EVALUATION OF BODY MASS INDEX IN WOMEN WITH A SEDENTARY LIFESTYLE AND THOSE PRACTISING VARIOUS AMATEUR PHYSICAL ACTIVITIES, AND THE PREVALENCE OF MENSTRUAL CYCLE DISORDERS IN PHYSICALLY ACTIVE UNDERWEIGHT WOMEN

: Background: The aim of the research was to assess the body mass index in women involved in various forms of physical activity including


Introduction
Physical activity and optimal nutrition are among the most important and, at the same time, basic human needs. They are necessary for the maintenance of optimal health, which, in turn, affects the quality of life [1,2]. Physical activity is any body movement resulting from the work of skeletal muscles, leading to energy expenditure above the level of the resting metabolism rate [3]. It, therefore, covers all forms of physical activity related to physical effort, including physical recreation (e.g., amateur sports, running, dancing, or classes in fitness clubs), competitive (professional) sports, as well as physical activity at home and its surroundings (e.g., working in the garden, walking) [3]. Used regularly and with the appropriate intensity, increased physical exercise contributes to a reduction in subcutaneous and visceral fat, increases muscle mass, and helps control body mass index (BMI) within the normal range [2]. The World Health Organization's recommendations regarding physical activity undertaken to prevent chronic noncommunicable diseases for people aged 18-64 recommend moderate aerobic physical activity (walking, cycling, running, swimming, team sports, classes in fitness clubs) for a minimum 150 minutes per week, or high-intensity aerobic activity for a minimum 75 minutes a week. In addition, they also confirm that undertaking physical activity for up to 300 minutes a week provides additional health benefits [4].
The impact of sports training on the human body is indisputable. Physical activity is beneficial for the cardiovascular system, lowers blood pressure, leads to an increase in physical efficiency, and improves exercise tolerance. It has a positive effect on changes in the lipid profile, reduces obesity, lowers the concentration of triglycerides, and improves glucose tolerance. It also has a beneficial effect on the function of the endothelium, inflammatory processes, the coagulation system, as well as on the concentration of sex hormones. This all helps achieve and maintain healthy body weight, increase and improve endurance, muscle mass, and prevent the development of osteoporosis. In addition, physical activity affects the release of endorphins , which helps relieve stress [1][2][3][4]. Many studies [2,[5][6][7][8][9] have shown that lack of exercise and a sedentary lifestyle are predisposing risk factors for the development of chronic diseases, including cardiovascular diseases, metabolic disorders, and cancers [10].
Body mass index (BMI) is a commonly used index to classify body composition in adults [11,12]. It is defined as a person's weight in kilograms divided by the square of height in meters (kg/(m) 2 ). Basic body weight measurement and BMI calculation are easy to carry out and give a general approximation of the individual's body proportions. However, it should be remembered that obesity is associated with excess body fat and not with the relationship between height and weight, so BMI should only be used as a preliminary estimate of abnormal weight. Research [11] has shown, however, that the BMI value is not sufficient enough to assess whether the level of body fat indicated by the BMI in any person is actually associated with the risk of any disease. It has been shown that there are people with an increased percentage of body fat with a normal BMI and people defined as obese based on the BMI index, with a low body fat content and a high lean body mass, e.g., athletes, especially of strength sports. The assessment of tissue components, such as the percentage of subcutaneous or visceral adipose tissue, and water or muscle mass, is important from the point of view of nutritional needs, the analysis of the impact of physical exercise on the human body, developmental norms, etc. The assessment of the human body can be performed not only in terms of body morphology and structure but also in terms of chemical and tissue composition and dominant somatotype components. Despite the shortcomings, the simplicity of calculating the BMI index and the relative accuracy of the assessment of excessive fatness in overweight and obesity make the BMI index unquestionably the most popular method of estimating the health risk associated with being overweight and obese [11,12].
The authors of the study chose the BMI index for the analysis as it is a popular measure used in the general population and is easy to calculate. Scientific research should provide specific information that can be used in a practical way by the population, e.g., women undertaking various forms of recreational physical activity. Amateur sportswomen do not always have the opportunity to examine body composition in detail, including determining lean body mass and other important parameters. BMI, however, is a parameter that everyone can calculate for themselves and, despite the fact that it is not perfect and is criticized by many researchers, it does offer a certain picture and a specific numerical value that can be transformed into a particular category, e.g., underweight, normal weight, or obesity. Therefore, the comparison of the BMI index in the three groups of women, who undertake relatively popular forms of amateur physical activity, seemed interesting and conveyed a significant message for the women who were physically active. In addition, the authors of this study, knowing about the possibility of menstrual cycle disorders associated with physical activity (Female Athlete Triad) undertaken by both professional and amateur female athletes, decided to check how often menstrual cycle disorders occur in underweight women [13][14][15][16]. A menstrual cycle depends on many factors. One of them is a specific level of adipose tissue (22%) needed to maintain regular menstrual cycles [17], which is obviously influenced by physical activity. Insufficient level of adipose tissue, such as a reduction to below 17%, affects the regularity of the menstrual cycle, including secondary amenorrhea. This is a particularly serious problem for women involved in sports [13][14][15][16].

