Strength Training During Pregnancy: Research, Modifications, and Safety

# Strength Training During Pregnancy: Research, Modifications, and Safety

The outdated advice to rest and minimize activity during pregnancy has been comprehensively updated by modern research. Current guidelines from the American College of Obstetricians and Gynecologists (ACOG), the Society of Obstetricians and Gynaecologists of Canada (SOGC), and other major bodies now recommend regular exercise — including resistance training — during uncomplicated pregnancies.

This article is for general educational purposes. Pregnancy exercise decisions should be made in consultation with your obstetrician or midwife, who can assess your individual circumstances.

What the Research Supports

The research on exercise during pregnancy has shifted significantly. A landmark 2019 systematic review and meta-analysis by Davenport et al. in the *British Journal of Sports Medicine* — analyzing 131 trials including over 11,000 participants — found that exercise during pregnancy was associated with:

• Reduced risk of gestational diabetes (by approximately 38%)
• Reduced risk of gestational hypertension and preeclampsia
• Reduced risk of excessive gestational weight gain
• No increased risk of preterm birth, low birth weight, or adverse neonatal outcomes in uncomplicated pregnancies
• Improved psychological well-being and reduced depression symptoms
• Reduced pregnancy-related low back and pelvic girdle pain
• Shorter active labor in some studies

The same review supported resistance training as a safe modality during uncomplicated pregnancy, noting similar risk profiles to aerobic exercise when performed within appropriate guidelines.

Research by Barakat and colleagues, who have published extensively on resistance training and pregnancy, found that supervised resistance training programs throughout pregnancy did not adversely affect fetal or maternal outcomes in healthy, low-risk pregnancies, while producing benefits for weight management and physical function.

Exercise Recommendations by Trimester

First Trimester (Weeks 1–12)

Physiologically, the first trimester involves the least structural change to the body. For women who were already training, continuing their existing program with few or no modifications is generally appropriate, subject to how they feel (nausea, fatigue, and energy availability are highly variable in the first trimester).

Women new to exercise can typically begin a moderate-intensity resistance training program in the first trimester with clearance from their healthcare provider.

Key considerations:

• Hydration and avoiding overheating are important throughout pregnancy — elevated core body temperature is a concern
• Nausea may affect tolerance for certain exercises and nutrition timing
• Existing cardiovascular adaptations mean that perceived effort is a more reliable guide than heart rate percentages

Second Trimester (Weeks 13–27)

Many women experience improved energy in the second trimester. The growing uterus begins to affect balance and center of gravity, and some modifications become appropriate:

Position modifications: The ACOG advises avoiding exercises performed lying flat on the back (supine) for extended periods from around 20 weeks onward. This guidance relates to potential compression of the inferior vena cava by the uterus, which can reduce venous return. For most exercises, slight lateral tilt (using a wedge or incline) or transitioning to seated, standing, or supported positions resolves this concern.

Affected exercises and alternatives:

• Bench press → incline bench press, dumbbell press on a 15–30 degree incline, or standing cable press
• Floor-based core work → inclined or standing core work
• Supine ab exercises → standing core stability, Pallof press, bird dog

Load selection: Continue progressive resistance training, but recognize that absolute loads may need to decrease as the center of gravity shifts and balance is affected. Training with a qualified personal trainer experienced in prenatal exercise is valuable during this period.

Third Trimester (Weeks 28–40)

The third trimester brings increasing physical demands: greater body weight, more pronounced center of gravity shift, joint laxity from relaxin, potential pubic symphysis discomfort, and decreased exercise tolerance. Training should be modified more significantly:

• Focus on functional movements that support labor preparation and postpartum recovery
• Reduce load and emphasize technique and control
• Pelvic floor work becomes particularly important
• Avoid high-impact movements and activities with fall risk
• Listen carefully to symptoms: shortness of breath, dizziness, pelvic pressure, or contractions warrant stopping activity and consulting a healthcare provider
• Squatting (supported if necessary) may be limited by pelvic girdle pain — machine leg press or seated variations may be more comfortable

Specific Considerations for Strength Athletes

For women who were strength training seriously before pregnancy, several specific considerations arise:

Intra-abdominal pressure: Heavy compound lifts (deadlifts, squats, heavy pressing) generate significant IAP. While moderate IAP is generally safe, very heavy valsalva-intensive loading carries theoretical concerns for the pelvic floor, particularly as pregnancy progresses. Many prenatal fitness professionals recommend avoiding maximal effort and valsalva-intensive loading, particularly in the third trimester, though the research specifically addressing this in strength athletes is limited.

Diastasis recti: Abdominal separation (diastasis recti) occurs to some degree in most pregnancies as the linea alba stretches. Exercises that create significant outward pressure on the abdominal wall (heavy loaded sit-ups, certain core exercises) are typically modified or avoided. A women's health physiotherapist can assess and guide individualized modification.

Relaxin and joint laxity: The hormone relaxin, produced from early pregnancy, increases throughout the first and second trimesters and increases joint laxity — particularly in the pelvic girdle but systemically as well. This increases the theoretical risk of joint injury with very heavy loading and poor technique. Careful attention to mechanics and avoiding end-range loading under heavy loads is warranted.

Pelvic girdle and pubic symphysis pain: A common and limiting complaint in pregnancy. Heavy squats, wide-stance work, and single-leg movements can aggravate this condition. Switching to a narrower stance, reducing range, or transitioning to supported bilateral movements may be necessary.

Absolute Contraindications to Exercise in Pregnancy

ACOG lists several contraindications where exercise should not be undertaken without medical clearance or at all:

• Hemodynamically significant heart disease
• Restrictive lung disease
• Incompetent cervix/cerclage
• Multiple gestation at risk for premature labor
• Persistent second- or third-trimester bleeding
• Placenta previa after 26 weeks of gestation
• Premature labor
• Ruptured membranes
• Preeclampsia/pregnancy-induced hypertension

Any high-risk pregnancy classification, or conditions identified in prenatal care, require physician guidance before continuing an exercise program.

Warning Signs to Stop Exercise Immediately

Stop exercising and contact your healthcare provider if you experience:

• Vaginal bleeding
• Abdominal pain or contractions
• Amniotic fluid leakage
• Dyspnea (difficulty breathing) before exertion
• Dizziness or feeling faint
• Chest pain
• Headache
• Muscle weakness affecting balance
• Calf pain or swelling (possible DVT)

The Bottom Line

For healthy women with uncomplicated pregnancies who were already strength training, continuing a modified program throughout pregnancy is supported by evidence and recommended by major healthcare bodies. For women new to resistance training, beginning a supervised, moderate program during pregnancy is appropriate with medical clearance.

The modifications described above are not restrictions on what women can achieve — they are a framework for training intelligently through a physiologically dynamic period. The strength and body awareness built through pregnancy-appropriate training can substantially support labor, postpartum recovery, and long-term health.

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*This article is for informational purposes only. Always consult your obstetrician, midwife, or healthcare provider before beginning, continuing, or modifying an exercise program during pregnancy.*