Endurance Sports During Pregnancy: Training Adjustments for Triathletes

The Medical Consensus on Exercise During Pregnancy

The ACOG (American College of Obstetricians and Gynecologists) 2020 guidelines clearly state:

• Women with uncomplicated pregnancies should exercise regularly
• Moderate-intensity aerobic exercise for 150 minutes/week is the baseline
• Resistance training, yoga, and swimming are all encouraged
• “Guidelines designed for athletes” were also incorporated into the update

But pregnancy management for endurance athletes requires more nuance.

Physiological Changes Across the Three Trimesters

Heart Rate Is No Longer a Good Indicator

The traditional “pregnancy heart rate cap of 140” has been abandoned. The reasons are:

• Increased blood volume → heart rate is 10–20 bpm higher at the same intensity
• Individual variation is enormous
• Cardiorespiratory adaptations mean elite athletes naturally have lower RPE

New Standard: Rating of Perceived Exertion (RPE)

• Target RPE 6–7/10 (able to speak in full sentences)
• “Talk Test”: able to hold a conversation but not sing
• Use RPE as the primary monitoring tool instead of heart rate

Adjustments for Each of the Three Disciplines

Running

• Can continue in the first trimester but reduce volume
• Second trimester: many begin to experience pelvic discomfort and need a pelvic support belt
• Third trimester: most switch to walking + aqua running
• Avoid: high-intensity intervals, long downhill descents, high-impact trail running

Cycling

• Indoor triathlon bikes are safest (no risk of falling)
• Second trimester posture adjustments: raise handlebars, change saddle position
• Third trimester: switch to indoor stationary bikes or recumbent bikes
• Avoid: outdoor road cycling (especially for beginners), mountain biking, mass-start races

Swimming: The Queen of Pregnancy Exercise

• Buoyancy reduces joint load
• Excellent heat dissipation
• Full-body exercise
• Can continue until one week before delivery
• Avoid: diving, deep diving, overheated pools (>32°C)

Red Flag Signs Requiring Immediate Cessation of Exercise

Stop immediately and seek medical attention if any of the following occur:

• Vaginal bleeding or amniotic fluid leakage
• Regular uterine contractions
• Persistent headache, visual disturbances
• Chest pain, severe shortness of breath
• Unilateral calf swelling and pain (warning sign of blood clot)
• Decreased fetal movement
• Severe dizziness or fainting

Temperature Management: Core Guidelines

• Core body temperature must not exceed 39°C
• Indoor exercise: avoid high heat and humidity, pay attention to heat dissipation
• Saunas and hot baths are prohibited
• The first trimester is most critical (neural tube development)
• Hydration: increase intake by an additional 300–500 ml/day compared to pre-pregnancy

Resistance Training Adapted for Pregnancy

Benefits:

• Prevents lower back pain and pelvic pain
• Maintains a foundation for postpartum recovery
• Improves insulin sensitivity
• Reduces the risk of gestational diabetes

Adjustments:

• First trimester: can maintain original intensity, avoid breath-holding
• Second trimester: switch to machines, reduce weight, increase repetitions (12–15 reps)
• Third trimester: avoid supine positions (compression of major vessels when lying on the back)
• Completely avoid: Valsalva maneuvers, box jumps, unstable single-leg movements

Weight Management

For women with a normal BMI, the recommended gestational weight gain is 11.5–16 kg. Athletes tend to gain weight at the lower end of the range, but don’t aim for “no weight gain”—the fetus, placenta, amniotic fluid, and increased blood volume alone account for 7–8 kg.

The Psychological Aspect

Many female athletes experience the following during pregnancy:

• Anxiety about losing their identity
• Discomfort with body changes
• Worry about returning to performance
• A sense of isolation from training peers

Recommendation: Seek out an OB-GYN or sports psychologist who has worked with athletes, and join pregnancy exercise communities (such as The Performance Doula).

A Shift in Perspective

Pregnancy is not a “training pause,” but rather a “change in training goals”—shifting from performance enhancement to building reserves for postpartum recovery. View these 40 weeks as an “investment in becoming a stronger mother-athlete after delivery.”

Related Reading

• Endurance Exercise During Pregnancy: A Safety Framework for Intensity, Temperature, and Maternal Hemodynamics
• Prenatal and Postpartum Endurance Training: Safety Boundaries and Return-to-Sport Timeline
• Exercise During Pregnancy and Postpartum Return: A Complete Guide for Endurance Athletes
• Exercise and Pregnancy: A Safety Guide for Exercising While Pregnant—A Comprehensive Analysis from Coaching and Sports Science Perspectives