Methods
The aim of the present study was to assess BMI in women who engage in various forms of recreational exercise, including dancing, running, and exercising in fitness clubs, compared to women who led a sedentary lifestyle. It was assessed to what extent a given form of exercise helps maintain healthy body weight, and thus whether physical activity undertaken only recreationally can have a beneficial effect on the prevention of diseases of civilization caused by an increase in the amount of adipose tissue. An additional study aim was to determine the prevalence of menstrual disorders in physically active women with a BMI indicating undernourishment in order to assess which group of recreationally active women incurred the greatest risk for the female athlete triad.

Participants
There were 683 women who voluntarily participated in the study, with a mean age ± standard deviation of 32.0 ± 10.2 years. These comprised 3 groups of physically active women: 215 regular runners (Runners-R), 120 who trained regularly in fitness clubs (Fitness-F), 143 regularly involved in tango dancing (Tango-T), and a group of 205 women who led a sedentary lifestyle and declared a lack of any regular physical activity (Control-C).
The study excluded women who were not experiencing a menstrual cycle due to pregnancy, menopause, or other reasons not directly related to exercise, e.g., hysterectomy or polycystic ovary syndrome. Women with other factors that could interfere with the menstrual cycle, including oral contraception, were also excluded from the research. The absence of the above-mentioned factors affecting the menstrual cycle was reported by the women in response to the questionnaire used in the study. The authors of the research had no other way to verify the presence or absence of such conditions because the questionnaire was completed anonymously and the participants remained anonymous to the authors.
An incorrectly completed questionnaire also resulted in exclusion from the research. Amenorrhoea lasting more than 3 months after a period of regular cycles in a woman was classified as a menstrual disorder. It can, therefore, be assumed that the factor influencing the disorders of the menstrual cycle was physical activity exceeding the body's adaptive abilities, and/or too low availability of energy supplied with food compared to the energy demand in active women. Both of these factors contribute to sports-related menstrual cycle disorders.

Questionnaire
The proprietary online questionnaire used in the research was filled out by all the groups using Google Forms. The questionnaire was placed on Internet portals aimed at people who run, train in fitness clubs, and dance the Argentine tango. In the control group, the questionnaire, also using Google Forms, was distributed using the contact network of female students at one of the Krakow universities. The questionnaire included questions concerning, inter alia, the demographic data of the participants, type of training, number of training hours per week, number of years of training, no menstrual bleeding lasting more than 3 months, and known causes or diseases affecting the regularity of the menstrual cycle. The part of the questions was based on a validated tool that assesses early symptoms related to energy deficiency in women, namely Low Energy Availability in Females Questionnaire (LEAF -Q) [18].

