those training environments.
The effects of HBC on aerobic capacity are more pronounced in triphasic formulations than in monophasic formulations – athletes may be advised to use monophasic HBC instead of triphasic in events where aerobic capacity is important. Aerobic capacity is impaired by triphasic HBC because of the blunting of the sympathetic nervous system by the high ovarian hormone concentrations of HBCs – many studies have reported a decrease in VO2peak. Because monophasic formulations regulate the hormones to a steady state, one would hypothesize that the controlled environment would minimize any potential variations in physiological variables – more research is needed in this area.
Fluctuations in strength throughout a regular menstrual cycle have been linked to estrogen exerting a positive effect on skeletal muscle function, and progesterone inhibiting the effects of estrogen. The progestin prescribed in the HBC is what determines the effect of the estrogen. Since the progestin content in the different varieties of HBC differ in potency and androgenic effects, the effect of estrogen also varies. However, it seems that various forms of HBC do not produce enough of an androgenic effect to influence strength among female athletes. The data on HBCs effect on muscular strength and performance is minimal and inconclusive.
Women use HBC for a multitude of reasons – specifically, the majority athletes use it to prevent the negative side effects (e.g. PMS) that come with a menstrual cycle. It is critical for a female athlete who is considering taking HBC to consider, along with her physician and coach, the formulation of HBC and its potential effect on health and specific performance variables. It should also be noted that addressing the underlying issues is important for all females who desire a healthy, normal menstrual cycle. HBC is most often prescribed as a treatment option, but there are alternatives to consider to fix the root cause of undesirable symptoms associated with menstrual cycles.
Bruinvels, G., Burden, R., Brown, N., Richards, T., & Pedlar, C. (2016). The prevalence and impact of heavy menstrual bleeding (menorrhagia) in elite and non-elite athletes. PLoS One, 11, e0149881.
Burrows, M., & Peters, C. E. (2007). The Influence of Oral Contraceptives on Athletic Performance in Female Athletes. Sports Medicine, 37(7), 557-574.
Martin, D., Sale, C., Cooper, S., & Elliott-Sale, K. J. (2018). Period Prevalance and Perceived Side Effects of Hormonal Contraceptives and the Menstrual Cycle in Elite Athletes. International Journal of Sports Physiology and Performance, 926-932.
Rechichi, C., Dawson, B., & Goodman, C. (2009). Athletic Performance and the Oral Contraceptive. International Journal of Sports Physiology and Performance, 4, 151-162.