This is the published version of a paper published in Acta Paediatrica.
Citation for the original published paper (version of record):
Nyberg, G., Kjellenberg, K., Fröberg, A., Lindroos, A K. (2020)
A national survey showed low levels of physical activity in a representative sample of
Swedish adolescents.
Acta Paediatrica, 109(11): 2342-2353
https://doi.org/10.1111/apa.15251
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11 | INTRODUCTION
A large body of evidence demonstrates the benefits of physical ac-tivity (PA)1,2 and the negative consequences of sedentary behaviour3 for health among children and adolescents. PA recommendations
advocate children and adolescents accumulating at least 60 minutes of moderate-to-vigorous PA (MVPA) per day.4 In 2018, the second Swedish Report Card on Physical Activity for Children and Youth was published including 10 indicators of PA. Each indicator was graded, and the authors concluded that for the indicator total PA, depending
Received: 1 October 2019
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Revised: 6 February 2020|
Accepted: 10 March 2020DOI: 10.1111/apa.15251 R E G U L A R A R T I C L E
A national survey showed low levels of physical activity in a
representative sample of Swedish adolescents
Gisela Nyberg
1,2| Karin Kjellenberg
1,2| Andreas Fröberg
3| Anna Karin Lindroos
4,5This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
© 2020 The Authors. Acta Paediatrica published by John Wiley & Sons Ltd on behalf of Foundation Acta Paediatrica
1Department of Global Public Health,
Karolinska Institutet, Stockholm, Sweden
2The Swedish School of Sport and Health
Sciences, Stockholm, Sweden
3Department of Food and Nutrition and
Sport Science, University of Gothenburg, Gothenburg, Sweden
4Swedish Food Agency, Uppsala, Sweden
5Department of Internal Medicine and
Clinical Nutrition, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
Correspondence
Gisela Nyberg, Department of
Global Public Health , Karolinska Institute, Tomtebodavägen 18A, 171 77 Stockholm, Sweden.
Email: gisela.nyberg@ki.se Funding information Centrum for Idrottsforskning
Abstract
Aim: This study investigated objectively measured physical activity and
seden-tary time by sex, age and socioeconomic status in a large representative sample of Swedish adolescents.
Methods: In this cross-sectional national survey between 2016 and 2017, students
aged 11-12, 14-15 and 17-18 years from 131 schools were invited to participate. Physical activity and sedentary time were measured objectively with accelerometers for seven consecutive days. Socioeconomic status (parental education) and country of birth were self-reported in a questionnaire. Weight and height were measured by trained staff.
Results: A total of 3477 adolescents participated in the study, and 2419 (73%) had
at least 3 days of valid accelerometer data. The results showed that 43% of boys and 23% of girls reached the recommendation of 60 minutes of daily moderate-to-vig-orous physical activity. Boys were more physically active than girls in all age groups. Girls with high socioeconomic status were more physically active than girls with low socioeconomic status (P < .001), and this difference was not found in boys.
Conclusion: The majority of Swedish adolescents did not reach the physical
activ-ity recommendation, and boys were more active than girls. Effective strategies to increase physical activity, especially among girls with low socioeconomic status, are urgently needed.
K E Y W O R D S
accelerometry, physical activity recommendation, school, sedentary time, socioeconomic status
on sex and age, approximately 18%-43% of Swedish children and 33%-46% of Swedish adolescents reach to the PA recommenda-tions.5 Although PA was measured objectively with accelerometry, the studies which supported these conclusions were based on small samples of 343 children and 140 adolescents.5,6 Furthermore, the Public Health Agency of Sweden recently showed that children aged 11, 13 and 15 years (n = 426) spent 67%-75% of their time awake sedentary.7
Thus, there is a lack of population-based representative Swedish studies using objective measures such as accelerometers to investi-gate PA and sedentary time.5,6 Studies with representative data on objectively measured PA and sedentary time are needed to provide researchers, policy makers, and various stakeholders with an accu-rate and reliable basis for identifying problem areas related to PA and sedentary time. Such studies also provide reference data on ob-jectively measured PA and sedentary time and make it possible to identify potential risk groups with low levels of PA and high levels of sedentary time, groups for which appropriate intervention strategies need to be developed.
The aim of the present study was to investigate objectively mea-sured PA and sedentary time by sex, age and socioeconomic status (SES) in a large representative sample of Swedish adolescents. This is the first national study in Sweden with objective measurements of PA and sedentary time in a representative sample of 11- to 18-y-olds.
