Aching knees? Don’t blame the weather–check your cycle instead. The muscles in your knees work differently at different points in your menstrual cycle, according to a study presented at the Integrative Biology of Exercise Conference. This changing muscle function destabilizes your joints and can set you up for serious pain.
Since women tend to suffer more ACL tears and generalized knee pain than men, researchers have long wondered if part of the reason has to do with hormonal changes from the menstrual cycle. “We know that progesterone and estrogen affect how the nervous system functions, so we theorized that the menstrual cycle might be affecting how women use their muscles,” says study author Matthew Tenan, certified athletic trainer and doctorate candidate.
Tenan and his research team at the University of North Carolina-Chapel Hill tracked the menstrual cycles of seven female volunteers with natural cycles (no hormonal contraception was used). Then they measured the activity of muscles in their knees during a knee extension exercise. They found that the firing rates of the muscle fibers were significantly higher later in the women’s cycles, about a week before their next period, compared to earlier in the menstrual cycle.
Blame it on hormones and the brain: “The way the brain activates the neurons that cause the muscle to move are altered specifically at the latter part of the cycle right before start of next period, when the progesterone is decreasing and estrogen levels are maintained,” says Tenan.
But don’t let the stages of your cycle influence your gym patterns, at least not yet.
“We can’t say for sure that there is the time in a woman’s cycle that she’s more likely to be injured, but the fact that the patterns of muscle firings change through the cycle could mean that there is less stability in the joint due to the muscles being activated in a different way,” says Tenan.
Understanding how the menstrual cycle influences women’s muscles can help trainers better treat knee pain in their patients in the future. “Some say women have more knee pain because they have wider hips,” says Tenan “But you can’t change the width of someone’s hips. Our findings are good news because people change their hormones all the time.”
Your knees aren’t the only body part affected by your period. Learn when your female hormones can help (and hurt!) you at the gym, so you know when you push harder, and when you can back off without guilt.
Image: Photodisc/Thinkstock
More from WH:
How to Avoid Sprains, Strains, and Tears
The Best Yoga Poses for Your Knees
Common Fixes for Fitness Class Injuries
Look Better Naked: Buy the book to learn how to look (and feel!) your very best.
