Ever seen videos of women who are well into their third trimester doing high-intensity interval training (HIIT) workouts? If so, you might be wondering whether this type of exercise training can possibly be safe during pregnancy.

In short: A modified version of a typical HIIT workout — which involves alternating between short bursts of intense activity and less strenuous activity (or "active rest") — can be an efficient way to raise your heart rate and build strength in the busy months before your baby arrives.

Use these tips to stay safe.

Benefits of high-intensity interval training workouts (HIIT)

If you have your doctor's okay — and have modified the exercises properly — HIIT can be great for both mother and baby alike. Here are a few of the benefits:

  1. It can reduce pregnancy aches. If your back and pelvis are strained from carrying around your growing baby belly, strengthening that area may help alleviate pain.
  2. It can relieve constipation. Many pregnant women complain of constipation during pregnancy. But moving your body, even for as little as 10 minutes, can crank up your metabolism, which helps you move your bowels more regularly and effectively.
  3. It reduces fatigue. HIIT builds strength that makes moving much easier — so everyday activities feel less laborious.
  4. It prevents excessive weight gain. While it's healthy to steadily gain weight throughout your pregnancy, exercise can help you fend off excess pounds that make it more difficult to recover your pre-baby body after giving birth. HIIT, in particular, creates an "after-burn," which means it boosts your metabolism to burn extra fat and calories for up to 48 hours after you stop sweating.
  5. It can help alleviate anxiety or stress. Breaking a sweat with HIIT is a welcome distraction that can provide some sweet relief by mustering up exercise-induced endorphins.
  6. It preps your body to give birth. HIIT trains your body to use oxygen more efficiently, which can give you a leg up when it comes time for labor.

Who should — and shouldn't — try HIIT during pregnancy

Wondering if it's okay to keep up your pre-pregnancy fitness routine? Yes, you usually can. Regular exercise doesn't increase the risk of miscarriages, low birth weight and early delivery in women who don't have complicated pregnancies, and research has shown that active women can safely exercise at a vigorous intensity without harming themselves or their babies.

That means if you've regularly trained at a high intensity before you conceived, you may be able to continue a modified version of your regular workout regimen throughout your pregnancy. But as with any exercise you do during pregnancy, you'll want to get your medical practitioner's approval before lacing up your sneakers.

That said, unlike some other fitness routines, HIIT workouts aren't for everyone. You can expect to break a sweat doing HIIT much more quickly than during, say, prenatal yoga or barre. So if you're new to high-intensity training, pregnancy isn't the best time to jump on the bandwagon.

Safety tips for HIIT workouts during pregnancy

As with any workout that you do during pregnancy, you'll want to keep in mind the standard safety rules for exercise during pregnancy, especially:

  • Get your doctor's written approval. In addition to ensuring your workout plan is healthy for your pregnancy, many studios require a doctor's note, so be sure to get your doctor's okay before getting started.
  • Give your teacher a heads-up. Always tell your instructor you're pregnant before taking a HIIT class, and ask if he or she is trained to modify movements for pregnancy. Most are!
  • Avoid certain movements. The American College of Obstetricians and Gynecologists (ACOG) suggests that pregnant women avoid many movements that are typical in HIIT workouts — including jumping, jarring motions or quick changes in direction — since they could strain your joints and increase your risk of injury during pregnancy.
  • Drink up. Keep in mind that even if your instructor doesn't give you designated water breaks, you'll want to sip continuously throughout your workout. It's easy to get overheated when you're pregnant, and dehydration can be dangerous for you and your baby.
  • Catch your breath. You may notice that you're more breathless earlier on in your workout than normal. That's due to various physiological changes in your body from pregnancy hormones — not that you're suddently out of shape! 
  • Listen to your body. To ensure you and your baby are getting plenty of oxygen, keep your effort in check. One way is to use the Borg Scale of Perceived Exertion (a scale ranging from 6 to 20 that measures the intensity of a physical activity, where at 6 you're watching TV and 20 you're going all out). You should keep at around 13 to 14 — where you could keep up a conversation while you work out. The scale also correlates with your heart rate: Multiplying your score by 10 should roughly equal your beats per minute.
  • Tread carefully. Your balance is a bit off when you're expecting, especially later on in pregnancy. So be especially cautious with any exercises where you'll need to balance. Having a wall nearby can be helpful.
  • Don't overstretch. Pregnancy hormones make your muscles, joints and ligaments more flexible than usual in preparation for birth — which means it's important not to push yourself when you stretch to avoid injury.

