Relaxin is a hormone produced by the ovaries and placenta. In males it is produced in the prostate and is present in the semen. Relaxin is thought to have a role in sperm motility, fertilization, implantation, uterine growth, and even facilitating labor. During pregnancy, relaxin is at its highest levels as the first trimester transitions into the second trimester, and then also at birth. Relaxin is also known to stay in a woman’s body until breastfeeding has stopped but at lower levels.
Relaxin has a legit effect on ligaments and connective tissue. Relaxin alters the properties of cartilage and tendons by activating the enzyme collagenase, which is involved in bone remodeling and healing connective tissue.
Relaxin is definitely needed. We have four different types of tissue: nervous, muscular, epithelial, and connective. The connective tissue is the most abundant and helps to hold our body’s contents in place. We have connective tissue throughout our pelvis and between our ribs. The effects of relaxin can therefore be seen in these areas the greatest. Imagine how difficult it would be for our bodies to adapt if we did not have relaxin.
Relaxin is also a vasodilator. This helps to keep mother’s blood pressure in check with the increased blood volume.
So, we can all agree on the fact that relaxin is important and universal intelligence definitely supports its presence.
However. I’m just not sold, yet, that it can lead to injury in pregnant women (or even an injury in women on their menses) or predispose to a musculoskeletal injury. And, I’m a woman that tore my ACL while on my period. There are definitely some studies that would support the theory that a woman’s cycle and the phase she’s in can predispose her to injury. However, there are a number of variables (like hormonal therapy for a woman with higher relaxin levels) that come into play, and a lot more research is needed to make that claim.
My thoughts are this: we definitely need more research in regard to women’s cycles and pregnancy and the effect on the musculoskeletal system. I’d be curious to see the movement patterns - and maybe lack of posterior chain involvement - in those athletes that tear their ACLs while on their periods . Glute strength and our posterior chain definitely help to stabilize the pelvis, which in turn is going to help optimize knee function and would decrease the risk of an ACL injury. The same correlation between movement patterns and body awareness can be applied to the pregnant athlete.
The women that have been training and continue to train during their pregnancy likely have enhanced proprioception (body awareness) and joint stability; therefore, they have a better foundation from which to train (heightened sensorimotor and somatosensory functions). Those women that have not been training are likely at an increased risk for musculoskeletal injury, whether they’re menstruating, pregnant, or not.
Personally, I take it easy or dial down the intensity when it’s my time of the month , or it’s about to be. The Universe just tells me to slow it down. The same goes for the BIRTHFIT prenatal training. We dial the intensity and load down sometimes as early as 32-34 weeks for mama, depending on mama.
Running and jumping are usually the first movements to feel less comfortable during pregnancy (and sometimes the last to return after baby). You have to know that it’s your body accommodating for a growing baby and organ. Our bodies know what to do. It appears that relaxin levels vary from woman to woman and definitely affect some women more than others.
Relaxin is a hormone to be aware of and respect. It is a natural player in the human body. Embrace it rather than fear it. Rather than fearing injury due to a naturally occurring hormone, we recommend reaping the benefits of exercise during pregnancy. Continuing to train (smart) during your pregnancy is likely to make you MORE aware and comfortable with your body. Overall, exercise for mom and baby has numerous benefits, and even ACOG agrees that exercise is good for mom and baby!