2 | METHODS
2.1 | Recruitment
This study was part of a large national representative cross-sectional dietary survey, Riksmaten Adolescents 2016-17, conducted by the Swedish Food Agency.
A total of 619 schools were selected by Statistics Sweden based on type of municipality, school organisation (public or independent) and geographical location. Of these schools, 601 schools were in-vited and 131 schools took part. The schools selected 1-2 classes in a given school grade, in the age groups 11-12, 14-15 or 17-18 years. All students, in the selected classes, were invited to participate in the study, and 3477 students participated in at least one part of the survey. The participants were representative of the population with regard to socioeconomic background and school organisation. Furthermore, all types of municipalities were represented and over-all, the geographic distribution corresponded satisfactory to the underlying population.8 The study design, methods and participa-tion are described in more detail elsewhere.8 Information letters were sent to the students and their guardians three weeks before staff from the Swedish Food Agency planned to visit the school. In the subgroup providing blood and urine, not used in the present study, written consent was required from the participants and also from the parents if the participants were younger than 16 years. In schools not subject to biological sampling, an opt-out consent was used.8 Staff from the Swedish Food Agency visited the schools
during school hours to inform the students about the study and to collect data, height and weight, questionnaires, dietary intake using a web-based method, and PA and sedentary time using accelerome-ters. The data collection was carried out between September 2016 and May 2017 to account for seasonal differences. Ethical approval was obtained from the Regional Ethical Review Board in Uppsala, Sweden (No. 2015/190).
2.2 | Data collection
2.2.1 | Anthropometry
Height and weight were measured in light clothing, by trained staff, using standardised methods in schools. Weight was measured with the digital scales SECA 862 or 899 (SECA Weighing and Measuring Systems) to the nearest 0.1 kg, and height was measured to the nearest 0.1 cm using the portable stadiometer SECA 213 (SECA Weighing and Measuring Systems). Body mass index was calculated (kg/m2) and weight status was defined according to the International Obesity Task Force recommendations.9
2.2.2 | Physical activity and sedentary time
Physical activity and sedentary time were objectively measured using tri-axial accelerometers from ActiGraph models GT3X and GT3X+ (Actigraph LLC). The accelerometers were distributed by the staff from the Swedish Food Agency during the school visit. The participants were instructed to wear the accelerometer around the waist using an elastic belt with the monitor placed on the right hip for 7 consecutive days at all times when awake, except during water-related activities. After the accelerometer had been worn for 7 days, the class teacher collected the monitors and sent them back to the staff at the Swedish Food Agency in a prepaid envelope. The moni-tors were set to collect data at 5-second epoch time intervals at a sample rate of 30 Hertz.
The accelerometer data were processed using ActiLife version 6.13.3. Non-wear time was removed, defined as time periods of at
Key notes
• For the first time in Sweden, physical activity (PA) and sedentary time have been objectively measured in a large nationally representative sample of adolescents and refer-ence values for age groups of adolescent boys and girls are provided.
• The majority of adolescents did not reach the PA recom-mendation, and boys were more active than girls.
• Effective strategies to increase PA, especially among girls with low socioeconomic status, are urgently needed.
least 60 consecutive minutes of zero counts, with zero-minute spike tolerance. A valid day was defined as ≥500 minutes, 8.3 hours, of wear time. A time filter was set between 06:00 and 22:59 for those aged 12 and 15 years and 06:00 and 23:59 for those aged 18 years. To analyse PA during school time, a separate time filter was set be-tween 08:00 and 15:59 during weekdays and the same filter was used across all ages.
Mean total PA was estimated in two versions: (a) the sum of the vertical axis activity counts divided by recorded minutes, vertical axis counts per minute (CPM) and (b) the square root of the sum of activity counts squared in each vector, vector magnitude divided by recorded minutes. Descriptive data for both CPM vertical axis and CPM vector magnitude are presented in Table 2. In further analyses of total PA, CPM vertical axisv is used. In addition, cut-points were used to estimate sedentary time (≤100 CPM), light PA (101-2295 CPM), moderate PA (MPA) (2296-4011 CPM), vigorous PA (VPA) (≥4012 CPM) and MVPA (≥2296 CPM).10,11 Only participants with at least 3 valid days, 2 weekdays and 1 weekend day, were included in the weekly analyses. A minimum of 1 valid day was required for the analyses of weekdays and weekend days. The weekly average of ≥60 minutes of MVPA per day was used in order to categorise the participants into reaching or not reaching the physical activity recommendation.