5 HIIT moves modified for pregnancy

Below is the "full" version of several HIIT exercises, modeled by Dennys Lozada, a trainer at The Fhitting Room, along with the move modified for pregnancy.

If you can, perform each exercise below carefully and continuously for 45 to 60 seconds, resting for 30 to 60 seconds between up to three rounds. Supervision is always ideal for any workout to ensure that your form is correct and you don't overdo it — so don't try these alone.

Once you have your doctor's sign-off, your best bet is to find a studio or gym that offers HIIT classes or to work one-on-one with a personal trainer.

1. Plyo box plank taps (modified plank taps)

For this exercise, position your body so your back is at an incline instead of parallel to the floor. This way, there will be less pressure on your back.

How to do it:

  1. Stand in front of a knee-high box, bench or chair. Place both palms on the surface in front of you and step your feet back until your body is in plank position.
  2. Keeping your body in a straight line from the top of your head to your heels, and your shoulders and hips square to the ground, bring your right hand to your left shoulder.
  3. Replace your right palm and repeat on opposite side, this time bringing your left hand to your right shoulder.
  4. Continue to alternate.

Reps: As many as you can for 45 to 60 seconds

Sets: 1 to 3

2. Reverse lunge-to-bicep curl (modified with lighter weights)

Because you're already carrying the extra weight of your baby belly — which can compromise your balance — modify this move by holding lighter weights.

How to do it:

  1. Grab one 5- to 8-pound dumbbell in each hand and hold them along your sides.
  2. Keeping your elbows close to your sides, curl both weights up toward your shoulders, turning your palms to face your chest as you curl up.
  3. Release the weights back along your sides as you take one large step backward with your left foot and bend both knees 90-degrees, keeping your shoulders stacked over your hips the entire time. Your front knee should be stacked directly over your front ankle.
  4. Return to the standing position and step your left foot up to meet your right foot.
  5. Perform a second dumbbell curl, then a second backward lunge, this time stepping back with your right foot.
  6. Continue alternating between curls and backward lunges, switching sides.

Reps: As many as you can for 45 to 60 seconds

Sets: 1 to 3

3. Body weight step-ups (modified box jumps)

It's not safe to jump onto a box when you're pregnant, especially since your balance is a bit off these days. Instead of jumping onto the box, simply step onto it one foot at a time. Fighting gravity already provides plenty of resistance.

How to do it:

  1. Stand up straight in front of a box or step. Keep the box on the lower side; the higher up it is, the more difficult it will be.
  2. Step up to the box with both feet, leading with your left foot.
  3. Gently step down off the box one foot a time, leading with your left foot.
  4. Repeat, this time leading with your right foot.
  5. Continue alternating your feet.

Reps: As many as you can for 45 to 60 seconds

Sets: 1 to 3

4. Single arm bent-over rows with dumbbell (modified dumbbell plank rows)

Because your baby belly can compromise your balance and put pressure on your lower back, try stabilizing your body weight with your free hand during bent-over rows.

How to do it:

  1. Hold a 5- to 10-pound dumbbell in one hand and take a wide stance in front of a chair or bench, placing your free hand on the surface for support. Bending from the waist, keep a neutral spine as you let the hand holding the dumbbell hang down to the floor, keeping the weight parallel to your body the entire time.
  2. Bend your weight-bearing elbow to bring the dumbbell up along your side. Release with control to complete one rep.

Reps: 10 to 15 reps

Sets: 1 to 3

5. Speed skaters

Placing your back foot down helps you maintain your balance and takes the pressure off of your joints.

How to do it:

  1. Take a large step to the left with your left foot, crossing your right foot diagonally behind your left, and reaching your right hand toward the left foot. Keep the repetitions slow and steady so you don't lose your balance.
  2. Take a large step to the right with the right foot, crossing your left foot diagonally behind your right, reaching your left hand toward your right foot.
  3. Continue alternating feet.

Reps: As many as you can for 45 to 60 seconds

Sets: 1 to 3