There is a persistent old-school narrative that pregnancy is a time strictly for resting, scaling back, and maintaining the status quo. That was especially for individuals who weren’t already regularly exercising beforehand.
However, a new study by Clifton J. Holmes et al. (2026), highlighted by the Lion Health Lab and Brianna Battles, challenges that narrative head-on.
The study dives into a specific question: What happens when previously sedentary pregnant women with obesity embark on a structured, supervised exercise program?
Here is a look at the study design, what researchers found, and what coaches and athletes should take away from it.
Who Participated and What Did Training Look Like?
To find out how exercise impacts maternal health and birth outcomes, researchers randomly assigned 264 pregnant women with obesity who were previously sedentary into one of two groups: standard prenatal care or standard care plus structured exercise.
All participants had singleton pregnancies (a single baby, not twins or triplets, etc) and received explicit healthcare-provider clearance to exercise.
For the intervention group, training kicked off around 14 weeks of pregnancy on average. The structure consisted of three sessions per week, lasting 30 to 45 minutes each. Over the first six weeks, sessions progressed toward 30 minutes of aerobic exercise, 10 minutes of resistance exercise, and 5 minutes of stretching.
Crucially, this was not a heavy-lifting or high-intensity program. Instead, participants utilized resistance machines for movements like leg presses, leg curls, chest presses, shoulder presses, rows, and pulldowns. Training was individualized and kept to a low-to-moderate intensity, targeting no higher than 14 on the 6 through 20 rating of perceived exertion scale.
The Findings: They Could Do More Work at a Similar Effort
The core finding of the study centers on cardiorespiratory fitness and functional capacity. Between approximately 12 and 24 weeks of pregnancy, the results showed a clear divergence between the two groups.
The exercise group saw their average treadmill workload increase by about 15 watts, whereas the standard-care group saw their average workload decrease by about 6 watts.
Both groups were assessed at a similar perceived effort. Being able to handle a higher workload at the same perceived exertion means these previously sedentary women genuinely improved their fitness through mid-pregnancy.
It is worth noting where things did not change drastically. Researchers did not detect significant intervention effects regarding pregnancy weight gain, blood pressure, inflammatory markers, depression and stress scores, birth weight, or delivery method.
The standout, clearest benefit was cardiorespiratory fitness. Additionally, no adverse events occurred during or immediately following the training sessions.
Key Takeaways for Coaches and Athletes
If you are an athlete, coach, or someone navigating pregnancy yourself, what should you glean from the study?
First, starting point matters. These participants were entirely inactive prior to the study, meaning results and baselines for seasoned, trained athletes may look entirely different.
Second, the program matters. This study tested a specific blend of moderate aerobic work and machine-based resistance training rather than heavy lifting or high-intensity sport.
Finally, participation and attendance changed. Attendance declined later in pregnancy, showing that a sustainable program needs room to adapt to the physical realities of advancing gestation.
Ultimately, pregnancy does not automatically rule out building fitness.
In this study, previously sedentary women successfully improved their exercise capacity through mid-pregnancy without adverse events, demonstrating that beginning or maintaining training can be a meaningful part of the pregnancy journey.
