Birth control pills and intense training: debunking a myth about muscle recovery

Health and Wellness 17. dec 2023 3 min PhD student Mikkel Oxfeldt Written by Morten Busch

A new study shows that second-generation birth control pills do not affect muscle recovery among female athletes, contrary to what previous studies have indicated. For the first time, the new study examined muscle recovery among athletes rather than untrained females. This study is important for athletes and coaches since it alleviates concerns about how birth control pills affect muscle recovery, contributing to a new understanding of the way hormones affect how the body processes intense training.

The ability to recover quickly after physical exertion is critical for athletes. For years, there has been concern that birth control pills could negatively affect this process. A new study challenges these previous assumptions on how second-generation birth control pills affect muscle recovery. This research is a significant step in understanding how birth control pills really affect athletes’ performance and health.

“Our research demonstrates that concerns about how birth control pills affect recovery are unfounded. Females can use second-generation birth control pills without fear that it will prevent them from properly recovering after intense training,” explains a researcher behind the study, Mikkel Oxfeldt, PhD Fellow from the Department of Public Health at Aarhus University.

One less thing to worry about

The study involved 40 trained females, with half using second-generation birth control pills and the other half not. They underwent strenuous training, followed by evaluations of muscle strength measures, jumping height and muscle soreness. Blood samples were collected before and 3, 24 and 48 hours after training to assess muscle damage markers. The participants also received individualised diet plans to support recovery.

“This study is the first and largest to examine how birth control pills affect muscle recovery among trained females, focusing on second-generation pills, the most frequently used in Denmark. Our study compared the recovery rates between females and revealed that the muscle recovery process was similar between groups, indicating that using second-generation oral contraceptives does not significantly affect the recovery of muscle after strenuous exercise,” asserts Mikkel Oxfeldt.

The ability to recover quickly between training sessions is one tool needed for elite athletes to succeed. In fact, poor recovery can make or break a career given its key role in maintaining peak performance throughout a season with a high training load.

“In a competitive situation, such as the IHF Women’s World Championship in handball that is wrapping up right now, games are often very close together in a final round. This necessitates rapid recovery between games to maintain world-class performance. In situations like this, there is reason to be aware of all factors that can influence recovery. With the new knowledge on birth control pills, athletes and coaches now have one less thing to worry about,” explains Mikkel Oxfeldt.

The surprising effect of estrogen on skeletal muscle

The primary reason the researchers delved into this topic was because in previous experiments the sex hormone estrogen has been shown to have many positive effects, both on muscles and on the cardiovascular system.

“If we remove ovaries from a mouse, meaning that it does not produce estrogen at all, and we then give it estrogen, then you can see a quite potent muscle response,” says Mikkel Oxfeldt.

Mice given estrogen and undergoing induced muscle damage can regenerate their muscles to a much greater extent than the group that does not have it. This suggests that estrogen plays a critical role in the muscle.

When females take birth control pills, their bodies’ own production of estrogen and other female hormones is vastly reduced, and the synthetic hormones provided from the birth control pill now take over. Knowledge is limited on how these synthetic hormones affect a tissue such as skeletal muscle.

Previous studies in this area have indicated that birth control pills negatively affect recovery – among untrained individuals. They indicated that birth control pill users have a greater increase in markers in the bloodstream for muscle damage after very intense work.

“The studies conducted so far have focused on untrained individuals, and this appears to make a difference. Untrained individuals experience a greater increase in markers for muscle damage, a larger functional decline in muscle strength and longer recovery time after physical exertion compared with trained individuals. Given this discrepancy in the response to exercise, we were not sure whether trained individuals would experience the same effect of taking birth control pills,” explains Mikkel Oxfeldt.

Even less is known about newer preparations

In traditional birth control pills, the hormone is in a different chemical form, ethinylestradiol, and not the natural form of estradiol. The natural form is easily absorbed through the mouth but is completely broken down in the liver on the way through the body and is therefore almost ineffective.

“Putting a chemical group on the hormone’s 17th carbon atom blocks that breakdown, but the hormone still works – at least as contraception. Despite the frequent use of birth control pills, we still lack knowledge about how they affect the body’s systems. The amount of research – and especially the quality of the current research – is insufficient,” asserts Mikkel Oxfeldt.

The researchers’ mission is therefore to conduct state-of-the-art research so that females can be guided based on a strong body of evidence. The study therefore contributes valuable knowledge about the use of hormonal contraception to sports science and females health. However, the study focused on second-generation birth control pills, so the effect of other contraceptive methods is an open question.

“Some birth control pills use hormone forms that are more similar to the natural form of estradiol, including newer generations of birth control pills, but alternative methods such as mini-pills and intrauterine devices are also gaining popularity. Although the use of these types of contraception is increasing, even less is known about these types of preparations,” says Mikkel Oxfeldt.

The researchers therefore plan to continue research to explore the effects of different types of hormonal contraception.

“We hope to be able to create more knowledge within the field in the coming years, and we will continue to explore this field to ensure that we understand all aspects of the menstrual cycle and how hormonal contraception affects females health and athletic performance,” emphasises Mikkel Oxfeldt.

Influence of 2nd generation oral contraceptives on muscle recovery following repeated resistance exercise in trained females” has been published in Medicine and Science in Sports and Exercise. The study received funding through the Novo Nordisk Foundation’s grant of 100 million Danish kroner to Team Denmark to strengthen Denmark’s competitiveness in international elite sports and create new knowledge about physical activity that can also benefit the general population.

Mikkel Oxfeldt is a PhD student at Aarhus University, Department of Public Health, investigating the impact of endogenous and exogenous female sex hor...

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