Adolescents’ physical activity levels on physical education and non-physical education days according to gender,age,and weight status

Abstract

All Latin-American countries are affected by the lack of physical activity and its consequences on youth. Chile’s population has shown troublingly low levels of moderate-to-vigorous physical activity. This is the first study using objectively measured physical activity levels in Chilean adolescents. The objectives were to compare the compliance with daily recommendations of moderate-to-vigorous physical activity between physical education and non-physical education days, and to compare physical activity levels according to gender, age and weight status. A total of 123 Chilean secondary students (52 girls and 71 boys; 13.5 ± 0.7 years old) participated in this study. Physical activity was registered by GT3X accelerometers during an entire week. Results showed that there was a significant increase in the proportion of adolescents achieving the daily recommendation of moderate-to-vigorous physical activity on physical education days (23.6%) than on non-physical education days (14.6%) (p ≤ 0.05). Boys and older adolescents presented statistically higher levels of moderate-to-vigorous physical activity on physical education days than on non-physical education days. No differences were found in weight status comparison. Physical education has been found to be a crucial element in achieving the daily recommendations of moderate-to-vigorous physical activity. Diverse strategies in order to increase the moderate-to-vigorous physical activity in physical education according to the factors analysed are reported and discussed.

Keywords

Accelerometry health behaviour moderate-to-vigorous physical activity secondary

Introduction

The majority of the world population does not reach the 60 min/day of moderate-to-vigorous physical activity (MVPA) levels recommended by the World Health Organization (WHO, 2010) (Cuenca et al., 2014). Consequently, the practice of physical activity is one of the main focuses for scientists and politicians regarding general public health (Gillis et al., 2013; Reiner et al., 2013). Personal (gender, age and weight status) and contextual factors (school or out of school) have been considered as crucial in the quantity and quality of physical activity practice of individuals (Viciana et al., 2016). School aged children, mainly at the secondary school level, have been found to be in a more worrisome stage due to the decrease of MVPA (Cocca et al., 2014; Currie et al., 2012), which has consequences along the life span of these adolescents regarding health and general quality of life (Longmuir et al., 2014).

The school context, due to its guidance by capable professionals and compulsory character (more than 95% of school aged children registered (Levin et al., 2001)), is considered an ideal setting for promoting higher levels of physical activity in youth (Viciana et al., 2015), among other educational objectives. Schooldays with physical education (PE) have been identified as having higher levels of MVPA than weekdays without PE and weekend days (Brusseau et al., 2011). For instance, according to the Eurydice Report of the European Commission (European Commission/EACEA/Eurydice, 2013), 80% of European school aged children practise MVPA only in their schools, and do not compensate the lack of physical activity in their leisure time (Brusseau et al., 2011). Therefore, PE is considered crucial in contributing to the daily recommendations of 60 min/day of MVPA (Viciana et al., 2015; WHO, 2010).

The problem of physical in activity and its consequences in youth obesity has been shown in previous studies throughout all Latin American countries (e.g. Álvarez et al. (2013) in Puerto Rico, or González et al. (2014) in Colombia). In Chile, obesity has increased exponentially, being currently at 23% for six year olds (Kain et al., 2014), and reaching 86% of sedentary behaviour in the adult population (Government of Chile, 2013). However, studies with Chilean adolescents have been carried out with a self-reported measurement of physical activity (Burrows et al., 2008; Chilean Ministry of Health/WHO, 2005; Muros et al., 2016), despite its limited validity in youth (Shepard, 2003; Stenferd and Goldman-Rosas, 2012). Other studies were carried out with pedometers, but using samples of children instead of adolescents (Godard et al., 2012; Moreno et al., 2015). For instance, the Scholar Health World Survey carried out in Chile with 8131 adolescents between 13 and 15 years of age in municipal and subsidized schools from Tarapacá, Biobío, Valparaíso and the Metropolitan area detected only 15% and 8% of boys and girls as active enough regarding the 60 min/day recommendation, respectively, with only 40% of boys and 20% of girls practising MVPA out of school (Chilean Ministry of Health/WHO, 2005). Burrows et al. (2008) detected a drastic drop in MVPA levels for participants from six years old on, and obtained lower physical activity levels in children belonging to Chilean municipal schools (with only 90 min of PE class/week) than in children belonging to private schools (participants were involved in more MVPA time due to the structured physical activity and sports programs that they performed during their leisure time).

