AN ANALYSIS OF SCHOOL PHYSICAL ACTIVITY IN ADOLESCENT GIRLS

The positive eff ect of physical activity on health is well documented (Strong et al., 2005; USDHHS, 2008). At the same time, it has been proven that a physically active child will grow to be a physically active adult with a high likelihood (Kraut, Melamed, Gofer, & Froom, 2003; McKenzie, 1999; Savela et al., 2010; Telama et al., 1997). There is a number of studies that deal with obesity in children and adults and that warn against constantly increasing obesity and physical inactivity (PI) and disea ses related to them (Goran, Reynolds, & Lindquist, 1999; Strong et al., 2005). Along with age, the level of PA in children and youth is decreasing (Duncan, E., Duncan, J., & Schofi eld, 2008; Riddoch et al., 2004; Tudor-Locke et al., 2009), with the biggest decline in intensive PA (Frömel, Chmelík et al., 2007). Regarding the decline of PA, the most risky group is adolescent girls (Duncan, E., Duncan, J., & Schofi eld, 2008). Adolescent girls are less active than adolescent boys (Armstrong et al., 1990; CDCP, 2008; Frömel, Novosad, & Svozil, 1999; Riddoch et al., 2004), however, according to Sigmund, Croix, Miklánková and Frömel (2007), the decline of PA is more apparent in boys than in girls. Frömel, Chmelík et al. (2007) have found that boys and girls who engage in some form of organized PA meet the health recommendations for PA signifi cantly more frequently than those who do not. When studying the decline of PA in adolescent girls, it is necessary to monitor the level of PA on weekdays and at weekends. According to Sigmund et al. (2003) who monitored PA in adolescent girls and boys, the decline of PA is apparent mainly at weekends. Similarly, Treuth et al. (2007) who monitored girls using ActiGraph found that girls spent more time in moderate and intensive PA on school days than at weekends. The decline of PA at weekends (Duncan, E., Duncan, J., & Schofi eld, 2008) supports to a great extent the role of school regarding the level of PA on school days. School related PA forms an important part of total PA on school days (Wickel & Eisenmann, 2007). AN ANALYSIS OF SCHOOL PHYSICAL ACTIVITY IN ADOLESCENT GIRLS


INTRODUCTION
The positive eff ect of physical activity on health is well documented (Strong et al., 2005;USDHHS, 2008).At the same time, it has been proven that a physically active child will grow to be a physically active adult with a high likelihood (Kraut, Melamed, Gofer, & Froom, 2003;McKenzie, 1999;Savela et al., 2010;Telama et al., 1997).
There is a number of studies that deal with obesity in children and adults and that warn against constantly increasing obesity and physical inactivity (PI) and disea ses related to them (Goran, Reynolds, & Lindquist, 1999;Strong et al., 2005).
Along with age, the level of PA in children and youth is decreasing (Duncan, E., Duncan, J., & Schofi eld, 2008;Riddoch et al., 2004;Tudor-Locke et al., 2009), with the biggest decline in intensive PA (Frömel, Chmelík et al., 2007).Regarding the decline of PA, the most risky group is adolescent girls (Duncan, E., Duncan, J., & Schofi eld, 2008).Adolescent girls are less active than adolescent boys (Armstrong et al., 1990;CDCP, 2008;Frömel, Novosad, & Svozil, 1999;Riddoch et al., 2004), however, according to Sigmund, Croix, Miklánková and Frömel (2007), the decline of PA is more apparent in boys than in girls.Frömel, Chmelík et al. (2007) have found that boys and girls who engage in some form of organized PA meet the health recommendations for PA signifi cantly more frequently than those who do not.
When studying the decline of PA in adolescent girls, it is necessary to monitor the level of PA on weekdays and at weekends.According to Sigmund et al. (2003) who monitored PA in adolescent girls and boys, the decline of PA is apparent mainly at weekends.Similarly, Treuth et al. (2007) who monitored girls using ActiGraph found that girls spent more time in moderate and intensive PA on school days than at weekends.
The decline of PA at weekends (Duncan, E., Duncan, J., & Schofi eld, 2008) supports to a great extent the role of school regarding the level of PA on school days.School related PA forms an important part of total PA on school days (Wickel & Eisenmann, 2007).
School related PA comprises of transport to and from school, PA during breaks, and PA in PE lessons.Moreover, the longer breaks there are during a school day, the more PA (Verstraete et al., 2006) children perform.Also, the more space children and youth have (m²) at school, the more PA they perform (Loucaides et al., 2009).Physical activity during breaks on a school day can have a similar health eff ect as a physical education lesson (Frömel et al., 2008).
Due to this reason, many authors argue for the potential of schools to increase PA in children and adolescents (Pate et al., 2006;PCPFS, 2009;USDHHS, 2010).In relation to the prevention of obesity and interventions enhancing PA, it is important to pay attention to school related PA (PA in PE lessons, transport to/from school, PA during breaks).
The aim of the study was to characterize school related weekly PA in adolescent girls and to identify the eff ect of the participation in PE lesson on the structure of weekly PA.

