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First, know that there are several formulations and delivery methods for hormonal contraceptives (HC). HC includes the combined and progestin-only contraceptive pills, implants, contraceptive patches, progestogen injections, vaginal rings, and hormonal intrauterine devices (IUD). The most commonly used form is the oral contraceptive pill. Because the mechanism of action for the pill is to downregulate your natural hormones, the level of circulating sex steroids is dependent on the dose of synthetic hormones delivered in each pill. That means there can be a large variation in hormonal fluctuations between individuals taking oral contraceptives, which could impact skeletal muscle strength, hypertrophy, and protein metabolism.
Because hormonal contraceptives can put you in a heightened hormonal state, there are some potential physiological impacts. In general, we know that when it comes to strength training, the dose of the estradiol component of the pill affects skeletal muscle synthesis, but not strength. With regards to aerobic and anaerobic capacity, oral contraceptive pills are as- sociated with a decreased VO2 max peak, a decrease in the ability to adapt to high intensity training, and significantly elevated oxidative stress (that is not overcome by dietary antioxidants). From a metabolic standpoint, the pill is associated with less muscle protein synthesis (with greater protein catabolism), the synthetic progestin is known to stimulate appetite and increase visceral fat gain, and the estradiol component is known to increase circulating fatty acids at rest and during exercise (sparing glycogen, which may inhibit the ability to hit high intensities from a metabolic standpoint).
Above all else, when using hormonal contraceptives, it is difficult to keep track of how your body is adapting to load and energy needs, masking any irregularities in your menstrual cycle—which is typically the first sign that there is a misstep between training load/stress and energy intake. Ideally, it is best to first understand how each of the birth control formulations may affect you and then make an educated decision on which is the right one for your health needs. Understand that there could be an impact on your training and racing, and that to mitigate this you should increase your protein intake, incorporate plyometrics and multi-directional jumping into your gym routine to improve bone density, potentially adjust your training, and also increase anti-inflammatory foods in your diet. Lastly, be sure to talk to your doctor about the best form of birth control for your situation.