Stress is not so bad-cortisol level and psychological functioning after 8-week HIIT program during pregnancy: a randomized controlled trial
Question
What is the impact of an 8-week pregnancy-adapted HIIT program on hair cortisol levels, and are hair cortisol levels associated with depressive symptoms, fear of childbirth, mental and physical health, physical activity, or exercise capacity in pregnant women?
Summary
This randomized trial compared an 8-week supervised HIIT program with an 8-week educational program in pregnant women with uncomplicated singleton pregnancies. Hair cortisol increased in the HIIT group and decreased in the education group, but cortisol changes were not associated with depressive symptoms, physical or mental health, fear of childbirth, physical activity, or VO2max. Mental health improved in the HIIT group, while fear of childbirth decreased significantly in the education group.
Methodology
- 38 Caucasian women in uncomplicated singleton pregnancy; 22 completed/analyzed in HIIT and 16 in education comparison.
- 38 participants.
- Bodyweight major-muscle-group intervals plus resistance, postural, neuromotor, stretching, pelvic floor, birth-preparation, breathing, relaxation, and visualization exercises.
- Work intervals: 30-60 seconds.
- Recovery: 30-60 seconds.
- Intensity: Exceed individual HR/AT for as long as comfortable; HR/AT averaged 88 +/- 5% HRmax; monitored by heart rate, Borg RPE, and talk test.
- 60 minutes.
- 3 sessions/week.
- 8 weeks.
- Randomized controlled trial using pipeline arm-focused randomization; pre-post assessments before and after 8 weeks.
- Hair cortisol, Depressive symptoms, Fear of childbirth, and Health-related quality of life were tracked.
Outcomes
Hair cortisol
Hair cortisol increased in the HIIT group from 13.26 +/- 18.10 to 17.2 +/- 8.36 pg/mg and decreased in EDU from 17.80 +/- 9.92 to 10.7 +/- 6.90 pg/mg.
Between-group Time 2 t = 2.514, p = 0.017, d = 0.826; within HIIT Z = -1.964, p = 0.05; within EDU t = 2.017, p = 0.044.
Mental health
Mental health improved significantly within the HIIT group and did not significantly change in EDU.
HIIT t = -2.125, p = 0.046, d = -0.453; EDU t = 0.154, p = 0.879.
Fear of childbirth
Fear of childbirth decreased significantly in EDU but not significantly in HIIT.
EDU t = 2.444, p = 0.027, d = 0.611; HIIT t = 0.460, p = 0.650.
VO2max
VO2max was maintained in HIIT but decreased significantly in EDU, producing a significant between-group difference at Time 2.
Time 2 t = 2.785, p = 0.008, d = 0.915; EDU within-group t = 4.903, p < 0.001.
Cortisol correlations
Hair cortisol and changes in hair cortisol were not significantly correlated with depression symptoms, physical or mental health, fear of childbirth, physical activity, or VO2max.
All reported Pearson correlations in Tables 3 and 4 were nonsignificant.
Insights
- Pregnancy HIIT evidence must be framed around cleared, uncomplicated pregnancies and adapted supervision.
- For safety-sensitive populations, interval intensity can be threshold-based and comfort-limited rather than all-out.
- A rise in cortisol after HIIT should not be automatically translated into harmful stress without concurrent psychological or clinical outcomes.
Limitations
- Small analyzed sample.
- Special population: uncomplicated pregnant women only.
- Baseline hair cortisol and mental health differed between groups.
- No detailed session attendance, achieved intensity, adverse-event, or postpartum follow-up data.
- Hair cortisol analysis excluded participants with recent hair dyeing.
- Sleep quality was not specifically measured.
Safety
- No specific adverse events or injuries were reported.
- Participants required obstetric clearance and absence of contraindications to increased physical effort.
- The authors state that HIIT cortisol increases were not linked to negative psychological or psychophysical outcomes.