Among the studies with objective measurements of physical activity in Chile the study of Moreno et al. (2015), carried out with pedometers, compared MVPA between weekdays and weekend days of 250 children between six and nine years of age. Results showed that only 33% of boys and 15% of girls accomplished the daily recommendations of MVPA. There were no differences between non-overweight and overweight children in MVPA levels, but there were differences between weekdays and weekend days (50.5 min vs. 40.3 min, respectively), and between boys and girls during weekdays (54 min vs. 45 min, respectively) and weekend days (42 min vs. 37 min, respectively). Finally, studies using accelerometry in the general Chilean population are scarce and show opposing results. Vasquez and Salazar (2005) confirmed MVPA levels below the 60 min/day recommendation of the WHO (2010) (32 min of MVPA during weekdays and 24 min during the weekend days) in a sample of 24 obese children between three and five years of age using Tritac-R3D accelerometers. However, the study of Godard et al. (2012), carried out with 109 children aged 4–10 years, showed all participants achieving the recommended 60 min/day of MVPA. Moreover, the mentioned authors detected differences in MVPA between genders (106 min/day for boys and 64 min for girls) and weight status (102 min for non-overweight vs. 67 min for obese children). Therefore, it seems necessary to continue measuring physical activity levels objectively in the Chilean population in order to increase the scientific knowledge of this important variable of public health, especially in adolescents, where no previous studies were found.

It is important to address the real contribution of PE classes to the 60 min/day of MVPA in Chilean adolescents, as recommended by Moreno et al. (2012) in their future perspectives. To our knowledge, this is the first study that addresses objectively-measured physical activity levels with accelerometry in Chilean adolescents. Consequently, the objectives of this study were: (a) to compare compliance with the daily recommendations of MVPA (60 min/day) in Chilean adolescents between PE days and non-PE days; and (b) to compare the physical activity levels between PE days and non-PE days, as well as the influence of gender, age and weight status.

Methods

Participants

All participants belonged to four municipalized schools of Basic Education Level from Nuñoa Community of Santiago of Chile. The Community of Nuñoa was selected due to its being a neighbourhood representative of the population of Santiago of Chile, with middle–low socio-economic level families and a great number of adolescents concentrated in 10 closely allocated public schools. In addition to these characteristics, this neighbourhood was selected for the willingness of the students’ families and the PE teachers of the school centres to collaborate with the study.

An initial sample of 156 Chilean secondary school students, aged from 12 to 15 years, participated in the present study (69 girls and 87 boys; average age = 13.5 ± 0.7 years). The inclusion criteria were: (a) not having a physical problem related to muscular injuries or paediatric chronic diseases, and (b) presenting the corresponding signed consent by their parents or legal guardians. The exclusion criterion was not having at least one PE day and two non-PE days, with at least 600 min/day recorded by the accelerometer.

