Optimization of body balance indices according to Body Mass Index categories during physical education lessons for university students

Authors’ Contribution: A – Study design; B Data Statistical Manuscript Abstract Background and Study Aim Body stability is an important factor in the manifestation of human motor skills. The purpose of the research is to evaluate the efficiency of balance exercises, applied for 28 weeks, with a frequency of one activity / week, on a group of undergraduate students of the “Dunărea de Jos” University of Galați. Material and Methods 195 subjects participated (99 males and 96 females), divided for analysis into 3 groups (underweight, N = 21, age = 20.16 ± .38, BMI = 17.46 ± .20); (normal weight, N = 111, age = 20.30 ± .21, BMI = 21.70 ± .17); (overweight / obese, N = 63, age = 19.90 ± .18, BMI = 30.69 ± .61). The tests were applied at 3 distinct times: initial T1 at the beginning of the academic year, intermediate T2 towards the end of semester 1 and final T3 at the end of semester 2. 3 static balance assessment tests were used (One leg standing test with closed eyes, Stork test and Flamingo test), respectively 4 tests to evaluate the dynamic balance (Bass test, Functional reach test, Walk and turn field sobriety test and Fukuda test). Results ANOVA with repeated measurements and the differences between the test moments highlight in most cases values of F associated with significant thresholds (p <0.05), so there is an improvement in results for all 3 groups. The differences between T1 and T2 tests are larger than those between T2 and T3, so for almost all tests the progress is higher in the first semester, and in semester 2 there is a slight reduction, as a result of adapting to the proposed exercises. Even if they progress significantly, the group of overweight people has obviously weaker average results than normal weight and underweight people, signaling numerous individual cases that have problems in maintaining static balance and commit errors in dynamic balance tests. The better performances of the underweight in 3 cases (One leg standing test, Flamingo test Fukuda test and Walk and turn field sobriety test) cannot be generalized due to their small number compared to the other 2 groups, and this aspect can be considered as a new direction of investigation. Conclusions There are premises for a favorable evolution of the balance indices for the group tested in this age group, but it must be taken into account that the low initial fitness level (generated by the lack of concerns for a lifestyle based on physical activities) is a factor that facilitated these less spectacular advances, but still statistically significant.


Introduction 1
The balance of the body is important in maintaining different positions and the correct execution of movements, and along with increasing postural muscle strength has a decisive role in the stability of the body of obese people, who have high risks of falling [1,2,3]. The sense of balance is fundamental in ensuring the technical correctness of the procedures in sports activities and reducing the risks of injury [4,5,6]. The importance of dynamic balance training for young athletes in Malaysia as a factor in injury prevention is highlighted by Lee et al. [7]. The use of balance assessment tests (as elements of the functional fitness battery) may signal possible postural control deficits, induced PEDAGOGY by the cervical proprioceptors, whose feedback improves the balance on the non-dominant leg of Taekwondo fighters, compared to untrained people [14]. Ways to optimize body stability for different age groups are frequently sought.
The introduction of additional actions with the additional demand for attention can affect the balance. Frequent use of mobile phones for Taiwanese students (texting while walking) affects dynamic balance performance and reduces postural stability, but it has been found that younger subjects can easily prevent falls and adapt more quickly to such tasks, according by Nurwulan et al. [15].
For children and adolescents (9-18 years) there is an improvement in postural balance with increasing age, for groups of athletes aged 9-12 years are found better values for girls, but this difference between genders is no longer reported for the group 13-18 years [16]. The use of hover-boards has beneficial effects on the static balance (One leg standing test and Stork test), respectively dynamic (Balance beam walking test) at the level of young Italian football players, being indicated the use of these devices also in other sports [17]. Playing handball as a recreational sport for postmenopausal women (49-79 years old) facilitates the improvement of postural balance and bone health, reducing the risk of falls and injuries for this category of population [18].
The comparison of performances between athletes (football players) and groups of sedentary students of the same age confirms the significantly better values of athletes, so the involvement in physical activities improves balance [19]. The associations between balance issues and the low level of fitness of African children is highlighted by Verbecque et al. [20]. The authors indicate that there is a high chance of impaired balance with increasing BMI values, so the preventive role of physical activity in maintaining and reducing body weight is vital. The decrease in leg muscle strength and antero-posterior balance performance for pubertal children (overweight and obese classes) is highlighted by Alhusaini et al. [21]. The application of the Bruininks-Oseretsky test battery on young people (10-21 years old) highlighted the difficulties related to balance for the overweight, compared to the normal-weight one [22]. For adults, there are difficulties in maintaining balance for the inactive and obese, so physical activity has the role of improving these problems [2,3,23]. For the obese, a greater balance is identified compared to the normal weight, and the reduction of body weight in these cases (through physical exercise) is a solution that ensures an improvement of the postural control [24]. The idea is supported by another study, where increasing muscle strength for obese people does not necessarily bring an improvement in balance, the weight loss being more important [25].
A comparison between obese young Japanese girls (9 years old) and adult men showed poor results of girls in static and dynamic balance tests, with high chances of injury and reduced control of movements during motor activities [26]. In obese and overweight young adults, poor results are confirmed in dynamic balance tests, with obvious mid-lateral displacement of the center of gravity, major risks of falling and higher time required for performing various motor tasks, aspects to which are added postural problems at the level of the spine [27].
Purpose of the Study. The study purpose was to evaluate the efficiency of balance exercises, applied for 28 weeks, with a frequency of one activity / week, on a group of undergraduate students of the "Dunărea de Jos" University of Galați, divided into 3 BMI categories (underweight, normal weight and overweight).