Statistical analysis
Statistical analysis was performed using the SPSS 21 software program (Version 27.0, IBM Corp., Armonk, NY, USA). The results of female runners, women exercising in fitness clubs, dancing tango, and the control group were compared, and the possible correlates and predictors of BMI in these groups were examined.
Means, medians, standard deviations, minima, and maxima were used to describe numerical data (continuous) and whereas numbers and percentages we used for dichotomous and qualitative data. Comparisons of the four groups for numerical variables were performed using the analysis of variance (ANOVA) with Tamhane's T2 post hoc test and for dichotomous and qualitative ones with the chi-square test. The Bonferroni correction was used for Journal of Kinesiology and Exercise Sciences multiple comparisons. Correlations were calculated using Pearson's r correlation coefficients. Multiple regression analyses were used to analyze BMI predictors. Regression analyses were performed separately for each group of physically active women. In the control group, the correlation was limited as only one predictor (age) was available. In the group of runners, the predictors of BMI were age, number of years of training, average number of training hours per week, average number of exercise sessions per week, minimum distance, and maximum distance. In the group of fitness club members, the predictors of BMI were age, number of years of training, average time spent exercising per week, average number of exercise sessions, strength training, CrossFit, calisthenics, yoga, treadmill, bikes, cardio, organised fitness classes, and number of forms of exercise. In the group of tango dancers, the predictors of BMI were age, number of years of training, average time spent exercising per week, journeys away from home connected with dancing, number of dance marathons, and number of workshops excluding festivals.
In order to investigate the possible negative effects of increased physical activity on menstrual cycle disorders in female athletes, underweight women were selected from each group who had previously had regular menstruation for at least a year, had not entered the menopause and had no diagnosed diseases which could have had a significant impact on the monthly menstrual cycle. The criteria for exclusion from the group was the use of hormonal contraception. There were 23 such women in the control group, 10 in the fitness group, 4 in the tango group, and 14 in the running group. The characteristics of the women included in the calculations are presented in Additional File 1. The women who were underweight were asked whether their menstrual cycle had stopped for a minimum of three months. In each physically active group and the control group, the percentage of women with menstrual disorders was calculated relative to the number of underweight people. The absolute values between the groups were compared using the chi-squared test.

Ethics
Participation in the research was voluntary, anonymous, and in accordance with the Declaration of Helsinki. The participants were informed of the purpose of the research and their right to refuse to answer the survey questions. The research protocol was reviewed and approved by the Bioethical Committee of the Andrzej Frycz Modrzewski Krakow University (Permission number KBKA/93/O/2020).

Results
The age of the surveyed women practicing various forms of physical activity and the control group differed significantly between all the groups. The mean age was highest in the dancers (41.1 years), lower in the runners (34.7 years), even lower in the control group (29.0 years), and lowest in the women training in fitness clubs (21.5 years) (Tab. 1).
The BMI of women was significantly higher in the control group (23.6) compared to runners (22.3), the fitness group (21.9), and the tango dancers (21.5). There were also significant differences between the runners and the tango dancers. The body weight of the women studied was similar.
The percentages of underweight, normal body weight, overweight, and obese women in the different groups are presented in Table 2. Being underweight was most common in the control group, significantly more often than in the dancers. Normal body weight was the least frequent in the control group, and less frequent than in all exercising groups of women. The dancers significantly more often had normal body weight compared to runners and women exercising in fitness clubs. Being overweight was most common in the control group, significantly more often than in the dancers. Class I obesity was most common in the Control group, significantly more often than in dancers and women training in fitness clubs. Class II and III obesity was present only in the control group.
The runners exercised, on average, for 5.4 years, which was significantly more than for the women from the fitness group and less than for the dancers. The training sessions lasted on average 4.8 hours a week, significantly less than in the tango group. The frequency of training was on average 3.6 times a week. They exercised for 1.3 hours at a time, less than the women in fitness clubs (Tab. 1). The minimum single distance that was run was on average 6.8 ± 3.7 km (median = 5 km), and the maximum was 19.8 ± 12.1 km (median = 16 km).
There was a positive correlation between BMI and the age of runners (r = 0.18; p <0.01) and a negative correlation between BMI and the average weekly time spent on training (r = -0.21; p <0.01), the average one-time training time (r = -0.22; p <0.01) and the maximum distance which the runners ran (r = -0.19; p <0.01), see Additional File 2. Two variables turned out to be highly correlated: the mean one-time training time and average weekly training time (r = 0.81; p <0.01). The mean weekly training time was used for the regression analysis (Tab. 2). All predictors together accounted for 11% of the variance of the dependent variable of BMI. A statistically significant predictor was age, which was a positive predictor that explained 3.72% of BMI variance, and mean weekly training time, a negative predictor that explained 2.82% of BMI variance.