Measures

Objectively-measured physical activity levels

Objective physical activity was measured with a GT3X accelerometer (ActiGraph, LLC, Pensacola, FL, USA) that has shown high levels of reliability and validity (Vanhelst et al., 2009). The accelerometer registers and measures the variation of acceleration in a range of ∼ 0.95–2.50 g with three axes that collect information and calculate the magnitude vector. The output data is digitalized by an analogue–digital converter of 12 bits and 30 Hz that digitally filters the signal, limiting the frequency between 0.25 and 2.50 Hz. The counts obtained in a particular epoch are proportional to the intensity of physical activity during the measured period (Trost et al., 2011). A minimum wear time of 600 min/day was set. Non-wear periods were set with a minimum length of 60 min of consecutive zero-count epochs with up to 2 min of spike tolerance (Oliver et al., 2011). Evenson’s cut-off points were used to determine the percentage of time engaged in sedentary (0–100 counts/min), light physical activity (101–2295 counts/min) and MVPA variables (≥ 2296 counts/min) (Evenson et al., 2008). These mentioned criteria have been found to be the most valid cut-points within the adolescent population, according to the cross-validation study of Trost et al. (2011). In accordance with the above mentioned calibration studies, in the present study these cut points were calculated using the vertical axis. Data were analysed with the ActiLife Lifestyle Monitoring System Software version 6.13.2.

Weight status

Participants’ weight status was categorized as non-overweight and overweight/obese, according to the body mass index (BMI) international cut-off values (Cole et al., 2000). For this purpose, participants’ body weight and height were measured, and then the BMI was calculated (body weight/height squared, kg/m²). Weight and height were measured in shorts, T-shirts and barefoot. For the weight measure, the participant stood in the centre of the scale (Tanita HD 313, Arlington, IL, USA; accuracy = 0.1 kg) without support and with their weight distributed evenly on both feet. For the body height assessment, adolescents stood with their feet together with the heels, buttocks and upper part of the back touching the scale (SECA 206^®, Hamburg, Germany; accuracy = 0.1 cm), and with the head placed in the Frankfort plane. The average of two measurements for both weight and height were retained.

Procedures

The protocol of the present study was approved by The Ethical Committee of the University of Granada (reference number: 116). The principal and PE teacher of all school centres of the Community of Nuñoa were contacted by a researcher in order to inform them of the project and to ask for their permission to conduct this study. After the school approvals were obtained, students and their legal guardians were fully informed about all the features of the study and gave their consent to participate in this research.

All data collection was done during the months of July 2015 to October 2015. The first PE lesson was used for explaining the aim of the study, the confidentiality of the data and the rules to follow. Accelerometers were then placed above the right hip of the participants with an elastic band. Participants were asked to wear the accelerometer for seven days from waking to bedtime, and to take the accelerometer off only when engaged in aquatic activities or taking a shower. Students were also asked to continue with their normal activities during the week, and were encouraged to continue with organized sports activities. PE lessons were developed as usual, without any kind of intervention. Afterwards, two trained researchers conducted anthropometric measurements.

Statistical analyses

Descriptive statistics for the general characteristics and physical activity variables of the participants were calculated. A one-way analysis of variance was used to examine the potential differences between gender, age and weight status. Afterwards, the McNemar test was calculated for the whole sample in order to examine whether PE increased the proportion of adolescents achieving the daily recommendation of 60 min of MVPA (WHO, 2010). The Wilcoxon test was used to compare the physical activity levels between PE and non-PE days in the whole sample, as well as in gender, age and weight status categories. Additionally, the Mann–Whitney U test was used to examine the potential differences in physical activity levels between boys and girls, younger and older participants, and non-overweight and overweight participants. Adolescents’ age was categorized as younger (12–13 years) and older (14–15 years) and weight status was established as non-overweight (BMI < overweight cut-point) and overweight (BMI ≥ overweight cut-point (Cole et al., 2000)). To avoid potential bias due to differences in the length of total time of valid wear time in the variables sedentary, light physical activity and MVPA, time-based standardized scores (i.e. percentage of time) were used. All statistical analyses were performed using the SPSS Version 21.0 for Windows (IBM^® SPSS^® Statistics). The statistical significance level was set at p ≤ 0.05.

Results

From the initial sample of 156 adolescents who agreed to participate in the present study and met the inclusion criteria, 33 participants were eliminated due to meeting the exclusion criterion. Table 1 shows the general characteristics of the studied participants, as well as the differences between gender, age and weight status categories in terms of weight, height and BMI.