2.2.3 | Background information
Parental educational background was reported by the participants' parents and used as a proxy for SES. The highest level of education attained by either parent was used, and the answers were dichot-omised into low SES if the highest education was ≤12 years and high SES if the highest education was >12 years of schooling.
The municipalities were categorised into one of five groups based on the Swedish municipality classification 2011. The first three groups were metropolitan municipalities, suburbs surround-ing metropolitan areas and large cities and surroundsurround-ing suburbs, and these groups were categorised as urban areas. The two other groups were densely populated municipalities, and other municipalities such as commuter municipalities, tourism and travel industry municipal-ities, manufacturing municipalmunicipal-ities, sparsely populated municipali-ties and municipalimunicipali-ties in sparsely populated regions, and these two groups were categorised as urban areas.8
The country of birth was reported by the participant, and the answers were dichotomised into Sweden or outside Sweden.
2.2.4 | Statistics
All the analyses were cross-sectional. Data analyses were performed using IBM SPSS Statistics for Windows, Version 24.0. (IBM Corp) and Statistica version13.2 (Statsoft, Inc.). Descriptive statistics are pre-sented as means, standard deviations and proportions. Independent
samples t test was used for continuous data and chi-square test for categorical data to test for differences between sex, age groups and SES. Analysis of variance was used to examine the weekly pattern in mean total PA across days and the difference between weekdays and weekends in total PA, sedentary time, moderate PA, vigorous PA and MVPA. Analysis of variance was also used to examine differ-ences in total PA, MVPA and sedentary time by SES, type of munici-pality and country of birth by adjusting for these variables and age in the same model. Mean values of PA and sedentary time variables were similar when schools were included as a cluster in the statistical analyses. School cluster was therefore not included as a co-variate in the analyses. The level of statistical significance was set at P < .05.
3 | RESULTS
The descriptive characteristics of the participants are shown in Table 1. In total, 3477 children (53% girls) were included in the study. A total of 39% of the parents had low SES, 68% reported that they lived in an urban area and 88% were born in Sweden. The prevalence of overweight and obesity was 21% in the total sample.
3.1 | Physical activity by age groups and sex
As shown in Figure 1, a total of 3302 participants wore the accel-erometers, 3246 had at least 1 day of valid registration, 2419 par-ticipants (73%) had at least 3 days of valid registrations, including at least 1 weekend day, and 1220 participants had 7 days of valid reg-istrations. The drop-out analyses showed that more girls (P < .001), younger participants (P < .001) and participants with high SES (P < .001) wore the accelerometers for at least 3 days. There was no difference in terms of overweight status. The mean (SD) wear time was 808 (78) minutes for the whole week with no significant difference between boys and girls. However, girls had more wear time in the total sample during weekdays compared to boys. The re-sults from the objective measurements of PA and sedentary time are shown in Table 2.
3.2 | Proportions reaching the physical activity
recommendation
A total of 32% (95% CI: 30-34) of the whole sample, 43% (95% CI: 40-46) of the boys and 23% (95% CI: 21-26) of the girls (P < .001), reached the PA recommendation (shown in Figure 2). The sex dif-ference was also statistically significant within each age group. The proportion of boys and girls that reached the PA recommendation was 54% (95% CI: 49-58) and 32% (95% CI: 28-36) in the age group 11-12 years (P < .001), 39% (95% CI: 34-43) and 17% (95% CI: 13-21) in the age group 14-15 years (P < .001), and 31% (95% CI: 26-36) and 20% (95% CI: 16-24) in the age group17-18 years (P = .002).
