Overview

Research has firmly established that strength and resistance training benefits physical and mental health. Lifting weights may be the first thing that comes to mind when thinking about strength training. This can include resistance bands, kettlebells, and body-weight exercises like pushups, pull-ups, or squats. Even activities like plyometrics and yoga can be considered strength training. Although there is a lot of research on exercise during pregnancy, there are limited studies on strength training. ACOG attributes the lack of literature to resistance training not being considered a safe activity in early guidelines for exercise during pregnancy. This was due to potential injury and possible fetal heart decelerations. This episode examines the evidence on strength training, physical changes that can affect strength training, and precautions and tips to make your workouts safe during pregnancy.

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Exercise in Pregnancy

There is a separate episode with an overview of exercise during pregnancy. This includes general recommendations and safety tips to keep your workouts healthy for you and your baby. Plus, a breakdown of the physical changes and common pregnancy symptoms that can affect your workouts. I recommend you listen to the episode on Exercise in Pregnancy before diving into this article on strength training.

What is Strength Training

Strength training is a form of exercise that increases your muscle strength. We often think about lifting weights as strength training, but this can also include using resistance bands, kettlebells, and body-weight exercises like pushups, pull-ups, or squats. Even exercises like plyometrics and yoga can be considered strength training.

Benefits of Strength Training

There is a lot of evidence on the benefits of strength and resistance training for both your physical and mental health. Strength training positively benefits your metabolism, reduces fat, improves physical performance, improves insulin sensitivity, reduces risks for diabetes, and promotes bone development and density. Plus, strength training can decrease symptoms of depression, increase self-esteem, and even improve cognitive ability. Strength training is even more critical as we age. Muscle mass decreases 3-8% every decade starting in your thirties. After age 50, muscle loss increases to 5-10% per year. This decrease in muscle is accompanied by a resting metabolic rate reduction and fat accumulation.

One study found that strength training in pregnancy decreased fatigue and increased physical and mental energy. A systematic review of 61 randomized controlled trials examined different types of exercise and their effects on maternal health. The researchers found the exercise modality that seems to induce a more favorable effect on maternal health is the combination of aerobic and resistance exercises.

Recommendations for Strength Training

Even the American College of Obstetricians and Gynecologists recognizes that there “is sparse literature on this topic.” ACOG attributes the lack of literature to resistance training not being considered a safe activity in early guidelines for exercise during pregnancy. This was due to potential injury and possible fetal heart decelerations.

The Research on Strength Training During Pregnancy

While there is a lot of research on exercise during pregnancy, few studies specifically examine strength training. A small study showed that low-to-moderate strength training is safe during pregnancy. In this study, the training included a 45-minute session of 5 exercises with two sets of 15 reps each. The exercises were all on machines and included leg extension, leg press, arm lat pull-down, leg curls, and a lumbar extension. A study with 160 women found that light-intensity resistance training and toning exercises performed over the second and third trimesters of pregnancy do not have a negative impact on the newborn’s body size or overall health.

A study of 92 women found moderate to vigorous resistance exercise safe in pregnancy. This study used a modified version of BODYPUMP workouts, which used high repetitions of lightweight barbells. Sessions were one hour, including warm-up and wind-down. To modify the workouts for pregnancy, squat jumps were exchanged for heel raises, the squats were less deep, and the abdominal training was exchanged for pelvic-lift and static-abdominal training. It is essential to keep in mind that you can modify any exercise for pregnancy.

Lifting Heavy Things

ACOG addresses lifting in relation to occupational considerations during pregnancy if you work in a job requiring you to lift items. ACOG states that lifting, in particular, poses a risk of musculoskeletal injury and low back pain. The National Institute of Occupational Safety and Health recommends limits for lifting in the workplace and has recommendations specifically for pregnant workers. The limits vary based on where you are in your pregnancy, the height of the lift, the distance from your body the item is, and how often you are lifting. The weight limits are relatively low, especially for lifting from below your waist.

It really doesn’t work to extrapolate these guidelines to weight lifting or strength training. Lifting a heavy box that you have to hold away from your body differs from lifting weight like a dumbbell, kettlebell, or resistance bands.

Physical Changes That Can Impact You When Strength Training

Let’s review how some physical changes during pregnancy could affect strength training.

Relaxin

Your ligaments are the connective tissues that help keep bones, joints, and organs in place. If you stretch a ligament too far or tear it, the resulting injury is a sprain. During pregnancy, a hormone called relaxin relaxes your ligaments. This is good to allow your pelvis to expand during birth. The downside is that it can also loosen other ligaments, putting you at a higher risk of injury. If your ligaments are looser, you have less stability in your joints, and it is easier to overstretch your ligaments, which can cause pain or injury.