Table 1.

General characteristics (mean ± (standard deviation)) of the participants and differences between gender, age and weight status categories.

	Age, years	Weight, kg	Height, cm	BMI, kg/m²
Whole sample, N = 123	13.4 (0.7)	57.9 (10.9)	164.2 (7.5)	21.5 (3.5)
Boys, n = 71	13.5 (0.7)	59.3 (11.9)	167.1 (7.4)*	21.2 (3.5)
Girls, n = 52	13.3 (0.6)	56.1 (9.0)	160.2 (5.6)	21.8 (3.3)
Younger, n = 74^a	13.0 (0.2)	56.9 (10.2)	161.8 (7.0)*	21.7 (3.5)
Older, n = 49^a	14.1 (0.4)	59.6 (11.7)	167.7 (6.9)	21.1 (3.4)
Non-overweight, n = 87^b	13.5 (0.7)	53.3 (7.2)*	164.3 (7.4)	19.7 (1.9)*
Overweight, n = 36^b	13.2 (0.6)	69.3 (9.8)	163.8 (7.7)	25.8 (2.4)

^aAge categories were computed as younger (12–13 years) and older (14–15 years).

^bWeight status categories were established according to Cole et al. (2000) by BMI, age, and gender.

*p < 0.01 with the one-way analysis of variance for the boys–girls, younger–older, and non-overweight–overweight comparisons.

BMI: body mass index.

Whole sample

The McNemar test showed that there was a statistically significant difference between the proportions of adolescents achieving the daily recommendation of 60 min of MVPA on PE days and on non-PE days (23.6% and 14.6%, respectively; p ≤ 0.05). The Wilcoxon test results for all adolescents showed statistically significant greater values of MVPA, metabolic equivalents (METs) and vertical axis on PE days than on non-PE days (p < 0.05). However, for sedentary, light physical activity and steps variables, statistically significant differences between PE and non-PE days were not found (p > 0.05). Finally, statistically significant differences in terms of valid wear time between PE and non-PE days were not found (p > 0.05) (Table 2).

Table 2.

Comparison of adolescents’ objectively-measured physical activity levels between PE and non-PE days for the whole sample (N = 123).

	PE day	Non-PE day	Wilcoxon test
	M (Q₃–Q₁)	M (Q₃–Q₁)	95% CI	Z	p
Physical activity levels
Sedentary, minutes	798.0 (198.0)	805.0 (117.3)	(–2.12, 0.69)	1.083	0.279
Light, minutes	318.0 (116.0)	311.0 (96.0)	(–1.03, 1.21)	0.209	0.834
Moderate-to-vigorous, minutes	36.0 (39.0)	31.5 (29.8)	(0.12, 0.92)	2.529	0.011
Overall physical activity
METs	1.5 (0.2)	1.4 (0.2)	(0.00, 0.06)	2.198	0.028
Vertical axis, counts/min	290.8 (182.5)	269.3 (138.4)	(6.24, 51.67)	2.481	0.013
Steps, steps/min	8.4 (5.5)	7.7 (3.7)	(–0.14, 1.15)	1.545	0.122

PE: physical education; M: median; Q₃–Q₁: interquartile range; CI: confidence interval; MET: metabolic equivalent.

Tables 3, 4 and 5 show the results of the Wilcoxon and Mann–Whitney U tests regarding the participants’ gender, age and weight status, respectively.

Gender

Boys showed statistically significant greater values of MVPA and vertical axis on PE days than on non-PE days (p < 0.05), as well as showing greater values of MVPA and vertical axis than girls (p < 0.05) (Table 3).

Table 3.

Comparison of adolescents’ objectively-measured physical activity levels between PE and non-PE days for boys (n = 71) and girls (n = 52).