T A B LE 1 D es cr ip tiv e c ha ra ct er is tic s c at eg or is ed b y s ex a nd a ge g ro up s A ll 11 -1 2 y 14 -1 5 y 17 -1 8 y To ta l B oy s G irl s To ta l B oy s G irl s To ta l B oy s G irl s To ta l B oy s G irl s N um be r 347 7 16 35 18 42 12 17 59 5 62 2 11 98 573 62 5 10 62 467 59 5 A ge ( y) ( M ea n [ SD ]) (n = 3 47 5) 14 .4 (2 .6 ) 14 .4 (2 .5 ) 14 .5 (2 .6 ) 11 .5 (0 .4 ) 11 .5 (0 .4 ) 11 .5 (0 .4 ) 14 .5 (0 .4 ) 14 .5 (0 .4 ) 14 .5 (0 .4 ) 17 .7 (0 .7 ) 17. 8 ( 0. 7) 17. 7 ( 0. 6) H ig h S ES ( % ) (n = 3 04 7) 61 60 62 62 60 64 63 60 65 57 58 56 C ou nt ry o f b ir th , Sw ed en ( % ) (n = 3 43 8) 88 87 89 90 89 91 87 85 88 87 86 88 Ty pe o f m un ic ip al ity , ur ba n ( % ) ( n = 34 77 ) 68 71 66 71 73 68 75 72 77 58 65 53 B od y m as s i nd ex c at eg or ie s a (n = 3 44 3) U nd er w ei gh t ( %) b 7 6 7 8 7 9 7 6 7 5 5 5 N or mal w ei gh t ( % ) b 72 72 72 70 71 68 75 75 76 71 68 72 O ve rw ei gh t (% ) b 17 17 17 18 18 18 15 15 15 19 20 18 O be se ( % ) b 4 5 4 4 4 4 4 5 3 6 7 4 aD ef in ed a cc or di ng t o t he I nt er na tio na l O be si ty T as k F or ce . bTo ta ls m ay n ot a dd u p d ue t o r ou nd in g.
3.3 | Whole week
There were significant differences in all PA variables and seden-tary time between age groups (all P < .001). Those in the age group 11-12 years had higher PA and lower sedentary time than those in the two older age groups. Similarly, those in the age group 14-15 years had higher PA and lower sedentary time than those in the oldest age group.
Boys had significantly higher total PA compared to girls in the whole sample (456 vs 398 cpm, P < .001) and in all age groups as shown in Table 2.
Boys had less sedentary time (3%) and spent more time in light PA (7%), moderate PA (14%), vigorous PA (24%) and MVPA (18%) compared to girls in the whole sample, shown in Table 2. Within age groups, in the age group 11-12 years, there were significant differ-ences between boys and girls in moderate PA (37 vs 32 minutes, P < .001), vigorous PA (26 vs 22 minutes, P < .001) and MVPA (64 vs 54 minutes, P < .001). There were differences in the age group 14-15 years in sedentary time (613 vs 644 minutes, P < .001), light
PA (133 vs 122 minutes, P < .001), moderate PA (29 vs 26 minutes, P < .001), vigorous PA (25 vs 20 minutes, P < .001) and MVPA (55 vs 46 minutes, P < .001) and in the age group 17-18 years, in vigor-ous PA (25 vs 22 minutes, P = .008) and MVPA (51 vs 46 minutes, P = .010).
3.4 | Weekdays and weekends
Total PA was significantly higher during weekdays compared to weekends in the whole sample (P < .001). Boys had significantly higher total PA compared to girls in the whole sample (478 vs 406 cpm, P < .001) and in all age groups during weekdays and in the whole sample (415 vs 374 cpm, P < .001) and in the age group 14-15 years during weekends shown in Figure 3.
Sedentary time was significantly higher (8%) and light PA (7%), moderate PA (29%), vigorous PA (39%) and MVPA (33%) significantly higher during weekdays compared to weekends in the whole sample (P < .001), shown in Table 2.
