Hormone Relaxin and Running: What Every Mama Needs to Know

The hormone relaxin and running seem to be at odds but they don’t have to be. Relaxin makes women’s joints and muscles lax and unstable during pregnancy and postpartum (including for the duration of breastfeeding). But proper precautions such as core strength and running on smooth surfaces can minimize risk of injury. Read on to learn everything you need to know about the hormone relaxin and running. 

Woman running hard with a jogging stroller.
The hormone relaxin and running can go together well if you work on stability and strength.

I remember when I was first pregnant, I worried that relaxin would make my joints feel lax and my body feel wonky—and I would get injured! But these worries were unfounded. In fact, most women will not feel the effects of the hormone relaxin on their running. But that doesn’t mean you should ignore it.

In fact, studies show that relaxin can put pregnant women at risk for injuries—definitely not something you want as an expecting mother (and as a runner, I might add!). Thankfully, there are steps you can take to reduce your risk of injury while running with the relaxin hormone during pregnancy (and relaxin breastfeeding).

Download My Free Postpartum Running Plan

I got with Kate Baird, a doctor of physical therapy at the Hospital for Special Surgery, as well as dove into the research, to share all you need to know about the hormone relaxin and running.

side by side image of Whitney Heins in both of her pregnancies in workout clothes
I was able to run during both my pregnancies and postpartum when breastfeeding without experiencing the negative impacts from relaxin. Thank goodness.

Note: I am a running coach, not a doctor. Pregnant runners should talk with their healthcare providers about their running plans and listen to their bodies during pregnancy as every pregnancy and postpartum experience is unique!

Ok, let’s go!

What is relaxin? 

Relaxin is a hormone produced by the ovaries during the menstrual cycle, and the placenta during pregnancy. During a menstrual cycle, relaxin relaxes the uterus and prepares the uterine lining for implantation and prevents contractions, explains Baird.

During pregnancy, relaxin aids in loosening and relaxing the muscles and ligaments to prepare the body for growth of fetus and childbirth. This is perhaps its most famous role—and why people think of pregnancy and relaxin together, despite it being prevalent during the menstrual cycle, too.

relaxin and running tips pin
Relaxin can put pregnant and postpartum runners at risk for injuries. Pin these tips to stay injury-free.

Effects of relaxin on the body

The relaxin hormone does a lot to help the body accommodate for the demands on both a musculoskeletal level as well as in growing the fetus, says Baird:

  • Musculoskeletally, relaxin helps relax the joints and muscles, including the abdominals, so there is plenty of room for the fetus. 
  • Relaxin also helps relax the blood vessels for increased blood flow (up to 50 percent!) to the fetus.
  • Before delivery, relaxin helps prevent contractions as well as relax the pelvis and cervix leading up to delivery. 
  • Relaxin may even play a role in inducing labor!

Related: Should You Run a Race on Your Period?

When does relaxin hormone start in pregnancy?

Relaxin exists in the body at low levels until ovulation. This is when it starts to rise before falling again. If you become pregnant, relaxin production spikes and peaks in the first trimester.

Relaxin declines for the rest of pregnancy before soaring again just before delivery. Relaxin typically returns to prenatal levels around 5 months, but can remain elevated for up to 24 months postpartum, especially if you are breastfeeding.

Related: 8 Clever Tips for Breastfeeding Mother Runners

How to reduce relaxin postpartum

There is no proven way to reduce relaxin postpartum with the exception of decreasing the time you choose to breastfeed. But runners can reduce the effects of the hormone relaxin and running.

While relaxin may put you at higher risk for injury while running, exercise can help you regain strength which can ward off injury later.

I encourage runners to start with walking (check out my postpartum running plan). This low-impact exercise can help kickstart strengthening your musculoskeletal system to ready your body for running as it heals and the levels of relaxin your body decrease.

Related: Yes! You Can Run with Diastasis Recti!

I also suggest runners work on their core and pelvic floor strength, ideally with a pelvic floor physical therapist, to promote stability and core control.

Finally, if you are feeling unstable as a result of the hormone relaxin when running, wearing a supportive belly band such as the Belly Bandit may help you feel better. (It is important to note that there is no strong evidence that belly binding can help expedite your healing or rehab diastasis recti!).