		PE day	Non-PE day	Wilcoxon test
		M (Q₃–Q₁)	M (Q₃–Q₁)	95% CI	Z	p
Physical activity levels
Sedentary, minutes	Boys	799.0 (237.0)	821.7 (148.0)	(–2.23, 1.69)	0.258	0.797
	Girls	795.5 (193.0)	796.6 (92.6)	(–3.35, 0.68)	1.503	0.133
Light, minutes	Boys	321.0 (132.0)	330.8 (112.3)	(–1.93, 0.99)	0.676	0.499
	Girls	312.5 (93.8)	296.8 (78.8)	(–0.80, 2.60)	1.147	0.251
Moderate-to-vigorous, minutes	Boys	40.0 (45.0)*	37.0 (30.9)**	(0.09, 1.35)	2.235	0.025
	Girls	29.0 (29.5)	22.0 (25.2)	(–0.14, 0.78)	1.348	0.178
Overall physical activity
METs	Boys	1.5 (0.3)	1.5 (0.2)*	(–0.01, 0.08)	1.507	0.132
	Girls	1.4 (0.2)	1.4 (0.2)	(–0.01, 0.07)	1.621	0.105
Vertical axis, counts/min	Boys	325.2 (216.8)*	293.6 (161.9)*	(0.67, 67.06)	2.023	0.043
	Girls	265.4 (167.9)	227.3 (114.5)	(–9.60, 52.24)	1.603	0.109
Steps, steps/min	Boys	8.7 (6.0)	8.0 (3.7)	(–0.45, 1.43)	0.943	0.346
	Girls	7.7 (4.1)	7.3 (3.4)	(–0.27, 1.41)	1.448	0.148

PE: physical education; M: median; Q₃–Q₁: interquartile range; CI: confidence interval; MET: metabolic equivalent.

*p < 0.05.

**p < 0.01 with the Mann–Whitney U test for the boys–girls comparisons.

Age

Older adolescents showed statistically significant greater values of MVPA and vertical axis on PE days than on non-PE days (p < 0.05), as well as showing a similar trend toward statistical significance in MET values (p = 0.058). However, for younger adolescents statistically significant differences were not found (p > 0.05) (Table 4).

Table 4.

Comparison of adolescents’ objectively-measured physical activity levels between PE and non-PE days for younger (n = 74) and older (n = 49) participants^a.

		PE day	Non-PE day	Wilcoxon test
		M (Q₃–Q₁)	M (Q₃–Q₁)	95% CI	Z	p
Physical activity levels
Sedentary, minutes	Younger	792.5 (186.8)	799.9 (136.4)	(–2.18, 1.40)	0.536	0.592
	Older	810.0 (226.5)	816.3 (112.3)	(–3.52, 1.21)	1.030	0.303
Light, minutes	Younger	307.5 (114.5)	308.5 (87.3)	(–1.47, 1.46)	0.040	0.968
	Older	320.0 (125.5)	320.5 (102.7)	(–2.03, 1.67)	0.274	0.784
Moderate-to-vigorous, minutes	Younger	34.5 (35.5)	28.4 (32.4)	(–0.12, 0.84)	1.471	0.141
	Older	39.0 (48.0)	33.0 (25.8)	(0.08, 1.49)	2.124	0.034
Overall physical activity
METs	Younger	1.5 (0.3)	1.5 (0.2)	(–0.01, 0.06)	1.288	0.198
	Older	1.5 (0.3)	1.4 (0.2)	(0.00, 0.09)	1.895	0.058
Vertical axis, counts/min	Younger	281.2 (172.4)	258.4 (142.8)	(–6.58, 49.48)	1.587	0.113
	Older	318.4 (186.0)	283.6 (125.7)	(0.08, 75.57)	1.965	0.049
Steps, steps/min	Younger	7.9 (5.2)	7.7 (3.7)	(–0.54, 1.09)	0.738	0.460
	Older	9.1 (5.4)	8.0 (3.6)	(–0.25, 1.94)	1.562	0.118

^aAge categories were computed as younger (12–13 years) and older (14–15 years).