T A B LE 2 O bj ec tiv el y m ea su re d s ed en ta ry t im e a nd p hy si ca l a ct iv ity a m on g b oy s a nd g irl s, s tr at ifi ed b y a ge g ro up s A ll 11 -1 2 y 14 -1 5 y 17 -1 8 y To ta l M ea n (S D) B oy s M ean (S D) G irl s M ean (S D) P To ta l M ean (S D) B oy s M ea n ( SD ) G irl s M ean (S D) P To ta l M ean (S D) B oy s M ean (S D) G irl s M ean (S D) P To ta l M ean (S D) B oy s M ean (S D) G irl s M ean (S D) P W hole w ee k n = 24 19 n = 10 34 n = 13 85 n = 94 8 n = 44 7 n = 50 1 n = 80 5 n = 33 8 n = 46 7 n = 66 6 n = 24 9 n = 41 7 W ea r t im e, min /d 808 (7 8) 80 6 ( 80 ) 80 9 ( 75 ) .37 0 808 (7 4) 81 0 ( 76) 80 5 ( 71 ) .3 34 807 (7 8) 80 0 ( 82 ) 81 2 ( 75 ) .0 3 810 (8 2) 80 9 ( 84 ) 81 1 ( 81 ) .76 1 To ta l P A , C PM v 42 3 (1 68 ) 45 6 (17 7) 39 8 (1 57 ) <. 00 1 50 0 (17 5) 51 9 (17 2) 48 2 (17 5) <. 00 1 38 7 ( 14 0) 42 9 (1 58 ) 35 7 (1 17 ) <. 00 1 35 6 ( 14 6) 37 8 (17 0) 34 3 (1 28 ) .0 03 To ta l P A , C PM vm 76 1 ( 269) 821 (2 92 ) 71 6 ( 241 ) <. 00 1 937 (2 54 ) 97 9 ( 26 4) 89 8 ( 239 ) <. 00 1 69 1 ( 20 8) 759 (2 39 ) 641 (1 67 ) <. 00 1 59 7 ( 20 4) 62 1 ( 247 ) 58 2 (17 2) .0 17 Se den ta ry time , min /d 61 9 ( 83 ) 607 (8 6) 62 8 ( 80 ) <. 00 1 58 2 ( 73 ) 57 8 ( 76 ) 58 5 ( 71 ) .14 9 63 1 (7 6) 61 3 ( 79 ) 64 4 ( 72 ) <. 00 1 657 (8 2) 65 2 ( 91) 66 0 ( 76 ) .19 6 Li gh t P A , min /d 13 6 ( 39) 14 2 ( 40 ) 13 3 ( 38 ) <. 00 1 16 7 ( 31 ) 16 8 ( 32 ) 16 6 ( 29 ) .47 1 12 6 (2 9) 13 3 ( 33 ) 12 2 (2 6) <. 00 1 10 5 ( 28 ) 10 7 ( 29 ) 10 4 ( 27 ) .3 48 Mo der at e PA , min /d 30 (11 ) 32 (1 3) 28 (9) <. 00 1 35 (1 0) 37 (11 ) 32 ( 8) <. 00 1 28 (1 0) 29 (1 2) 26 (9) <. 00 1 25 (11 ) 26 (1 3) 25 (1 0) .19 3 V ig or ou s PA , min /d 23 (1 3) 26 (14 ) 21 (1 2) <. 00 1 24 (1 2) 26 (1 3) 22 (11 ) <. 00 1 22 (1 3) 25 (14 ) 20 (11 ) <. 00 1 23 (1 5) 25 (1 6) 22 (1 5) .0 08 MVP A , min /d 53 (21 ) 58 ( 23 ) 49 (18 ) <. 00 1 59 (2 0) 64 (21 ) 54 (17 ) <. 00 1 50 (19 ) 55 (2 2) 46 (1 6) <. 00 1 48 (21 ) 51 (2 4) 46 (19 ) .0 10 We ek da ys n = 32 43 n = 14 92 n = 17 51 n = 11 62 n = 56 4 n = 59 8 n = 11 02 n = 51 3 n = 58 9 n = 97 9 n = 41 5 n = 56 4 W ea r t im e, min /d 80 9 ( 95 ) 79 8 (1 03 ) 818 (8 6) <. 00 1 813 (8 3) 811 (8 9) 81 5 ( 76) .3 10 80 8 ( 96) 79 3 (1 02 ) 82 2 ( 88 ) <. 00 1 80 5 (1 06 ) 78 9 ( 119 ) 818 (9 3) <. 00 1 To ta l P A , C PM v 43 9 (17 0) 47 8 (17 9) 40 6 (1 54 ) <. 