The present protocol aims to evaluate the effect of two different 16-week High-intensity interval training (HIIT) programs on daily physical activity, body composition, cardiorespiratory fitness, eating behaviour, enjoyment and quality of life in overweight women. Methods: Ninety overweight women (25 - 50 years old) with a body mass index ≥ 25 kg/m2 will be randomly assigned to three groups of 30 participants: a remote home-based HIIT intervention group; a traditional HIIT intervention group; and a non-exercise control group. Both intervention groups will undergo a 16-week progressive HIIT program following the Tabata method. Participants will be assessed at baseline, 4th, 8th, and after 16-week for physical activity, body composition, cardiorespiratory fitness, eating behaviour, enjoyment and quality of life. The study will have a 16-week follow-up post intervention. Results: The participant's enrolment will begin in December 2021, and investigators will anticipate the study completion by the mid of 2022. Conclusions: The HIIT programs might have beneficial effects on daily physical activity, body composition, cardiorespiratory fitness and overall quality of life in overweight women. Moreover, it might be a more enjoyable form of exercise, once it is performed faster than other exercise forms. As a beneficial side effect, these healthy behaviours might have a favourable impact on women's eating behaviours. This study results are expected to add health and well-being professionals' evidence-based knowledge to create strategies and design home-based exercise interventions.

Methods Trial design: The study will be a 3-arm Randomized Controlled Trial, in which a similar number of participants will be assigned to three groups: a supervised remote home-based HIIT intervention group (Home-HITT), or a presential a supervised traditional HIIT intervention group (Traditional-HIIT), and a non-exercise control group (CG). The study will have a 32-week duration and will be carried out in Portugal. This RCT will be "single-blind".

This study has been designed according to CONSORT statement for clinical trials. This RCT will apply the "intention-to-treat principle".

Dose rationale: The CG participants will maintain their usual physical and dietary activity. Nevertheless, after the 16-week intervention, participants selected to the CG will have the chance to receive the same 16-week HIIT program. Both interventions will consist of a 16-week exercise program with HIIT with a frequency of 3 days/week. The Home-HIIT group participants will attend HIIT workout sessions supervised by a specialised instructor via a videoconference application, while the Traditional-HIIT group participants will attend HIIT workout sessions supervised in person by the same instructor. Every HIIT workout session will have a 10 minutes' warm-up, followed by an 8/12/16/20 minutes of HIIT training and 5 minutes' cool-down. The intervention will have a type of HIIT program called the Tabata method once it can be performed in home-based programs. Tabata training method has been defined as a HIIT with submaximal effort performed at 80-95% of maximal heart rate.

Tabata method uses eight sets of 20 seconds of exercise bouts separated by 10 seconds rest, in 2 to 5 blocks. It seems that this method is demanding for ordinary adults so it will have four stages of physical adaptation.

Before each session, all participants in the intervention groups will receive a class reminder through a short message service (SMS). After each session, all participants will also receive an SMS with positive reinforcement about their exercise session participation. In order to compensate for possible absences, extra classes will be given. The 16 weeks intervention period was chosen because evidence shows that this period is sufficient to evidence changes in PA levels. Guidelines suggest the need to accumulate 75 min/week of vigorous-intensity PA. Despite the guidelines, this exercise protocol will be characterized by progression in both exercise intensity and volume because the investigators will be handling sedentary and overweight women.

The present study will have a follow-up period of 16 weeks. During this period, it is necessary to verify the study variables' evolution.

Selection and Withdrawal of Subjects: Participants in this study will be volunteers recruited through Health Centers Portimão, Lagoa and Lagos (Algarve, Portugal) and through promotional flyers placed in region´s local councils. All the participants will be informed of the procedures of the study before signing the informed consent form.

Subject Withdrawal: Individuals will be removed from the study when the following situations are verified: i) medical indication; ii) prolonged illness during the study or injury incapacitating to continue the study; iii) show willingness to leave the study. Participants may be replaced if the withdrawal happens before the intervention starts.

Discontinuation: The study should be interrupted if it is found that the application of the HIIT exercise program is at the origin of the participants physical and/or psychological problems. There will also be an interruption of the study if it is found that the participant initiated a physical exercise program parallel to the study.

Sample size Determination: To determine a priori the sample size, investigators used G*Power (version 3.1.9.7). The sample size was determined by the study's primary objective (effect of the intervention on PA, body composition and cardiovascular health). Based on a large effect size of 0.80 (Cohen's f), performing a sample size calculation for repeated measures analysis of variance with an expectable correlation of 0.50 between measurements, alfa of 0.05 and 85% of power, a total sample size of 60 women will be needed.

Once the investigators have two experimental groups, the aim is to have 90 women in this study.

Statistical Analysis SPSS (StatisticalPackage for the SocialSciences) software, version 27.0, IBM Windows will be used.