Journal of Kinesiology and Exercise Sciences
The fitness group exercised for a year on average, which was significantly less than the groups of runners and tango dancers. The training sessions lasted on average 5.4 hours a week, significantly less than in the tango group. The average training frequency was 3.6 times a week. During one training session, women from the fitness group trained for 1.5 hours more than the runners (Tab. 1). On average, women from the fitness group chose two different types of exercise (minimum one, maximum five). The percentage of women preferring a certain type of training was as follows: strength training -95.8%, treadmill, cycling, cardio training -62.5%, organized fitness classes -17.5%, CrossFit -8.3%, calisthenics -5.8%, and yoga -5.8%. In the fitness group, there was a negative correlation between BMI and the choice of calisthenics (r = -0.19; p <0.05), see Additional File 3.
Regression analysis showed that the mean number of training sessions was a positive predictor of BMI (Tab. 3). However, this result should be treated with caution due to the statistically insignificant results for the entire model.
Of all the women surveyed, dancers exercised for the longest time (7.2 years on average). Their average weekly exercising time was also longer than in the other groups of exercising women. It averaged 7.9 hours a week (Tab.1). Most of the dancers (85.3%) traveled away from home to perform dancing activities. During the year, they participated in an average of 19.2 ± 12.1 dance marathons (median = 11), 14.0± 18.4 dance marathons involving journeys (median = 7), and 24.9 ± 43.8 workshops excluding festivals (median = 9.5).
In the tango group, there was a positive correlation between BMI and age (r = 0.14; p <0.01) and a negative correlation between BMI and the number of years of training (r = -0.10; p <0.01) and the number of trips away from home (r = -0.22; p <0.01), see Additional File 4. Variables of the number of dance marathons and the number of dance marathons with journeys were almost completely correlated (r = 0.96; p <0.01). The number of dance marathons was used for the regression analysis.  Table 3. Standardized and non-standardized regression coefficients, semi-partial correlations, percentages of explained variance, and statistical significance of individual predictors in physically active groups Regression analysis showed that the average training time was a positive predictor of BMI (Tab. 3). However, this result should be treated with caution due to the statistically insignificant results for the entire model.
Due to the lack of exercise characteristics in the sedentary control group, no regression analysis was performed for them, but the correlation between age and BMI was determined (r = 0.41; p <0.001).
Women from all the groups were asked whether their menstrual cycle had stopped for a minimum of three months. The results were as follows: the lowest number of menstrual cycle disorders in the underweight group occurred in the control group (one person, 4.3%) and it was significantly lower than in the fitness group (five people, 50%) (p = 0.001). One person of the underweight women (25%) in the tango group and three women in the group of runners (21.4%) reported menstrual cycle disorders. These results did not differ significantly from the control and tango groups and from the control and running groups.