Participants.
The studied group consists of 195 students from "Dunărea de Jos" University of Galați (99 males and 96 females included in the undergraduate study programs of years 1 and 2 of the Faculty of Automation, Computers, Electrical and Electronic Engineering, respectively Medicine and Pharmacy), made up by random selection to ensure numerical balance by gender and divided for data analysis into 3 categories: underweight (N = 21, age = 20.16 ± . 38 [30,31,32,33]. The batch testing was performed during the academic year 2018-2019, in 3 distinct stages (T1initial testing, at the beginning of the academic year; T2-intermediate testing, in the 12th week / December, before the winter holidays; T3-final testing, at the end of the academic year). Students who were absent from physical education lessons were not included in the statistical calculation, in order to highlight the efficiency of the motor structures proposed for the development of balance. Participants were advised not to engage in stressbased efforts prior to testing, so that muscle and nerve fatigue does not affect the value of the results.
Training program. The exercise program was implemented over a period of 28 weeks, with a frequency of one activity per week, the structures oriented towards the development of balance being explained and practiced for 15-25 minutes in each lesson, with variable and individualized dosage, according to the effort potential of each participant. Table 1 selectively presents proposed exercises to optimize the level of static and dynamic balance, with the mention that they have been alternated and changed during the activities, in order to avoid capping the results, by adapting the participants to the proposed stimuli.

Statistical Analysis.
The statistical calculation was based on the use of Anova parametric techniques with repeated measurements, separately for each subgroup analyzed (underweight, normal weight and overweight / obese). We preferred to include the overweight and obese in a single category, in order to simplify the statistical analysis and reduce the resulting data volume. Data on: Maucly's Test of Sphericity were synthesized, with the application of the Greenhouse-Geisser correction factors (for e <0.75) and Huynh-Feldt (for e > 0.75) when the sphericity could not be assumed, the values of F and associated significance thresholds (sig.), size effect expressed by Partial eta squared (h 2 p), the differences between the average values between the test moments and their significance, using the Bonferroni correction factor [34,35]. The confidence interval was set at 5% (p <0.05), according by Murariu, Opariuc [36,37,38].

Motor structures proposed for the development of static balance
• From standing, lunging by making a step back with your palms on your hips and holding the position with your arms up. • From sitting with the palms on the hips, raising the right knee and thigh parallel to the ground, maintaining the position for 5-30 seconds, then the action is repeated for the left leg. Same with lifting a leg outstretched forward / sagittal plane, with the heel at a distance of 10-30 cm above the ground.
• From standing on one leg, throwing a tennis ball vertically and holding the arm on the side of the support leg. The same goes for holding the raised leg with the arm. Same with throwing the ball from one hand to the other. • Maintaining balance by flexing and extending the knees from sitting on the platform or balance ball / bosu balance trainer.
• From standing on one leg, bending the torso forward and touching the tip of the supporting leg with the opposite arm, the free leg is bent / flexed from the knee and oriented / lifted back. • From standing on one leg, slight half-flexion with return and arms outstretched sideways, vertically or in other planes. • From standing facing the wall, lifting on tiptoes with a slight bend of the torso forward to the limit of imbalance, then balancing by pushing with the palms towards the wall.