00 1 51 5 (17 0) 54 4 ( 169) 48 8 (1 68 ) <. 00 1 417 (1 54 ) 46 7 (17 0) 37 3 (1 22 ) <. 00 1 37 3 ( 151 ) 40 1 ( 16 9) 35 3 (1 33 ) <. 00 1 To ta l P A , C PM vm 77 9 ( 28 0) 85 0 ( 30 3) 71 8 ( 24 3) <. 00 1 96 7 ( 26 0) 103 0 ( 268 ) 90 8 ( 23 8) <. 00 1 731 (2 34 ) 817 (2 63 ) 65 7 (17 4) <. 00 1 60 9 ( 211 ) 64 8 ( 24 6) 58 0 (17 6) <. 00 1 Se den ta ry time , min /d 618 (9 3) 598 (98 ) 63 5 ( 86) <. 00 1 58 0 ( 78 ) 57 0 ( 83 ) 59 0 ( 72 ) <. 00 1 62 5 ( 90) 59 8 ( 93 ) 649 (8 0) <. 00 1 65 4 ( 98 ) 63 5 ( 11 0) 66 8 (8 5) <. 00 1 Li gh t P A , min /d 13 5 ( 43 ) 14 0 ( 45 ) 131 (4 0) <. 00 1 17 0 ( 33 ) 17 3 (3 4) 16 8 ( 32 ) .020 12 9 ( 32 ) 135 (35 ) 123 (28 ) <. 00 1 10 0 ( 29 ) 10 0 ( 32 ) 10 0 ( 26 ) .9 44 Mo der at e PA , min /d 31 (1 2) 33 (1 3) 30 (1 0) <. 00 1 37 (11 ) 40 (1 2) 34 (9) <. 00 1 30 (11 ) 32 (1 2) 28 (1 0) <. 00 1 26 (11 ) 26 (1 2) 27 (11 ) .7 78 V ig or ou s PA , min /d 25 (14 ) 28 (1 5) 22 (1 3) <. 00 1 26 (1 2) 28 (1 3) 23 (11 ) <. 00 1 24 (14 ) 27 (1 5) 21 (1 2) <. 00 1 25 (17 ) 27 (1 8) 23 (1 6) <. 00 1 MVP A , min /d 56 ( 22 ) 61 (2 4) 52 (19 ) <. 00 1 62 (21 ) 68 ( 22 ) 57 (1 8) <. 00 1 54 (21 ) 59 (2 3) 49 (18 ) <. 00 1 51 (2 2) 54 (24 ) 49 (2 0) .0 04
T A B LE 2 (Co nti nue d) A ll 11 -1 2 y 14 -1 5 y 17 -1 8 y To ta l M ea n (S D) B oy s M ean (S D) G irl s M ean (S D) P To ta l M ean (S D) B oy s M ea n ( SD ) G irl s M ean (S D) P To ta l M ean (S D) B oy s M ean (S D) G irl s M ean (S D) P To ta l M ean (S D) B oy s M ean (S D) G irl s M ean (S D) P W eek en d d ay s n = 24 39 n = 10 48 n = 13 91 n = 95 0 n = 44 8 n = 50 2 n = 81 2 n = 34 3 n = 46 9 n = 67 7 n = 25 7 n = 42 0 W ea r t im e, min /d 74 1 ( 12 3) 74 0 ( 12 7) 74 1 ( 12 0) .8 93 751 (1 23 ) 75 3 (1 31 ) 74 9 ( 11 5) .638 732 (1 23 ) 73 0 (1 22 ) 73 4 (1 24 ) .6 05 73 7 (1 23 ) 73 3 (1 24 ) 73 9 (1 22 ) .52 6 To ta l P A , C PM v 39 2 ( 261 ) 41 5 ( 28 6) 374 (2 39 ) <. 00 1 476 (2 96 ) 481 (3 08 ) 47 1 ( 28 6) .61 9 34 4 ( 218 ) 37 9 ( 25 5) 319 (1 84 ) <. 00 1 33 1 ( 22 0) 34 8 ( 26 0) 32 0 ( 190) .11 3 To ta l P A , C PM vm 72 4 (3 73 ) 75 7 ( 41 5) 70 0 ( 337 ) <. 00 1 88 6 (4 00 ) 89 6 ( 42 8) 87 7 ( 37 3) .4 82 63 9 ( 311 ) 690 (3 60) 60 2 ( 26 3) <. 