Discussion
The epidemic nature of overweight and obesity, especially in industrialized countries, is a serious health and social problem. It is also one of the key public health issues [19,20]. Obesity affects 20% of the world's population and is, therefore, classified as a disease of civilization [6]. In this study, it was shown that, in the group of women who had a sedentary lifestyle, obesity affected 11.22% of them, of which 2.44% were people with class II and III obesity. This is better than the global result, which may be due to the fact that the control group consisted largely of female students and their families. According to literature data, the higher the education, the lower the BMI [21][22][23]. This relationship is probably because people with higher education have greater knowledge about the impact of physical activity and a properly balanced diet on the human body. Despite the better-than-general-population results, it is worth emphasizing that in the control group, the percentage of obese people was significantly higher than in the training groups. There were 1.67% obese people in the fitness group, and, in the tango group, only 0.70%. The results in the group of runners were lower than in the control group (2.33% of obese female runners), but this result was not statistically significant.
The accumulation of adipose tissue in the human body depends on basal metabolic rate, i.e. the lowest metabolic rate in the human body needed to maintain basic life functions at rest [24]. The basal metabolic rate declines with age [25]. If a person does not limit their calorie intake from their diet, or does not increase their body's energy expenditure through physical activity, then, fat tissue will accumulate in the body with age as was confirmed by the results presented in this study. In the control group, leading a sedentary lifestyle, the BMI value increased the most with the age of the women surveyed. In the groups of runners and tango dancers, an increase in BMI was also observed with age, although to a much lesser extent than in the control group. In the fitness group, the increase in BMI did not reach statistical significance. Therefore, it can be hypothesized that physical activity reduces to some extent the age-related effect of a metabolic slowdown.
The results of this research showed that there is a correlation of the time of a run, the frequency of runs in a week, the distance of a run, with BMI. Probably, with the loss of unnecessary fat tissue and the decrease in BMI, exercise tolerance increases and it is possible to cover longer distances. In the fitness group, women with a lower BMI most often chose exercises using their body weight, i.e., calisthenics. For people with a higher BMI, these exercises are probably too difficult to perform. On the other hand, in the group of women dancing tango, a negative impact on BMI was found both in the number of years of dancing and the number of trips to milongas and/or dance marathons taking place away from home. Unfortunately, based on the training data, building predictive models was only partially suc- Journal of Kinesiology and Exercise Sciences cessful. In runners, the predictive model showed that in addition to the positive predictor of age, there was a negative predictor of the average weekly training time. In the case of the fitness group and tango dancers, the predictive models did not reach statistical significance. Among all the groups, the lowest and, at the same time, the most appropriate BMI was characteristic of the women who chose the attractive form of an artistic combination of art and movement, namely the Argentine tango (tango group). Despite the fact that in the case of dancing, it is impossible to indicate the typical features of training, dancing, in its own special way compared to other forms of physical recreation, forces participants to correct their body posture in order to make the appearance of the figure more attractive by, for example, reducing body weight. It seems that such a goal is achieved spontaneously when undertaking this form of physical activity. In the studied group, the women had been dancing on average for over 7 years, which means that this form of activity as a response to musical, and especially rhythmic stimulation, was particularly enjoyable for them. Dancing, undoubtedly, permits entry into a sophisticated and elite world with rules and etiquette. It is a multi-dimensional experience that affects many aspects of human life, including personal, social, and psychological. It connects the individual, the body, and the emotion with what is social, thus reducing social isolation and making it attractive for single people. Additionally, participation in many hours of milongas, festivals, or dance marathons, often taking place in different countries of the world, is an intercultural experience and a place for making new friends. Despite many interesting aspects of being a dancer, it is not a form of movement for everyone, because it is practiced mainly by independent and financially stable women, who have a lot of free time [26].
In the remaining groups of physically active women, such a long involvement in their forms of physical activity was not found. The effects of their training and its impact on BMI were slightly worse, but still better than in the control group, i.e., women leading a sedentary lifestyle. It is worth noting that both the correlation and the predictive models indicate the need for involvement in training (an average weekly training time) in order to achieve satisfactory results. In this study, fitness training was preferred by younger women over tango and running. Perhaps this is due to the fact that in Poland, fitness clubs did not develop until 2000, so slightly older women may not feel comfortable in such places, because they have not received the cultural message that this is a place for them. Today, however, fitness clubs try to reach people of all ages and encourage them with an individual approach. The BMI of women in the fitness group is lower than in the control group. Therefore, if one prefers this form of exercise, it is also effective in normalizing BMI.
