Effects of high-intensity interval training on the anthropometric profile of overweight and obese adult women

Results: The adherent group (≥75% assistance) was composed by 16 participants, while the non-adherent group (assistance <75%), by 8 participants. No significant differences were found among both groups previous to and after the intervention (p≥0.05).The non-adherent group did not show any significant change, while the adherent group improved (p<0.05) their variables of weight (p<0.001), BMI (p<0.001), fat mass percentage (p<0.001), muscle mass percentage (p<0.001) and visceral fat percentage (p=0.020) after the intervention.


Introduction
Chile has evolved and its economy, technology and culture have progressed in such a way that, in recent decades, it has positioned itself as a developing country.However, there is an alarming increase of chronic non-communicable diseases: 93% of women are sedentary and 64% are overweight or obese (1); both pathologies are associated with the development of insulin resistance, type 2 diabetes and cardiovascular disease (2)(3)(4)(5).The traditional pharmacology has not provided an effective response to battle obesity, instead, physical activity has proven to be one of the most effective solutions to counteract the effects associated with this condition (6).This benefit grows if the activity is performed regularly and intensity increases (7).
Obesity is defined as an excess of body fat or adipose tissue, and is produced by the increase in energy consumption and the reduction in caloric expenditure (8).This condition generates a series of processes that develop resistance to leptin, resulting in a vicious cycle of weight gain induced by genetic and environmental factors (9).
Physical exercise has been proved to be one of the most effective ways to prevent and treat modern chronic diseases (10).When training is aerobic, although beneficial health effects are generated, high volumes of exercise are required to produce significant changes in the body; taking into account that the lack of physical activity of the population is mainly caused by lack of time (11), considering methods that produce more sudden and profound effects is necessary.Lowvolume, high-intensity interval training (HIIT) should be considered as a method for battling the negative effects of chronic diseases associated with lifestyle (12,13), as there is evidence that the accumulation of a variety of HIIT is effective for improving cardiopulmonary fitness, VO2max ( 14), metabolic capacity and insulin sensitivity (15,16).
The purpose of this study was to determine the effects of a highintensity interval training program on the anthropometric profile of overweight or obese women.

Materials and methods
Participants 24 adult women, aged 26 to 49, voluntarily participated in this study and went through a HIIT program for two months, in the facilities of Universidad Mayor, Temuco Campus; 16 participants were overweight and 8, obese.The invitation was made through voluntary and free registration in three exercise sessions per week (24 sessions in total).
The study design was quasi-experimental and two study groups were created according to the percentage of assistance to the program by the participants: the adherent group (AG), with attendance to exercise sessions ≥75% (minimum 18 sessions, n=16, age: 38.4±13), and the non-adherent group (NAG), with assistance <75% (less than 18 sessions, n=8, age: 32.2±6).Each participant acted as selfsupervisor after comparing the pre and post intervention.
The protocols coincided with the Declaration of Helsinki of 2013; the study was approved by the School of Nutrition of Universidad Mayor and each participant signed an informed consent to participate in the research.
Inclusion criteria included female subjects, aged 18 to 60 and at least three of the following factors: 1) high percentage of total fat >21%; 2) BMI >25, 3) sedentary lifestyle with the aim of performing <50 minutes per week of physical activity, and 4) percentage of muscle mass decreased by <40%.
Exclusion criteria considered the presence of any history of osteoarticular or ischemic disease, arrhythmias, tachycardias or chronic obstructive pulmonary disease that prevented doing HIIT exercises.

Procedures
Weight, muscle mass percentage (% MM), body fat percentage (% BFP) and visceral fat were determined through a double bioelectrical impedance assessment -using an bioelectrical impedance meter OMROM HBF-510LA-, barefoot, in light clothes and without metal objects.Height was determined with the aid of a precision height rod -Health o Meter®, USA-, graduated at 0.1mm; to calculate body mass index (BMI), the Quételet formula was used.Overweight was classified as 25.0-29.9kg/m 2 , and obesity as ≥30 kg/m 2 .