PE: physical education; M: median; Q₃–Q₁: interquartile range; CI: confidence interval; MET: metabolic equivalent.

Weight status

Statistically significant differences between PE and non-PE days (p > 0.05) were not found for non-overweight nor overweight adolescents. However, it is worth mentioning that for non-overweight adolescents in MVPA, METs and vertical axis there was a trend toward statistical significance in favour of PE days (p = 0.055–0.064). Finally, regarding the between-group comparisons, results for both PE and non-PE days did not show any difference (Table 5).

Table 5.

Comparison of adolescents’ objectively-measured physical activity levels between PE and non-PE days for non-overweight (n = 87) and overweight (n = 36) participants^a.

		PE day	Non-PE day	Wilcoxon test
		M (Q₃–Q₁)	M (Q₃–Q₁)	95% CI	Z	p
Physical activity levels
Sedentary, minutes	Non-overweight	807.0 (174.0)	810.3 (153.4)	(–2.47, 0.55)	1.304	0.192
	Overweight	771.5 (244.5)	781.6 (92.9)	(–3.24, 2.97)	0.031	0.975
Light, minutes	Non-overweight	320.0 (106.0)	308.3 (88.3)	(–0.80, 1.70)	0.775	0.439
	Overweight	303.0 (162.5)	332.6 (100.4)	(–3.14, 1.59)	0.660	0.509
Moderate-to-vigorous, minutes	Non-overweight	35.0 (40.0)	28.8 (31.0)	(–0.03, 0.86)	1.852	0.064
	Overweight	37.5 (39.5)	35.5 (32.3)	(–0.16, 1.60)	1.665	0.096
Overall physical activity
METs	Non-overweight	1.5 (0.2)	1.4 (0.2)	(0.00, 0.06)	1.873	0.061
	Overweight	1.5 (0.3)	1.5 (0.2)	(–0.03, 0.10)	1.194	0.232
Vertical axis, counts/min	Non-overweight	285.2 (186.6)	253.2 (139.6)	(–0.53, 48.53)	1.917	0.055
	Overweight	325.8 (168.2)	294.3 (120.7)	(–14.85, 87.20)	1.587	0.113
Steps, steps/min	Non-overweight	8.2 (5.2)	7.5 (3.7)	(–0.31, 1.09)	1.143	0.253
	Overweight	8.9 (7.0)	8.1 (3.6)	(–0.70, 2.35)	1.021	0.307

PE: physical education; M: median; Q₃–Q₁: interquartile range; CI: confidence interval; MET: metabolic equivalent.

^aWeight status categories were established according to Cole et al. (2000) by body mass index, age and gender.

Discussion

The objectives of this study were: (a) to compare the grade of compliance with the daily recommendations of MVPA (60 min/day) in Chilean adolescents between PE days and non-PE days; and (b) to compare the physical activity levels between PE days and non-PE days, as well as the influence of gender, age and weight status.

