I've written way back in 2009 that women are more prone to ACL injuries compared to men during the time of the month because changing hormone levels affect ligament strength. The bad news is it's not just ligaments. Researchers found evidence that muscles, tendons, joint and ligaments were more affected across the menstrual cycle.
The English women's national football team (from under-15's to the senior squad) were studied over a four-year period for this study. Injuries during training camps and competitions were tracked. Only players with regular menstrual cycles and not on hormonal contraceptives were included in the analysis. 156 injuries from 113 players were recorded.
The key finding seems to be that estrogen has broad effects on decreasing stiffness of ligaments and tendons. While this is may be helpful during childbirth, it also make your knees, ankles and other joints less stable when estrogen levels are higher.
My wife explains that at the start of menstruation (which is the follicular phase), estrogen is lowest. Estrogen levels begin to rise to a peak shortly before ovulation (luteal phase). It then drops sharply, before rising again to a gentler peak during the luteal phase.
Bearing the above in mind, ACL injuries tends to be more likely during the late follicular phase where estrogen levels tend to be highest and ligaments tend to be loosest. During this phase, knee joints get one to five millimeters looser (Chidi-Ogbolu and Baar, 2018).
It can be that tendons that have became looser or more lax may actually decrease injuries to the muscles since they may be able to absorb some of the impact from forces that may strain or tear a muscle (Chidi-Ogbolu and Baar, 2018).
The analysis showed that muscle and tendon injuries were about twice as likely during the late follicular phase (higher estrogen levels leading to lax muscles and tendons) compared to other phases.
Joint and ligament injuries were significantly less during the late follicular phase (24 in total). Quite the opposite of the study's hypothesis (lax ligaments bad, lax tendons good).
An interesting note was that 20 percent of the injuries happened when a player's menstrual cycle was late or overdue (based on when the players expected their next period to start). This may be due to the "female athlete triad", which involves persistent calorie deficits and can lead to missed or irregular periods, lower bone density and increased overall injury risk.
Some of you reading this may be planning to avoid contraceptives during training and then using them during during the competition season since hormonal contraceptives can be protective of ligaments (since they suppress the higher peaks in estrogen). Beware of the trade-offs though, higher estrogen levels help promote muscle building and repair muscles and tendons in response to training.
It is clear that hormonal fluctuations matter although clearer guidelines on the menstrual cycle may be needed since knowing estrogen can affect injury risk may not pan out totally in the real world.
My suggestion would be to track and record your periods so you are aware of what factors can and may be at training/ competition. Knowledge is certainly power in this case.
More research is definitely needed and you'll be the first to know the latest information when you read it in our blogs.
References
Chidi-Ogbolu N and Barr K (2019). Effect Of Estrogen On Musculoskeletal Performance And Injury Risk. Frontiers Physiol. 9: 1834. DOI: 10.3390/fphys.2018.01834.
Martin D, Timmins K, Cowie C et al (2021). Injury Incidence Across The Menstrual Cycle In International Footballers. Frontiers in Sp Active Living. DOI: 10.3389/fspo.2021.616999.
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