Relaxin: How does it affect your exercise routine?

Many of us are familiar with the hormone relaxin. As the name implies, it’s responsible for relaxing several systems in your body in preparation for labor. What changes does this create in your body, and what can you do to keep yourself safe and active?

Relaxin levels in your body peak around 14 weeks and just before labor. It’s meant to prevent your uterus from contracting prematurely and sending you into early labor. As you may also guess, this hormone is what’s responsible for loosening your pelvis to make room for baby. However a hormone circulating through your blood won’t just affect one area: it’ll change your entire body! Here’s what you can expect:

In the first trimester, your body is busy growing a placenta. This organ will intertwine itself with your own blood vessels to pull supplies from your bloodstream and deliver to baby. And relaxin helps this happen! The hormone promotes growth of new blood vessels and causes vasodilation, or blood vessel expansion, throughout the body. The effects of this you may have noticed, for example lower blood pressure (manifested as lightheadedness), increased blood flow (aka the “pregnancy glow”), faster heart rate, and even stronger heart beats. What’s happening is your blood vessels have relaxed to increase blood flow to both the placenta and kidneys. This will provide more oxygen and nutrients to the fetus, and help clear waste out. Your body is a super machine right now, primed for max efficiency!

The two biggest impacts to your sports routine will be the changes in heart rate and blood pressure. Make sure to warm up slowly to let your body adjust to the increased metabolic demand. You can wear a heart rate monitor if you wish, or else just make sure you’re not pushing yourself to the point of feeling faint. Doctors used to recommend keeping your heart rate below 140 BPM while pregnant, but that has since been shown unnecessary. Read more about heart rate while pregnant here.

Muscles and ligaments
Not only do your blood vessels themselves relax: muscles, ligaments, and tendons throughout your body will too. You may notice this as a general sense of weakness or an inability to “push yourself” as much as usual. Tendons and cartilage become longer and less stiff. You may experience general instability in your shoulders, hips, knees, and ankles because of this. Some women find themselves clumsier than normal (yes, you’re not imagining it!) as everything in your body gets “looser”.

However it’s not all bad! Your body has an unparalleled ability to heal and regenerate itself right now. Relaxin prompts muscle fibers to regrow, helps heal muscles and ligaments, encourages bone growth, reduces inflammation, and promotes wound healing. It’s such a miraculous hormone that scientists are trying to use it to help heart attacks victims! And you have about ten times as much of this pumping through your body as usual. Pretty neat, huh?

The biggest challenge to your sports regime will be risk of injury due to the sudden increase in range of movement. One commonly injured ligament in pregnant women is the ACL in your knee. Avoid activities that put sudden stress on the knee, such as basketball, lots of jumping, or downhill skiing. You can pick them up again once the relaxin drops off at the 10-12 week postpartum mark.

It’s also important not to overstretch yourself. You will likely feel more flexible than usual while pregnant, which is great! When doing yoga or cranking through your stretch routine, be sure not to push yourself too far into the poses. It shouldn’t feel tight or painful. Even better, alternate between engaging the muscle and stretching it to safely preserve flexibility.

Birth canal
Finally, the one area we all expect to change with pregnancy and childbirth: the birth canal. As mentioned above, relaxin will cause ligaments in your body to soften. It turns out there’s one ligament that’s particularly susceptible to this: the pubic symphysis at the very front of the pelvis, which connects the left and right halves together. The uptick in relaxin just before labor will prompt this ligament to widen for birth. Relaxin also softens the vagina and cervix, both of which are made of fibers and muscle. Your entire pelvic area essentially becomes more elastic to fit baby through! All thanks to relaxin.

Relaxin has countless effects through your entire body, from relaxing blood vessels to relaxing muscles and ligaments. The biggest changes to be aware of while working out are increased ligament instability, increased joint and muscle flexibility, lower blood pressure, and higher baseline heart rate. These all have workarounds to keep you healthy and free from injury while exercising for two.