Regarding the first objective, results showed that a greater percentage of Chilean adolescents achieved the daily recommendations of 60 min/day of MVPA on PE days than on non-PE days (23.6% vs. 14.6%, respectively). Although these results were in accordance with those carried out previously in different international contexts, the low percentage of adolescents achieving the daily recommendation by the WHO (2010) was even lower than in previous research (Cocca et al., 2014; Gao et al., 2011; Raustorp et al., 2010; Viciana et al., 2015). Results of this study were also lower when compared with those coming from self-reported measurements of the Chilean youth population (Chilean Ministry of Health/WHO, 2005; Muros et al., 2016). This is especially noteworthy considering that, as advised by Slootmaker et al. (2009), self-reported measurements usually obtain higher values than objective measurements of physical activity. For instance, in the study of Muros et al. (2016), with a sample of 515 Chilean children (with an average age of 10.6 years), 40 min of daily physical activity was registered with a self-reported measurement (Physical Activity Questionnaire for Children (Martínez-Gómez et al., 2009)). Moreover, results regarding physical activity in 8131 Chilean adolescents (Chilean Ministry of Health/WHO, 2005) showed that 14% of male and around 10% of female adolescents achieved the daily recommendations of physical activity, results similar to those obtained in the present study on non-PE days. Nevertheless, these two studies did not mention the differences between PE days and non-PE days. In the study carried out with pedometers by Moreno et al. (2015) with 250 children from the Nuñoa Community in Santiago, the authors detected a higher level of MVPA achieved (50 min/day for the whole sample, and with 33% of boys and 15% of girls accomplishing the recommendations) compared with the results of the present study. However, children evaluated in this study were 6–9 years old and the method of estimating the MVPA was different from the present study (pedometers vs. accelerometers). Results in the present study could verify a drop of MVPA levels from childhood on (Burrows et al., 2008), especially in these types of low-income neighbourhoods (Brusseau et al., 2011; Efrat, 2011; Elhakeem et al., 2015). In these areas, access to media equipment is easier and access to portable play equipment, such as a bicycle, is more difficult (Tandon et al., 2012). These results bring to light the necessity of implementing diverse programs focused on sports and general physical activity, especially during the leisure time of Chilean adolescents living in these kinds of neighbourhoods.

Regarding the second objective, the physical activity levels on PE days compared with non-PE days, as well as the influence of gender, age and weight status, results showed statistically greater values of MVPA for the whole sample during PE days (36 min) than for non-PE days (31.5 min). These results confirm the importance of PE classes and their contribution to reaching the recommended daily MVPA. Various authors verified this relevance in international contexts (Faulkner et al., 2014; Viciana et al., 2015; Yli-Piipari et al., 2016) and in younger Chilean students (Moreno et al., 2015). Moreover, PE classes have shown their effectiveness not only in the increment of daily MVPA, but also in contributing to other variables such as reducing body fat percentage in long-term interventions (Klakk et al., 2013).

Regarding gender, boys were more active during PE days than non-PE days, as well as being more active than girls on both days. Previous research found that for girls, the increment of MVPA is more influenced by non-structured periods during the day than structured periods, such as PE classes (Rushovich et al., 2006). This is more than likely the reason why girls were not statistically more active during PE days (although they were involved in seven minutes more MVPA during PE days than non-PE days). Perhaps, based on the link established between motivation toward PE and the MVPA in leisure time with adolescents (González-Cutre et al., 2014), increasing autonomous motivation in PE could be a good strategy for increasing the daily MVPA (on both PE and non-PE days) in female adolescents. Nevertheless, the complex inter-relationship between variables that influence habitual MVPA needs further research, particularly using objective measurements of physical activity and carried out with the Chilean population.

Regarding age, older Chilean adolescents were more active on PE days than non-PE days, which could signify that PE lessons help in maintaining the daily MVPA in this critical period of adolescence (Chilean Ministry of Health/WHO, 2005; Cocca et al., 2014). The fact that older adolescents were more active than younger adolescents could be explained by previous results obtained in similar contexts, where older participants were more responsible (and consequently more active) in structured periods, such as PE lessons, than younger ones (Viciana et al., 2016). Thus, it seems important to take this into consideration by promoting active periods for older adolescents directed by an expert adult (i.e. extracurricular sports activities) and focused on reaching higher levels of daily MVPA. ‘In continuation, it also seems that PE lessons should be likened to a more unstructured character for younger adolescents. For instance, creating PE lessons where students could decide the type of activity they perform, the sport modalities they practice, or even sharing the rules of the tasks and the grouping criteria in order to increase their enthusiasm and the intensity of their practice could be suggested.

