Do Birth Control Pills Make You Slower? w/ Dr. Kelly McNulty - Science of Getting Faster Ep.10

Almost half of elite female athletes are hormonal contraceptive users. But do we know the impact they have on performance? Dr. McNulty joins us to shed light on this enigmatic topic in exercise physiology. In this episode of the Science of Getting Faster Podcast, Dr. McNulty outlines our contraceptive options, what these contraceptives are made up of, and how they impact our natural hormonal environment. Ultimately, this episode helps women and their coaches make informed decisions as it relates to their physiology and performance.

Join us tomorrow at 8am PST:

Instagram: @periodoftheperiod

Twitter: @kellymcnulty

The Effects of Oral Contraceptives on Exercise Performance in Women: A Systematic Review and Meta-analysis


  • (0:50) Different types of contraceptives available to women
  • (9:28) Most commonly used hormonal contraceptive and prevalence in the athletic population
  • (10:43) Why do the athletic population
  • (14:00) How the oral contraceptive pills impact a women’s natural hormonal environment?
  • (19:30) Is the withdrawal bleed that is experienced on the oral contraceptive pill equivalent to natural menstrual bleeding? Why is this important to keep in mind in the athletic population?
  • (20:30) Are there risks to chronic down regulation of a women’s own endogenous hormones, via the oral contraceptive pill?
  • (21:32) How do our different sex hormones impact exercise physiology?
  • (24:58) Is our exercise performance impacted by the phase of the menstrual cycle?
  • (31:08) What comparisons were made to determine the impact of Oral Contraceptives on performance?
  • (37:05) The results!
  • (40:40) What does Dr. McNulty recommend for finding a hormonal birth control that works well for you?
  • (46:40) Does the oral contraceptive pill impact strength and endurance performance differently?
  • (47:30) What research is missing on female athletes?

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Sharing this with my female riding/racing friends as they are always keen on more info around this.

Their answer to this question would be an eye roll plus “A lot, not all of it, but maybe most of it is missing.”


IUD data would be useful. Mirena’s got a lower circulating hormone level and the Paraguard has no hormone.

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Even as a bloke I found this interesting. Will pass it onto my female friends.

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Thank you for this podcast!! It was super informative. Love to see more femme-related topics on the Forum, as it seems that >80% of the posts come from males. :slight_smile:

As a personal anecdote, I went through a year of training on birth control, and since that two years of training with no oral contraceptives. Both years were similar in training consistency and I can definitely say my body responds better without taking an oral contraceptive. My body also holds on to less fat when not taking a COC - I can shed weight relatively easy if I am mindful about it. I do think there is truth to training with your cycle (follicular vs luteal), and as a female give yourself a little grace during your luteal phase, because you will come back even stronger during the follicular.
(refs: How to Exercise in Each Phase of Your Menstrual Cycle, Effects of follicular versus luteal phase-based strength training in young women - PMC)

Now I am in a lucky spot where I have long cycles (38 days) with short med/light periods - likely due to the fact that I am an endurance athlete. I can see why women with more painful/heavy cycles would want to take COC’s to alleviate them. Note: I am by no means a medical professional, and this is all anecdotal - though I have an extensive education/background in the biomedical and public health field and have done lots of research into the topic.