Motor structures proposed for the development of dynamic balance
• Moving on various hardness surfaces (soft, semi-hard or hard mattresses), jumping from one foot to the other while maintaining balance.
• Successive jumps on one leg, over a drawn line or a cord stretched on the ground, maintaining the position 2-3 sec before the next jump. On return, the detachment leg changes. The same with alternate jumps, from one foot to the other. • From standing sideways to a column of 5-6 bottles, spaced 50 cm apart, jump on one leg next to each bottle, maintaining balance and placing a glass on it. The same with zigzag / snake jumps between bottles. The same jumping back to each bottle. • Running bypassing milestones at 360 0 alternating the direction of rotation: left / right. • Walking on the narrow side of the gym bench with variable speed, with jumps over various objects and turning at 90, 180. 360 0 . The same by moving backwards on the gym bench. • Jumps on one leg or from one leg on the other, on different signs / markings drawn on the ground, maintaining the unipodal balance for 1-5 sec. The same with jumps on one leg, in circles arranged under different variants / arrangements on the ground. q w e r asdfghh

Results
The values of the Anova parametric test with repeated measurements (table 2) indicate significant progress at the level of the 3 groups for most tests (F values correspond to thresholds p <.05), except for the group of underweight in Walk and turn field sobriety test, where p = .329, statistically insignificant value. Partial eta squared scores indicate a strong influence of the applied balance exercise program on the results, with the highest values for all 3 groups in the Bass test and Functional reach test (for underweight, in the Bass test, 81.5% of the variance is explained by the intervention of the proposed program, and for overweight, at the Functional reach test, 81% of the variance is attributed as an effect of the applied program). It should be noted that for the rest of the tests, at the level of the group of normal weight, stronger influences of the program are registered (through the values of (h 2 p) than at the level of the groups of underweight and overweight. The weakest effects of balance exercises are found in the Walk and turn field sobriety test and Fukuda test for underweight and normal weight, but with strong effects on overweight.
Comparison and analysis of average differences in pairs at the level of the underweight ( The situation is similar for the group of normal weight (table 4) with larger differences for the first semester of preparation and smaller for the second, but significant for most data pairs. In the case of the Walk and turn field sobriety test, only for the initial test-final test pair there is significant progress (so at Graph 1 shows the average performance values of the 3 batches at the final tests. Overweight people have the weakest results in tests to assess static and dynamic balance, but their progress (statistically confirmed) does not allow the approach to the values of normal weight and underweight. They have the shortest holding times at static balance, the lowest score on the Bass test, they make the most errors on the Flamingo test and the Walk and turn field sobriety test, and they have the highest rotation scores around the body axis on the Fukuda test. It is interesting that the underweight group has results close in value to that of the normal weight in most tests and even slightly better than them in One leg standing test, Flamingo Fukuda test and Walk and turn field sobriety test, which requires checks by studies on larger groups in this category, in order to generalize these results.