METHODS
The sample comprised 136 randomly selected girls (age 17.97 ± 0.6 years; body weight 57.76 ± 8.15 kg; body height 166.92 ± 6.9 cm; BMI 20.72 ± 2.52 kg/m²) from eight secondary schools in Poland in Katowice region in the school year 2009/2010.All girls gave their consent to the study.The girls were divided into three groups according to their participation in PE lessons.The division was made on the basis of results from ActiGraph and from record sheets of participating girls.Group 0PEwithout participation in PE lessons (n = 36), group 1PE with participation in one PE lesson (n = 45) and group 2PE -with participation in two or more PE lessons (n = 55) during fi ve school days.
The girlsʼ PA was monitored for one week (5 school days and 2 weekend days) using the ActiGraph GT1M acce lerometer, along with record sheets into which the girls recorded the time they put on and took off the mo nitor, the type and time of PA and PI (physical inactivity).This accelerometer is considered reliable for the monitoring of physical activity in adolescents (Kohl, Fulton, & Caspersen, 2000).The girls were monitored for 14 hours (± 2.14 hours) per day.The results from ActiGraph were processed using specially designed software "ActiPa2006" (Chytil, 2006), which described PA in girls according to their energy expenditure, PA intensity, number of steps, and the time spent doing each type of PA or PI.After the data had been processed, the girls received feedback in written form with comments.
School related PA (PA realized in the time period between entering the school in the morning and leaving the school in the afternoon) was divided into four categories according to its intensity in compliance with Pate et al. (1995), physical inactivity ≈ 1 MET, low PA = 1.1-3MET, moderate PA = 3.1-6 MET and intensive PA = 6.1-12MET.In no participants did we measure PA higher than 12 MET.
To carry out the statistical analysis of the data, STATISTICA 9.0 program was used.To compare the groups with diff erent participation in PE, Kruskal-Wallis ANOVA and coeffi cient "eff ect size" η² (Morse, 1999) were applied.Statistical signifi cance was set at the level of p < .05.
This study was approved by the Ethical Committee of the Faculty of Physical Culture at Palacký University in Olomouc.

RESULTS
School related physical activity accounts for 32% of total daily PA (steps/day) in the group 0PE, 33% in 1PE group, and 38% in 2PE group of the total daily PA.
Comparing the 0PE, 1PE, and 2PE groups regarding the PA intensity expressed in METs, we observe gradual growth of PA, with the 2PE group showing the highest intensities in all school related PAs (TABLE 1).Statistically and logically signifi cant diff erences between groups are found in low PA (1.1-3 MET) and intensive PA (6.1-12 MET).In the case of moderate PA (3.1-6 MET) no statistically and logically signifi cant diff erences were found between the groups.In physical inactivity (≈ 1 MET) no statistically and logically significant diff erences were found between the groups either.
When we compare the groups among themselves, the re is a statistically signifi cant diff erence between 0PE and 2PE (p < .001)and 1PE and 2PE (p < .001) in low PA, and also between 0PE and 2PE (p < .001)and 1PE and 2PE groups (p < .001) in intensive PA.
Walking and housework in second place are the ty pes of PA which the girls spent the most time with.When we compare these types of PA in each group, there is an diff erent order than in the case of school related PA.Group 0PE spent the most time with them, 1PE in second place and 2PE spent the least time (Fig. 1).The comparison of groups regarding the types of PA shows diff erences between the groups regarding their participation in PA and the types of PA they perform (Fig. 2).

