Experimental training and educational interventions
POLAND
The HIIT intervention consisted of three 60-min training sessions a week to which women participated for 8 weeks. Participants started with the warm-up combined with short educational guide on how to perform exercises in the main part (this part of the session lasted approx. 7–10 min). The main part lasted approx. 15–20 min and was performed in the form of high intensity intervals. The individual heart rate at anaerobic threshold (HR/AT) was determined for each woman on the basis of the progressive maximal exercise test. The HR/AT was set, on average, at 88 ± 5% of maximal heart rate. With the use of a heart rate monitor (Polar RS400, Finland) women were supposed to exceed the value of HR/AT in workout intervals for as long as they felt comfortable. Additionally, we monitored the exercise intensity with the use of the 0–10 Borg Rating of Perceived Exertion (RPE) and the Talk Test (The workout intervals included exercises that involved the main muscle groups (e.g., squats, lunges, jumps, combined with the upper body movements). They lasted for 30–60 s, alternating with a 30–60 s rest break, in the ratio of exercise time to rest 1:2, 1:1 or 2:1, according to the individual capabilities of the participant and considering the training progression and stage of pregnancy. After the interval part of the training, participants performed resistance, postural, neuromotor (e.g., body balance) and stretching exercises which lasted approx. 5–10 min. The cool down part consisted of pelvic floor muscle exercises and preparation-for-birth exercises, e.g., birth position and breathing exercises (5–10 min) as well as relaxation and visualization of pregnancy and childbirth (5–15 min). Women did not need any equipment during exercises and only resistance of own body was applied. Women were able to participate in the training program regardless of their level of fitness or exercise capacity, as well as the level of motor skills (based on the diagnostic exercise tests, the exercise program was tailored to the individual needs and capabilities of a woman (Group HIIT sessions were provided online, from 9.30 to 10.30 a.m. with the use of the MS TeamsThe control group (EDU group) consisted of 16 pregnant women who participated in educational sessions on a healthy lifestyle, physical activity in the perinatal period and selected aspects of pregnancy and motherhood (this was the same educational program as for the HIIT group). Educational classes were provided online in real time, 1 h once a week for 8 weeks. Women from the EDU group were encouraged to individually undertake exercise and fulfill at least the recommended level of physical activity (minimum 150 min per week of moderate to vigorous intensity). They were asked to keep a diary of all their physical activity (including both structured exercise sessions and daily activities lasting at least 10 min, such as cleaning the house, gardening, shopping). Of note, the EDU group did not monitor the intensity with heart rate monitors, but used the RPE scale and Talk Test. We recommended exercise intensity at a level in which women felt a marked increase in breathing frequency, but until their breathing interfered with their conversation. On average, the participants reported 20 bouts of physical activity with an average intensity of 6 ± 0.6 on the 0–10 RPE scale.During the entire study, all participating women remained under standard obstetric care. Both HIIT as well as EDU interventions were not associated with any negative effects on the course of pregnancy or on childbirth parameters. We collected data on obstetric and neonatal postpartum outcomes, using an online questionnaire (based on medical records).We used the G∗power version 3.1.3. software in order to predetermine sample size (on the basis of the power calculation). The minimal sample size of 32 (16 for each group) with an allocation ratio 1:1, a power of 0.9 and alpha of 0.05 was predetermined on the basis of the values of the mean and SD from preliminary tests with 8 women form the HIIT group and 8 women from the EDU group. The study design is presented on the Schematic representation of the study design. AerT, aerobic threshold; AT, anaerobic threshold; BIA, bioelectrical impedance analysis; CPET, cardiopulmonary exercise test; EDU, education; HIIT, high-intensity interval training; HRThe study was conducted in the Laboratory of Physical Effort and Genetics in Sport, at Gdansk University of Physical Education and Sport in Gdansk, Poland, in 2021. This research was performed according to the principles of the WMA Declaration of Helsinki and with the approval of the Bioethics Commission at the District Medical Chamber in Gdansk (KB-8/21). All participants were asked to sign the informed consent prior testing. The study protocol was registered in 