# Stress is not so bad-cortisol level and psychological functioning after 8-week HIIT program during pregnancy: a randomized controlled trial PMID: 38259751 Journal: Frontiers in public health Published: 2024-01-08 Authors: Wilczyńska D, Walczak-Kozłowska T, Santos-Rocha R, Laskowski R, Szumilewicz A ## 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. ## Population - 38 Caucasian women in uncomplicated singleton pregnancy; 22 completed/analyzed in HIIT and 16 in education comparison. - Sample size: 38 - Age: HIIT 30.18 +/- 4.21 years; EDU 32.38 +/- 3.52 years - Sex: Pregnant women - Fitness level: Initial VO2max around 24-25 ml/kg/min; weekly physical activity around 2700-2800 MET-min/week. - Health status: Uncomplicated singleton pregnancy, cleared for adapted physical activity. ## Methodology - Randomized controlled trial using pipeline arm-focused randomization; pre-post assessments before and after 8 weeks. - 8 weeks - Online supervised pregnancy exercise intervention and educational comparison program; recruitment by mass media invitation in Poland. - Randomized and controlled study design. ## Protocol - Pregnancy-adapted supervised HIIT. - Modality: 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. - Session duration: 60 minutes. - Frequency: 3 sessions/week. - Program length: 8 weeks. - Progression: Work-rest ratio and intervals individualized by capability, training progression, and pregnancy stage. - Educational program. - Modality: Education on healthy lifestyle and physical activity in the perinatal period; standard moderate-intensity physical activity described by authors. - Intensity: Standard moderate-intensity physical activity. - Program length: 8 weeks. ## Outcomes ### Hair cortisol Status: mixed 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 Status: improved 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 Status: mixed 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 Status: mixed 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 Status: no clear change 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. ## Practical 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 And Adherence - 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. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/38259751/) (pubmed) - [DOI](https://doi.org/10.3389/fpubh.2023.1307998) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10800893/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.