DISCUSSION
The results show that girls participating in two or more PE lessons show higher levels of school related PA in total and spend more time performing intensive PA at school than girls participating in one or no PE lesson.At the same time, the school related PA expressed in percentage forms a larger part of total daily PA in the former group of girls than in the later two ones.Frömel et al. (1999) monitored PA in PE lessons at secondary and elementary schools, and identifi ed the lowest average PA intensity in girls at elementary schools (4.53 MET) and the highest in boys at se condary schools (5.28 MET).The measured values of PA were between 3.1-6 MET: moderate PA, e.g.gymnastics (4 MET), tennis-double (6 MET), basketball (not a competitive game -6MET), volleyball (not a competitive game: 6-9 players, 3 MET), golf (4.5 MET) (Ainsworth et al., 2000).Adolescent girls at Polish secondary schools spent, at school, only 10 minutes on average in PA of such intensity (group 0PE 8.6 min.;group 1PE 11.2 min.;group 2PE 11.5 min.).
All the girls spent most of their time in PI, on an average of 125 minutes (group 0PE 118 min.; group 1PE 122 min.; group 2PE 136 min.).Physical in activity included lying down, listening to music, reading in a vehicle, sitting, standing, watching TV, writing while lying down, etc. (Ainsworth et al., 2000).
Girls spent, in intensive PA of 6.1-12 MET at school, on an average of 0.3 minutes -group 0PE, 0.5 minutesgroup 1PE and 0.8 minutes -group 2PE.
Based on comparison with health recommendations, which suggest seven times a week of 60 and more minutes of moderate PA, and at least three times a week 20 mi nutes of intensive PA (USDHHS, 2008), we can argue that if the girls spent only 10 minutes on the average in moderate PA related to school, it seems to be rather an alarming fi nding.
In both moderate PA and intensive PA, our fi ndings show that adolescent girls are a group at risk threatened by an inactive lifestyle and the diseases caused by it (DH, 2004;Riley & Jones, 2007).

Limits of the study
The results from ActiGraph were assessed together with using the record sheets into which the girls recorded at what time they put on and took off the monitor and the type and time of PA and PI.This procedure de pends on the responsibility and precision of the participating girls and their perception of PA.
More detailed information about the mental state, psychological state and physical fi tness of the participants was not ascertained.
The content of physical education classes was not observed.

CONCLUSION
The study has confi rmed that school related PA (especially PE lessons) plays a signifi cant role in education and is irreplaceable regarding the level of total daily PA in adolescent girls.Further, it is necessary to establish such material and legislative conditions which would enhance adolescent girlsʼ participation in PE lessons and other types of organized PA.School related PA in Polish girls accounts for 34% of their total daily PA in school days.Considering the fact that adolescent girls spend about half a day at school, we can argue that interventions carried out in the school environment are crucial.
Among the interventions that would enhance school related PA in adolescent girls, we can suggest introducing at least one physically active 30 minute long break during the school day, maintaining the number of PE lessons, or other types of organized PA.Further, girlsʼ participation in organized PA outside of school should also be enhanced.

TABLE 1
Physical activity of girls (n = 136) at school according to its intensity (min.) in each group Legend: group 0PE -a group without participation in PE lessons, group 1PE -a group with participation in one PE lesson, group 2PEa group with participation in two or more PE lessons, Mdn -median, IQR -interquartile range, M -mean, SD -standard deviation H -Kruskal-Wallis test, P -statistical signifi cance, η² -coeffi cient "eff ect size", a -a statistically signifi cant diff erence between groups 0 and 2, b -a statistically signifi cant diff erence between groups 1 and 2