The development of fitness clubs has introduced highly specialized places into the sports culture so that different forms of physical activity can be selected by the exercising person. Modern fitness clubs have become a place of physical activity for adults, children, and teenagers, and the choice of various forms of training, both organized and individual, is almost unlimited. Workouts in fitness clubs are mostly planned and varied, including general development exercises, perfect for people aiming to reduce their level of body fat. Training for health, rather than typical sports training, is often carried out in clubs. This is focused, however, on developing general mobility, especially closely related to health and the prevention of diseases of civilization. Fitness clubs employ not only personal trainers who select training based on the results of body composition analysis, but also dieticians, who plan a nutritional program closely corresponding to the planned physical training. Such training is not only a safe but also an effective form of physical activity that can bring measurable health benefits. In the case of obese people, such exercises are more acceptable, better tolerated, and much safer for the musculoskeletal and cardiovascular systems [27,28].
In the present research, the Authors also focused on another aspect related to physical activity, namely underweight [29]. As the research of other authors [13][14][15][16] has shown, the low availability of energy in the female body is a key factor in the etiology of the female athlete triad (FAT), i.e., the interrelationship between eating disorders, amenorrhea, and osteoporosis. Sport-related menstrual disorders are complex physiological conditions that can have serious consequences for the health of young female athletes, including their future fertility and their ability to become pregnant. Physically active women are under social pressure to have low body fat and to be slim. In order to achieve their ideal body weight, they follow radical eating plans and restrictive diets without consultation with a dietician. As a consequence, this leads to an insufficient level of energy intake needed to maintain the high energy expenditure needed to practice sports, which in turn has a negative impact on the entire body, especially in a young woman of reproductive age. The threshold of energy availability, below which the clinical consequences for the athlete's health have been established, was defined as the availability of 30 kcal/kg/day free fat mass, which corresponds to the resting metabolism [13][14][15][16]. A possible problem of energy deficiency can be seen in the fitness group, in which half of the underweight women reported menstrual cycle disorders, while in the control group, this was only 4.3%. Protection of reproductive functions is better in the group of underweight tango dancers and runners, where menstrual cycle disorders affected 25% of underweight women from the tango group and 21.4% of underweight women from the group of runners. necessary to take vigorous measures to prevent its pathological effects. This situation also imposes an obligation on healthcare professionals to take preventive actions. The aim of such activities is to increase community awareness of the effects of the development of overweight and obesity on health and to provide information on healthy activities, such as undertaking physical activity and changing existing inappropriate eating habits. Appropriate recommendations should also be addressed to children and adolescents with a healthy body weight, as being slim at an early age does not exclude being overweight and obese in the future. Additionally, sports clubs should be encouraged to promote general development training aimed at reducing body fat.
Limitations of the study. The conclusions from this research were developed on the premise of cross-sectional research based on a simple BMI index. This has the advantage that a large amount of data can be collected in a relatively short time, which reduces the risk of randomness in the selection of the group for research. At the same time, this research has certain limitations. All the data obtained from the surveys was self-reported. BMI is only one indicator and does not account for the body fat and lean body mass needed for good health. Moreover, in this type of research, it is only possible to determine the BMI in people exposed to certain factors (running, fitness, dancing, sedentary lifestyle, age, training time), but the direction of the relationship cannot be clearly indicated. For example, is the lower average BMI in the physically active groups compared to the control group due to physical activity, or, vice versa, do people with a lower BMI undertake a given physical activity? An unambiguous answer could be provided by the observation of changes in BMI over time in individual groups, which would constitute a valuable extension of this research and certainly would become another research issue. However, based on the current knowledge about the impact of physical activity on the human body, which complements the results of this study, the conclusions were drawn, as presented below.

Conclusions
Regular physical activity, regardless of the type of training, reduces the value of BMI. In addition, it has a normalizing effect by reducing not only the percentage of overweight and obese people but also the percentage of those underweight. Physical activity reduces the negative impact of age on BMI, which is associated with a metabolic slowdown and the accumulation of adipose tissue in the body.
Compared to the other groups, the most normal and at the same time the lowest BMI was found in the Argentine tango dancers (tango group). Compared to other physically active groups, the BMI of runners was most dependent on training parameters.
The risk of the female athlete triad occurred in the fitness group, with half of the underweight women reporting menstrual cycle disorders.
Funding: This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.