Your Growing Belly

Your growing belly may also present some challenges for strength training. As your uterus grows, it puts more pressure on your vena cava. Your vena cava is the main artery that carries unoxygenated blood from the lower half of your body back to your heart. If there is a lot of pressure on this vein, it could decrease the flow of blood, which could ultimately reduce your oxygen and oxygen getting to your baby. This concern has been raised concerning sleeping on your back. What about exercises or strength training while lying on your back?

A systematic review to determine whether prenatal supine exercise is associated with adverse outcomes found that although many countries caution against supine exercise after 16 weeks, these recommendations are primarily based on expert opinion rather than explicit scientific evidence. Overall, the researchers concluded that supine exercise is not associated with adverse pregnancy outcomes. There is insufficient evidence to determine whether exercise in the supine position is safe or should be avoided during pregnancy.

There is a difference between spending several hours on your back and lying on your back for a few minutes to complete an exercise. You can also modify some positions to be in more of an incline position rather than flat on your back. Or, if you are planning several exercises or reps in a supine position, mix up your routine to alternate positions, so you have breaks between sets that require you to be on your back.

Your growing belly may also limit what machines or positions you can be in since it will be uncomfortable to lie on your belly or have your belly resting against the machine. If you are doing pushups, you don’t want to start lying on your belly, and you may not be able to go all the way to the ground to avoid putting pressure on your belly. If you are lifting weights in front of you, be careful when holding weight further away from your body since you are at a higher risk for injury. Your growing belly can also throw off your center of gravity.

Valsalva Maneuver

In the past, doctors thought that the Valsalva maneuver during pregnancy reduced blood and oxygen flow to your baby. This is one of the reasons doctors advised against strength training during pregnancy. The Valsalva maneuver is a breathing technique used when lifting heavy weights. Generally, you take a deep breath with your belly before the rep, and then during the most strenuous part of the rep, you exhale with your glottis closed so that no air escapes. Your glottis is a structure in your windpipe that allows air in and out. Then, you exhale after the most strenuous part of the lift. This breathing technique creates pressure in your abdominal and thoracic cavities, which reduces the load on your spine.

More recent research using a 3-D Doppler ultrasound shows that placental blood flow does not decrease during the Valsalva maneuver. Hopefully, we will see more research in the future focusing on strength training during pregnancy.

Experience Level Matters

There is a difference between someone training for a long time and someone just starting to incorporate weights or strength training into their exercise. Your experience and comfort level with strength training will affect how comfortable you are continuing these exercises during your pregnancy.

Regardless of whether you are pregnant, it is essential to take precautions to make sure you are using weights, bands, or machines correctly. There are a lot of resources you can utilize to learn aspects of weight lifting and safe training. The best resource is someone teaching you about techniques in person. This could be a personal trainer, an instructor at your gym, or a friend knowledgeable about strength training. Many gyms have classes with an instructor available to assist with technique. Classes tend to be more cost-effective than personal training. If you can work with someone with experience with strength training for clients during pregnancy, that is ideal.

Warning Signs

Most of the warning signs that indicate you should stop exercising are obvious. The list from ACOG includes regular, painful contractions of the uterus, bleeding, fluid gushing, or leaking from the vagina. Other warning signs include feeling dizzy or faint, shortness of breath before exercise, chest pain, headache, muscle weakness, calf pain, or swelling. Paying attention to your body and how you feel is the key to keeping your workouts and strength training within safe limits. You may also need to modify your training as your pregnancy progresses. Listen to your body, and if you feel like you may be overdoing it, you probably are.

Tips for Strength Training

You can do many things to make strength training exercises as safe as possible. Proper techniques will maximize the results for the muscles you work on and help prevent injuries. If you are not confident in your ability to perform an exercise, don’t do it or get instruction from someone knowledgeable.

Squats are a fantastic exercise during pregnancy. The more squats you do, the longer you will be comfortable in a squat position during labor. There is evidence that being in an upright position, especially in a squat, is beneficial during labor and may even reduce labor length.

Remember that you can always modify any exercise. You may want to try switching out free weights for bands. You can always decrease your weight and increase repetitions.

Talk to Your Doctor or Midwife

You should discuss your exercise and activity with your doctor or midwife in the context of your level of experience and the particulars of your pregnancy. If your care provider has reservations about strength training exercises you feel comfortable doing, please talk through their concerns. If you are new to strength training, working with an expert who can assist you with proper techniques is invaluable. Whether you are an avid weight lifter or just starting, you can modify almost any strength training activity to feel empowered to train during pregnancy safely.

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