Finally, weight status seemed not to be a crucial factor regarding the MVPA performed, according to the results obtained in this research. Studies with adolescents in international contexts have recognized the complex relationship between weight status and MVPA performed (Mayorga-Vega and Viciana, 2015; Viciana et al., 2016). For instance, Viciana et al. (2016) did not find a relationship between weight status and MVPA in school recess or PE periods, but did find a relationship in favour of overweight adolescents during leisure time, reporting reasons such as parental influences or socio-economic status as determinant factors. However, Mayorga-Vega and Viciana (2015) found, with 102 Spanish adolescents, statistically higher values of MVPA in PE, school recess and organized extra-curricular sports activities in favour of non-overweight adolescents. In Chilean youth, literature is still inconclusive regarding MVPA according to weight status. For instance, while Godard et al. (2012) found differences between overweight and non-overweight Chilean children, the study carried out by Moreno et al. (2015) did not. Nevertheless, it is necessary to go in-depth regarding the factor of weight status, especially in future research with Chilean adolescents. Moreover, results of this study should be interpreted with caution due to the research design used (ex-post-facto), which assumed that BMI could influence physical activity levels, although this relationship could also occur bidirectionally (Richmond et al., 2014).

The present study has shown that PE increases adolescents’ daily MVPA levels and, according to Martínez et al. (2012), this contribution is crucial for increasing weekly MVPA. The weekly contribution of PE could help in avoiding associated problems regarding the health of Chilean adolescents (overweight and obesity) and their consequences during adulthood (obesity and other chronic diseases) (Cañadas et al., 2014). However, results of the present study have shown a good but insufficient increment of time involved in MVPA for Chilean adolescents, in accordance with the previous research carried out by Martínez et al. (2012) and Viciana et al. (2015). Therefore, it seems important to stimulate the motivation of Chilean adolescents toward PE (in order to consequently increase the MVPA performed during lessons). Some strategies to apply in the Chilean PE context could be to increase certain psychological variables in the classes that mediate the performance of MVPA in adolescents (e.g. perception of competence (Barnett et al., 2008) or self-efficacy (Peinado et al., 2014)), and to increase the motor engagement time in the classes (i.e. through the task design or selecting appropriate organizational systems (Viciana et al., 2012)). Although increasing the number of PE sessions per week is also recommended, this does not depend on PE teachers or scientists (Viciana et al., 2015), but on politicians and their authority over the educational system.

Nevertheless, although the increment of MVPA during PE is internationally considered to be crucial regarding youth health (WHO, 2010), other educational objectives need to also be taken into account in the curriculum of PE for Chilean adolescents as mentioned by the Chilean Ministry of Education (2013) (e.g. alimentation care, or the psychological factors that influence the practice of physical activity and on the general wellbeing of school aged children).

The main points of strength of this study are the objectively-measured physical activity levels, as well as its being the first study with Chilean adolescents of these characteristics. Although accelerometer-based activity monitoring represents a significant advance in the area of physical activity assessment in field-based research, several authors have acknowledged the high non-compliance rate as one of the most important methodological issues (e.g. Howie and Straker, 2016; Trost et al., 2005). Recently, in a literature review by Howie and Straker (2016) it was found that in studies with children and adolescents that assessed physical activity through accelerometers the average non-compliance rate was 23%. Therefore, although in the present study the non-compliance rate could seem to be relatively high (i.e. 21%), it is common in this kind of study. However, this drop in the number of participants caused by the common loss of accelerometer data in these kinds of studies (Howie and Straker, 2016) did not allow for the examination, through a fully hierarchical analysis approach, of the influence of individual factors or overall interactions (e.g. physical activity of young overweight girls). These issues should be taken into account for future studies with a larger number of Chilean adolescents. Finally, the cross-sectional design does not allow for the inference of causal relationships.

Footnotes

Acknowledgements

The authors want to thank Aliisa Hatten for the English revision of the manuscript. Thank you to all the students and the Physical Education teachers who made this research possible.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

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