Running During Pregnancy: Guidance by Trimester

Running during pregnancy is a topic that often causes uncertainty…

Is it safe to run when pregnant?

How long can I continue running?

Are there things I can do to run more safely during pregnancy?

The good news is that in most uncomplicated pregnancies, running can safely continue well into pregnancy if it still feels good and your medical provider has not advised against it. That said, pregnancy does create significant physical and physiological changes that can affect how running feels from trimester to trimester. In this article, we’ll break down the key changes that occur during each trimester along with practical training strategies to help support safer, more comfortable running throughout pregnancy.

Read on to learn:

• General Guidance for Running During Pregnancy
• First Trimester Changes & Training Strategies to Support Running
• Second Trimester Changes & Training Strategies to Support Running
• Third Trimester Changes & Training Strategies to Support Running
• Signs to Regress or Stop Running

Quick Answer: Running during pregnancy is generally safe for those who were already running before becoming pregnant, provided a medical provider has not advised against it. Starting a running program during pregnancy is not recommended. The physical changes pregnancy brings vary by trimester and can significantly affect how running feels, making it important to adapt training strategies as pregnancy progresses. Managing these changes well requires consistent strength training (especially single-leg work), using Rate of Perceived Exertion rather than heart rate to gauge effort, and listening for signs like pelvic pressure, leaking, or labored gait that signal it’s time to scale back or stop.

General Guidance for Running During Pregnancy

If you had been running before pregnancy, it is perfectly safe to continue running during pregnancy – even long-distance running – unless advised to the contrary by your medical provider. If you are feeling good and are not experiencing any of the “signs to stop” (discussed later), you and your baby are capable of managing the stresses of running well into pregnancy.

However, it is not advised to start running during pregnancy. That is because your body needs to be conditioned to handle the impact forces—to minimize the aches and pains that some people experience—during such a dynamic activity.

If you plan to continue running during pregnancy, there are two important things to keep in mind:

1. Strength Training is Critical

Think about this: every time you land on one foot when running, you must absorb roughly 4-6x your body weight. This places a great deal of stress on your soft tissues. As weight gain increases during pregnancy, so too does the force that must be absorbed with each step. In addition, the bigger your body, the more force is needed to propel it forward with each step. The better you can absorb and dissipate impact forces, the less stress running will place on your joints (ankles, knees, hips, lumbar spine) and pelvic floor. Strength training is the means of absorbing force, especially single-leg strength training.

2. Heart Rate is Not a Valid Measurement

Traditionally, heart rate was heralded as a means of gauging exertion during pregnancy, with many doctors using 140 beats per minute as the threshold above which pregnant exercisers should not cross. However, the American College of Obstetricians and Gynecologists (ACOG) – the medical body that provides pregnancy and postpartum exercise guidance in the United States — eliminated heart rate guidance in the 1990s because it was not evidence-based nor specific to each person’s fitness level, degree of exercise experience, age, stage of pregnancy, etc. Today, ACOG advises using Rate of Perceived Exertion (RPE) instead. RPE relies on listening to your body and gauging your exertion by how you feel, which is a more reliable method during pregnancy.

First Trimester Running Guidance

Aside from fatigue or nausea, running may not feel dramatically different during the first trimester because pregnancy weight gain and the resulting alignment shifts have not become major factors yet. However, there are two key things to be aware of in the first trimester.

First Trimester Changes that Impact Running

1. Potential instability: During pregnancy, hormonal changes – including the increase in the hormone relaxin – soften the joints, ligaments, and connective tissue to allow the body to adapt to carry a growing baby and to provide laxity and mobility needed to push a baby out. A consequence of this soft tissue laxity is that it often increases mobility and decreases stability. 
2. Risk of overheating: During the first trimester (especially the first month), it is important to avoid overheating (body temperature above 102° F), as this could interfere with the critical processes of the fetus’s brain and organ development. The pregnant body does adapt to allow greater heat dissipation, but it is important to avoid situations that can make heat dissipation difficult, such as running in high heat and humidity. It is also very important to stay hydrated so your body can continue sweating (which is one of the ways it cools itself).

First Trimester Training Strategies to Support Running

• Assess your stability at rest: To gauge your baseline stability in a single-leg stance, stand on one leg with the opposite knee lifted and note how long and how well you can balance. Also, notice if you can balance better on one leg vs. the other. You can reassess every month or so to determine whether hormonal changes may be affecting your balance. If you feel you need help increasing your stability, check out these 5 moves to build lower body stability.
• Avoid high heat and humidity: Avoid running in high heat and humidity, drink water (before, during, and after running sessions) to enable you to keep sweating, and wear clothing that allows for adequate sweat evaporation.
• Ingrain proper breathing mechanics: Learn how to perform 360° Breathing. This important for several reasons, but specific to running, it improves your cardiac efficiency (delivery of oxygen to working muscles).
• Begin pelvic floor training: Begin early to strengthen your pelvic floor (PF) so that when you gain weight, your PF tissues will be strong enough to continue supporting you. Learn how to do this by practicing Pelvic Floor Activations (PFAs).

Second Trimester Running Guidance

The second trimester is often when running feels better again, especially if first trimester nausea and fatigue have started to subside. There are also a few important changes that may affect your running.

Second Trimester Changes that Impact Running

1. Increased cardiac output: This adaptation may surprise you. During pregnancy, the heart pumps more blood with each beat and beats more times per minute. This confers a cardiac advantage similar to “blood doping,” giving a person increaser aerobic capacity. In fact, there have been cases of athletes setting personal records during pregnancy due to this adaptation!
2. Weight gain: The second trimester is when weight starts to increase. This will likely cause more noticeable changes in your running.
3. Alignment shifts: Compounding the changes caused by weight gain, the growing belly tends to pull the pelvis forward into an anterior pelvic tilt. When we combine this added pressure from the alignment shifts with the added impact of running, it could result in the common pregnancy complaints of low back pain and incontinence (accidental urinary or fecal leakage).