Discussion
Our study identifies the effectiveness of the diversified exercises proposed to optimize the level of balance, an aspect confirmed by other similar research.
Applying core training on unstable surfaces for 18-25-year-olds in Turkey generates gender *. The mean difference is significant at the .05 level; b. Adjustment for multiple comparisons: Bonferroni.
differences for dynamic balance (Y test), but not for the rest of the fitness components [39]. In order to reduce the risk of injury, for American football players are recommended exercises for vestibular, proprioceptive, neuromuscular, with eyes closed and open, respectively on various surfaces -stable and unstable [40]. The use of unstable surfaces improves the values of dynamic balance and reduces the static postural balance for 7-year-old gymnasts [41]. Exercises performed on stable ground are less effective than the variant of unstable surfaces, for women of the 3rd age (60-80 years), by applying a program of this type (12 weeks, with 2 workouts of 45 min./week and 25 minutes oriented to equilibrium structures) progress is achieved, according by Matla et al. [42]. Our program also included this kind of exercises, and the significant progress at the level of the 3 categories confirms their viability. The variants proposed by specialized studies for balance optimization are extremely varied. An improvement of the results by applying a Tabata training program (for young football players / ages = 23 years) is obtained for the Flamingo test, but without statistical significance, according by Ceylan et al. [43]. Other research highlights the role of various physical activity programs (combat sports, pilates) on increasing balance values and reducing the risk of falls in different categories of the population [2,3,6,44,45]. The type of sport practiced influences the values of balance. Higher values in the balance tests of young Turkish athletes who are involved in individual sports (karate, gymnastics, judo, table tennis) compared to those involved in team games (basketball, volleyball, handball), as well as the increase the performance of the dynamic balance as age increases are identified by Turkeri et al. [46]. A program of balance exercises applied to children (10-12 years), for 8 weeks x 3 sessions per week generated superior performance in the Flamingo test, but also the speed and agility tests [47]. For teenagers in Kosovo, in the Flamingo test, girls perform better only for the 14-15 years old age group, then boys get superior performance [48]. Balanced values between Montenegrin and Kosovo teenagers in the Flamingo test are obtained by Morina et al. [49]. Long-term application of fitness programs (3 years x 3 sessions / week x 90 min) and their combination with diet positively influences the performance of fitness tests, including the Flamingo test, for boys aged 8-11 years [50]. We obtained in this test the best results for underweight, followed by normal weight, overweight having the lowest performances.  A decrease in performance in balance tests is reported after the age of 50, and for the interval 20-49 years similar results are recorded, overweight women obtaining lower scores than normal weight [51]. The differences between obese and normal weight for One leg standing test and dynamic balance assessment tests are also reported among Chinese children aged 8-10 years [52]. Young obese PEDAGOGY people (21.7 years) have the poorest results in bipodal and unipodal balance tests, compared to normal weight and underweight, according by Ku et al. [53], aspect similar to our research. Young people (ages = 21 years) with concerns related to physical activities (moderate to vigorous intensity) have a lower balance area and implicitly a better balance, with higher values for testing with eyes open [54].
Comparisons between static balance values between female dancers with at least 7 years of activity and sedentary ones (18-23 years) indicate higher balance values for dancers and superior postural control [55]. An exercise program applied 5 weeks, to influence the dynamic balance in elderly and overweight women is proposed by Bellafiore et al. [56]. In this case, performance improvements are obtained for most of the people involved, as a result of the efficiency of the muscular structures and the visual system, which ensures the postural balance. The use of DCE / dynamic core exercise in the warmup part of physical education lessons for children at the beginning of puberty (10-11 years), for 6 weeks has favorable effects on balance and flexibility [57]. Other authors propose exercises with elastic cord at the level of elite gymnasts' girls (14 years), through an applied program 12 weeks x 18 hours per week + 2 hours dedicated to exercises with elastic cord, which generate favorable effects on body balance [58]. There are also researches that demonstrate the effectiveness of applying oriental techniques (Yoga asanas) for obese young people (21-25 years), for a period of 4 weeks x 3 sessions per week x 45 min / session. Significant improvements are found in the Functional reach test and One leg standing balance test [59]. Our study confirms the effectiveness of programs based on balance exercises for the age category investigated, even if it was applied with a frequency of one session / week, being in accordance with the other research previously analyzed, through the beneficial effects found.

Conclusions
The application of balance exercises generates performance optimization in the tests applied to all groups investigated, so they are prerequisites for increasing body stability in static and dynamic actions for university students. The progress made is not spectacular, but the fact that they are statistically significant is still a positive aspect. It should be noted that for most tests there is more progress between the initial and intermediate tests, and slightly less between the intermediate and final tests, as a result of a possible adaptation to the exercises proposed in the second part of the program implementation. Even if the group of overweight progresses significantly, its results are weaker than those of normal weight and underweight; this category having the biggest problems in maintaining the body in different positions, but commits most errors and has poor scores in dynamic balance tests. The fact that underweight people get results close to those of normal weight and for 3 even better tests (One leg standing test, Flamingo test Fukuda test and Walk and turn field sobriety test) must be interpreted with some reservations, their weight / representation in the study group requiring the repetition of the research on a much larger sample at the level of underweight. Favorable results can also be explained by the low initial fitness level of the group (without concerns about sports activities), which facilitated the progress made.
The limits of the study and new research directions. The high volume of data did not allow the presentation of differences in gender and between gender tests, or the analysis of the significance of differences between BMI classes / (independent samples), which are the subject of another scientific paper. It would be interesting to analyze the results of the battery of tests for students of the Faculty of Physical Education and Sports and whether reading the practical contents of the curricula generates significant improvements in performance related to balance (these data are already collected and will be statistically processed). The use of modern equipment and technologies (which investigate static and dynamic balance using sensors and baropodometric platforms) would facilitate a more nuanced investigation of the mechanisms that condition body stability and identify factors that reduce the value of performance in balance tests.