Design of the intervention program
An interval exercise program with the 1x2x3 method (17) was designed; three sets per exercise were run for 60 seconds, each with an intensity that induced muscle failure at the end of this period and two minute breaks between sets.This methodology is similar to other studies (18,19).
The exercises were focused on abdominal muscles and knee and hip extensors, and they were performed with multi -joint movement chains (Table 1).The progression of the exercises was done to break the adaptability of the study subjects to the accumulation of stimuli.

Method
One-minute exercise -two-minute passive rest to reach recovery pulse -three repetitions three times a week, on alternate days.

No equipment implementation is required
Source: Own elaboration based on the data obtained in the study.

Statistical analysis
Data are presented as mean ± standard deviation.All variables showed normal behavior (p≥0.05) and were measured through Shapiro Wilk test.A Student's t-test was used to evaluate pre-and post-intervention differences and for comparison between groups and independent groups.All analyzes were performed using SPSS version 22.0 and the confidence level was 95% (p<0.05).

Discussion
The purpose of this study was to determine the effects of a of high-intensity interval training program on the anthropometric profile of 8 overweight women and 16 obese women.The results indicated that the implementation of this program or training method, without the use of specialized equipment, allowed achieving changes in body composition, especially in reducing the fat mass of the adherent group.Overnutrition was associated with the development of insulin resistance and risk factors for cardiovascular disease (20).In this research, weight and BMI reported changes after eight weeks of HIIT (p<0.001),results that differed from other studies where similar methodologies were applied but failed to achieve significant changes in nutritional status (21,22); higher weight losses in subjects with obesity and morbid obesity were reported only in cases in which patients also received counseling and nutrition education (23).In addition, fat mass percentage significantly decreased by 5.02% in the adherent group (p<0.001).
The research conducted by Zhang et al. (24) implemented a 12-week training program with Asian women that included highintensity sprint and showed a decrease in the percentage of body fat, thus making HIIT the most effective method to control visceral and subcutaneous fat.The study by Kordi et al. (25), with sedentary women, proved that high-intensity interval training is an appropriate method for reducing body fat and improving anthropometric indices; likewise, Mancilla et al. (26) implemented this method on subjects with impaired glucose and excess weight, achieving a body fat reduction of 4.2kg.Postmenopausal women showed similar results through aerobic and overload exercise (27) and brisk walking (28).
In this study, muscle mass increased by 1.25%, similar to other groups of study with pre-diabetic predisposed subjects (29), where resistance exercises were applied until muscle failure for three months.A group of elder Japanese women proved that when obesity is combined with muscle weakness, there is a greater risk of developing mobility limitation than with only obesity (30), which is why it must be a priority in the treatment of women with this condition if quality of life is intended to improve.
In the research by Zapata-Lamana et al. (31), performed with adult women for three months, a physical exercise program, similar to the reported in this study, was implemented; improvements in cardiovascular health were observed when blood lipids and cholesterol were significantly altered.
This research allowed producing significant changes in the variables studied without requiring a high duration per session, which confirmed that this type of HIIT methodologies are timeefficient, improve muscle function and produce skeletal muscle adaptations that result in an increased fat and glucose oxidation (32)(33)(34)(35); this is evident in the increase of % MM and the decrease of BFP% of the studied overweight or obese women.
It is important to incorporate, for future research, psychosocial variables to assess, from a holistic perspective the effect of physical exercise as the main limitation of this study is that only anthropometric variables were considered.

Conclusions
The intervention conducted in this study improved the anthropometric profile of women with overnutrition subjected to intervention and that accomplished adherence to the program (>18 sessions); similarly, the patients significantly reduced their weight and body fat (p<0.001).It is noteworthy that this program managed to meet the target without requiring additional equipment.
The evaluation of plasma levels, aerobic capacity and blood pressure are planned for future research in order to further complement the benefits of this program.

Figure 1 .
Figure 1.Significant variations -adherent group.Source: Own elaboration based on the data obtained in the study.

Table 1 .
Exercise protocol used in the intervention.

Table 2 .
Features of pre and post high-intensity interval training intervention.
% MM: muscle mass percentage; BMI: body mass index; V%: percentage change between pre and post intervention.Source: Own elaboration based on the data obtained in the study.