Second Trimester Training Strategies to Support Running

• Take advantage of your “honeymoon” (if it feels ok): The second trimester is often considered the time when you will feel most energetic and motivated to train. Also, remember that you do have the advantage of the increased aerobic capacity. So, if you’re feeling good, you can push yourself if you wish.
• Use Rate of Perceived Exertion (RPE): Knowing the level of intensity to work at can be more challenging during pregnancy because heart rate is no longer an accurate gauge of how hard you are working. Therefore, it is recommended that you use a simple 1 – 10 RPE scale, where 1 = minimal exertion (gentle walking) and 10 = maximal effort (full sprint). Generally, you want to stick to an RPE of 6-8. If you are a more experienced runner, you can push to an 8.5. Remember, RPE is all about how you feel. It will vary highly by individual and also for each individual as pregnancy progresses (and even from day to day). 
• Emphasize neutral alignment: Because greater weight gain and hormonal changes can alter your body position, which could lead to pain in your lower back and hips (among other areas), you want to make sure to maintain neutral alignment as much as possible when running. 
• Focus on lower-body strengthening: As mentioned earlier, strength is critical for absorbing and dissipating impact forces. Therefore, focus your strength training on single-leg moves because running is a single-leg activity.
• Watch for pelvic floor issues: If you experience accidental leakage (urinary or fecal) while running, you may be experiencing pelvic floor dysfunction (PFD). This means there is an imbalance between the loads you are placing on your body and your body’s ability to control them through the pelvis, leading to unintended or spontaneous leakage of urine or feces.
• Use of running “accessories”: As the breasts and belly get bigger, they may become uncomfortable, but they don’t have to curtail your running. Consider doubling your sports bra and possibly using a belly support (NOT a wrap or corset) or high-waisted shorts/tights. We love the pregnancy support products from SRC Health. In addition, changes in your feet may necessitate an increase in shoe size, as hormonal changes, coupled with weight gain, can cause your feet to spread and flatten. This can result in discomfort if your shoes are too tight (or don’t have enough arch support). If you are a more serious runner, you may consider purchasing a larger shoe size (which will likely last you into the postpartum period, as prenatal changes to your feet may become permanent).

Third Trimester Running Guidance

By the third trimester, the changes that began in the second trimester are typically more pronounced. For many people, this is when the body starts signaling that it may be time to lower intensity, reduce mileage, or transition away from running.

Third Trimester Changes that Impact Running

1. Increased Weight Gain and Alignment Shifts: As weight gain increases and alignment continues to shift, running may place more stress on the lower back, hips, knees, ankles, and pelvic floor. For many people, their bodies will tell them they need to lower the intensity and reduce (or stop) running.
2. Altered Running Mechanics: The pelvis widens slightly during pregnancy and, as a result, the feet get wider. This can lead to a change in your stride. Expect a shorter stride with the potential for more side-to-side shifting.
3. Constricted Breathing: As the belly grows, it may push into the chest area, thereby limiting how much the lungs can expand. Therefore, you might find it more difficult to take a deep breath, which may change your breathing pattern and rhythm, making running more difficult.

Third Trimester Training Strategies to Support Running

• Reinforce 360° Breathing: As breathing can become more challenging at this stage, you want to make sure you have mastered 360° Breathing so you know how to expand your ribs three dimensionally when you inhale to maximize air intake. 
• Focus on lower-body strengthening: As mentioned in the second trimester training focus, continue incorporating lower-body moves, especially single-leg work, to maintain your strength.
• Soft tissue care: Doing some foam rolling before running can help keep your tissues supple, especially when you’re loaded with more body weight. Focus on the glutes, hamstrings, hip flexors, and quads.  After running, it’s a good idea to stretch those same areas (and include the calves) to lengthen muscles that became shortened during your session. Note: Just be sure to avoid rolling on or near your belly, or on bulging varicose veins. In third trimester, you also want to avoid rolling on the calf or foot area, as those areas can stimulate contractions.
• Watch for pelvic floor issues: If you experience any symptoms of urinary or fecal leakage during runs, this is a sign that it is best to stop running.
• Routinely “check in”: Above all else, running really comes down to: Does it feel good? If you hesitate when answering that question, then it is probably time to scale back (or eliminate) running and focus on more comfortable movements.

Signs to Regress or Stop Running

• Using the bathroom before or during a running session: If you go to the bathroom preemptively to avoid leaking during running or you have the urge to pee when you are running, you are likely experiencing pelvic floor dysfunction.
• Leaking during the run: A classic sign of pelvic floor dysfunction.
• Labored or loud gait: This typically means that absorbing impact forces is becoming increasingly difficult, leading to less efficient landing mechanics (increasing the impact on your joints and pelvic floor).
• Pelvic pressure: If you are feeling pressure anywhere in the pelvis, the load may be too much for your body to bear comfortably. Rather than continuing to run, which may create discomfort or pain, it is a good indicator that a regression is warranted.
• Not comfortable or fun: Just as you focus on internally-derived measures of intensity, with RPE, seek your own counsel about whether or not you are truly comfortable continuing to run. Whether pride or principle drives you to keep pushing, be gentle with yourself. You want to feel strong and empowered as you get closer to labor.

Ultimately, running during pregnancy comes down to one question: Does it still feel good? Consistent strength training, smart intensity management, and a willingness to scale back when your body signals it’s time are what keep that answer “yes” for as long as possible. Pregnancy changes the body in significant ways, but with the right strategies, you can continue moving safely, effectively, and confidently through each stage.