Related: The Best Belly Bands for Runners

running and relaxin pin 2
Relaxin can put pregnant and postpartum runners at risk for injuries. Pin these tips to stay injury-free.

How does relaxin affect breastfeeding, running

Relaxin plays a vital role in breastfeeding. It works with estrogen and progesterone to develop the breast tissue and its function for nursing. Relaxin is also present in breastmilk, though it’s role is not well-studied.  

This is important to note because if you are breastfeeding—even if your baby is a year old, you still have relaxin in your body and this may increase your injury risk.

Indeed, the hormone relaxin and running can be at odds as it reduces tendon stiffness; loosens ligaments, joints, and muscles which can raise the impact of certain activities like running and put you at a greater risk for falling.

Common injuries and pain related to relaxin include pelvic girdle pain, and pain in your pubic bone, sacroiliac joints, and ankle joints. Studies have shown a relation between an increased risk in ACL tears in females with higher relaxin levels (due to where they were in their menstrual cycle) and a connection to musculoskeletal disease.

While many women won’t notice the impact of relaxin on their running, some may feel unstable or weak. And as Baird puts it, being unstable or weak “can be risk factors for running injury even without the presence of relaxin!”

Thankfully, there are steps you can take to keep running with relaxin.

5 Running tips for relaxin surges

1. Work on your overall strength.

Strength and stability are key factors in preventing injury from running—in all runners no matter if you are pregnant. Pregnant runners should continue strength training with modifications as their pregnancy progresses (see my pregnancy strength training guide here).

A specific focus should be made on core stability and pelvic floor strength and coordination. Core stability will help your balance and pelvic floor and core coordination and strength will help you prepare your body for running injury-free. Working with a pelvic floor physical therapist is the best way to ensure you are addressing your unique strength needs. However, there are many online programs. My favorite that I recommend for my athletes is the ReCORE Fitness Programs. Exercises may include bird dogs, cat cows, and bicycles.

2. Have a solid running plan.

The number one risk factor related to injury is increasing running volume too quickly, notes Baird. And I second that emotion. While you may think you feel normal running during pregnancy or postpartum, your body is undergoing lots of changes including relaxed joints and muscles that can weaken your core, specifically. 

For this reason, working with a running coach such as a myself or following a postpartum running plan while help guide your volume increases so you don’t do too much too soon.

Whatever plan you choose, it should be written in pencil and your body should be your number one guide. Forcing your body to do something before it’s ready will only leave you sidelined.

Related: Is 6 Weeks Too Soon to Start Running Postpartum?

3. Always warm up and cool down.

When you’re pregnant or postpartum, the little things count that much more in keeping you healthy. Therefore, you cannot afford to skip a warm-up or a cool-down. Because relaxin relaxes your joints and muscles, you want to increase blood flow so they are ready for activity.

I suggest doing some dynamic stretches or mobility before walking for about 5 minutes, then easing into your run. When you are done running, walk for about 5 minutes to lower your heart rate. Then do some gentle stretches to help aid in recovery.

4. Run on smooth terrain.

Trail running and relaxin do not go together well. Instead, smooth terrain versus uneven terrain is your best bet. This will minimize the risk of failing, rolling your ankle, twisting your knee, or losing your balance. So, seek roads and paved paths during this time!

5. Have proper footwear.

Your feet likely have grown during your pregnancy so ensure you’re wearing the right size to reduce your risk of falling. You’ll also want shoes that are cushioned and comfortable otherwise you may change your foot strike to reduce pain—and yes, this can lead to falling or injury!

If you can’t find a running shoe you like, go to a running shoe specialty store and have one of their salespeople watch you run and fit you.

Relaxin helps miracles happen–but be wary of its effects!

The hormone relaxin and running can be a match

Relaxin makes the birth of your baby possible! It’s the miracle hormone that allows us to grow and squeeze a whole human out of our bodies! Amazing! But there are some risks when it works this miracle that can make us unstable and injury-prone.

But you maintain your exercise routine! By working with your healthcare provider(s) and your body, you can minimize your risk and stay healthy for you and your baby!

Get more inspiration to run while pregnant »

If you’d like assistance with your postpartum running journey, check out my run coaching services and my other free training plans:


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