Regarding the procedures for sample distribution characterization's, the mean, standard deviation and amplitude of the distribution (min. value and max. value) will be determined. To determine data normality, the investigators will use the Kolmogorov-Smirnov analysis. Parametric statistics will be applied if data is normally distributed. One-way ANOVA will be used for comparisons of the three groups on all outcome's variables. To determine the relation between the independent measures, the investigators will use a two-way ANOVA. If there are significant differences between the different groups, the Bonferroni Post-hoc test will determine significance levels. In this study, the investigators will use a p-value of 0.05.

Randomization: In order to minimize selection bias, stratified randomization will be carried out when allocating individuals to the experimental and control groups, thus maintaining identical characteristics in both groups This stratification will be carried out based on age, sex and ethnicity.

Instruments: For the present study, participants will be evaluated before the intervention in the 4th ,8th and 16th week of the intervention. After that, participants will be evaluated in the 32nd week for follow-up to analyse the possible effect of detraining. Assessments will be performed through the following instruments:

1. Sociodemographic questionnaire - Questionnaire made for the study with questions about age, sex;
2. Anthropometry and Body Composition - Stature and weight will be evaluated to calculate body mass index. Weight and statures will be measured to the nearest 0.1Kg and 0.1cm correspondingly (calibrated weighing-machine and stadiometer). For the body mass index calculation, weight in kilo-grams will be divided by the height in squared meters. The criteria for defining excess weight and obesity proposed by World Health Organization. The waist circumference will be recorded using a non-elastic measuring tape, which is placed horizontally above the top of the iliac crest. This measurement should be performed with a tense tape without compressing the skin and at the end of exhalation. It will be assessed % fat mass, bone mass and muscle mass with a bioimpedance weighing-machine electric model Tanita BC601. Before the test, the participants will be told to lie down in a supination position to ensure good blood circulation;
3. Blood Pressure (BP) - The BP will be assessed using electronic BP device OMRON M2 (13) according to validation protocols;
4. PA Questionnaire - For measuring PA, by questionnaire it will be used International Physical Activity Questionnaire - Long Version (IPAQ);
5. Daily PA - Objectively measured daily PA will be assessed through accelerometers, using the Model ActiGraph GT3X+ (Pensacola, USA), triaxial accelerometer, supported by the ActiLife Software. ActiGraf models have been widely used in research, and it is estimated that more than 50% of the research using accelerometry uses this brand. Participants will use the accelerometer for seven consecutive days, during the day and night (night sleep), except for activity involving water (e.g., swimming) or contact (e.g., combat sports). The devices will be placed in the hip because it seems to be more effective in classifying the intensity of PA and the movement patterns. The accelerometer will be programmed for 60 seconds epoch length. Each day will only be considered when recording at least 600 minutes of activity, i.e., 10 hours. The daily time spent in light, moderate and vigorous-intensity activities will be calculated;
6. Exercise intensity - Investigators will monitor exercise intensity with the perceived exertion Borg Scale. This scale has been used in RCT with HIIT;
7. Cardiorespiratory Fitness (CRF) - To assess VO2max the Chester Step Test will be used. This field test proved to be reliability to estimate CRF and has been used in controlled trials with the overweight population;
8. Enjoyment - To measure the enjoyment, the investigators will use Portuguese version of the the Physical Activity Enjoyment Scale (PACES);
9. Quality of life - To assess the quality of life it will be used the Portuguese version of the SF-36 Questionnaire. This questionnaire evaluates 8 dimensions: physical function, physical performance, physical pain, general health, mental health, emotional performance, social function and vitality;
10. Eating Behaviour - The eating behaviour will be assessed through the Portuguese version of the Three-Factor Eating Questionnaire - R21 (TFEQ - R21) questionnaire, consisting of 21 items and three subscales: cognitive restraint, uncontrolled eating and emotional eating;
11. Satisfaction with the study - A satisfaction Likert-scale questionnaire that the participants should fill out, aims to assess the satisfaction with the exercise classes. The Likert-scale questionnaire will be created for this purpose.

Timing: According to the inclusion/exclusion criteria mentioned, the participants will be assessed to be eligible to participate in the study. In December 2021, participants will be randomized and allocated in three different groups (CG, Home HIIT and Class HIIT). The intervention will begin in December 2021 and end in September 2022. The close-out of the study will be in September.

Inclusion Criteria:

• female individuals aged between 25 and 50 years old, at the time of selection;
• have a BMI equal to or greater than 25kg/m2;
• have the ZOOM application (San Jose, USA) and a 2x2m2 space at home for the practice of HIIT;
• who present, in their own form, authorized consent to participate in the referred study. Only one person per household will be allowed to be included.

Exclusion Criteria:

• having any health problem and/or condition that limit the implementation of an HIIT program;
• taking medication that influences the variables to be studied;
• being involved in any type of exercise intervention/program;
• being in pre-menopause or menopause period.

Overweight women between 25 and 50 years old.

Yes. We will publish the protocol and study results.

Starting 6 months after publication

The participants will be randomized and alllocated in one of the three groups (control or experimental HIIT Homebased or experimental HIIT traditional)