00 1 60 0 ( 318 ) 60 7 (3 84 ) 59 6 ( 27 1) .6 67 Se den ta ry time , min /d 57 3 (1 17 ) 56 9 (1 21 ) 57 5 ( 11 3) .17 7 55 2 ( 11 5) 55 5 ( 12 1) 55 0 ( 11 0) .5 01 58 1 (1 17 ) 57 2 ( 119 ) 58 8 ( 11 5) .0 53 59 1 ( 114 ) 59 0 (1 22 ) 59 2 ( 10 9) .7 97 Li gh t P A , min /d 12 6 ( 47 ) 12 6 ( 49) 12 6 ( 46) .7 33 15 0 (4 3) 14 6 ( 47 ) 15 4 ( 38 ) .0 08 11 3 ( 41 ) 11 7 ( 44 ) 111 (3 8) .0 67 10 8 ( 47 ) 10 2 ( 46 ) 111 (4 8) .02 2 Mo der at e PA , min /d 24 (1 5) 26 (17 ) 23 (1 3) <. 00 1 29 (1 5) 30 (1 6) 27 (1 2) .0 01 22 (14 ) 23 (1 5) 21 (1 3) .0 71 21 (1 5) 22 (1 8) 20 (1 3) .0 49 V ig or ou s PA , min /d 18 (17 ) 20 (19 ) 16 (1 5) <. 00 1 20 (1 6) 21 (1 8) 18 (14 ) .0 07 16 (17 ) 19 (2 0) 14 (1 5) <. 00 1 17 (1 9) 18 (2 1) 16 (17 ) .1 21 MVP A , min /d 42 (2 9) 46 ( 32 ) 39 ( 25 ) <. 00 1 48 ( 28 ) 52 (3 1) 46 (24 ) .0 01 38 (27 ) 42 (3 1) 35 (24 ) .0 01 38 ( 30 ) 40 ( 35 ) 36 (2 6) .0 45 Sch oo l t im e n = 33 02 n = 15 39 n = 17 63 n = 11 70 n = 57 1 n = 59 9 n = 11 24 n = 53 1 n = 59 3 n = 11 08 n = 43 7 n = 57 1 W ea r t im e, min /d 41 8 ( 68 ) 41 0 ( 75 ) 42 5 (6 2) <. 00 1 43 5 ( 55 ) 43 0 (5 8) 44 0 ( 51 ) <. 00 1 41 6 ( 71 ) 40 9 ( 77 ) 42 3 (6 6) <. 00 1 40 0 ( 75 ) 38 5 ( 86) 41 0 ( 65 ) <. 00 1 Se den ta ry time , min /d 31 2 ( 61 ) 295 (6 5) 32 6 (5 4) <. 00 1 30 0 ( 47 ) 287 (5 0) 31 2 (4 0) <. 00 1 316 (6 5) 29 7 (6 8) 33 2 (5 8) <. 00 1 321 (7 0) 30 3 ( 77 ) 33 5 ( 60) <. 00 1 MVP A , min /d 31 (1 3) 34 (14 ) 29 (11 ) <. 00 1 36 (1 3) 40 (14 ) 33 (1 0) <. 00 1 29 (1 3) 32 (1 3) 27 (11 ) <. 00 1 27 (1 2) 27 (1 2) 26 (11 ) .3 21 Lei su re tim e n = 32 43 n = 14 92 n = 17 51 n = 11 62 n = 56 4 n = 59 8 n = 11 02 n = 51 3 n = 58 9 n = 97 9 n = 41 5 n = 56 4 W ea r t im e, min /d 39 1 ( 88) 38 8 ( 97 ) 394 (8 0) .0 6 37 8 ( 80 ) 38 0 (8 5) 376 (7 5) .3 13 392 (8 8) 38 4 ( 99) 39 9 ( 77 ) .0 05 40 6 (94 ) 40 3 (1 06 ) 40 8 ( 84 ) .47 8 Se den ta ry time , min /d 281 (7 7) 271 (8 4) 28 9 ( 70 ) <. 00 1 26 3 (6 6) 26 2 ( 71 ) 26 4 (6 2) .62 2 28 3 ( 74 ) 26 8 ( 79) 29 6 ( 67 ) <. 00 1 29 9 ( 88 ) 28 8 (1 02 ) 30 8 ( 75 ) .0 01 MVP A , min /d 23 (14 ) 24 (1 5) 22 (1 2) <. 00 1 24 (1 2) 25 (1 3) 23 (11 ) .0 05 22 (14 ) 23 (1 5) 21 (1 2) .0 02 22 (1 5) 23 (1 8) 21 (1 3) .0 62 A bb rev iat io ns : C PM v , c ou nt s p er m in ut e (v er tic al ); C PM vm , c ou nt s p er m in ut e ( ve ct or m ag ni tu de ); M V PA , m oder at e-to -vi go ro us p hy si ca l ac tiv ity ; P A , p hy si ca l ac tiv ity ; SD , s ta nd ar d de vi at io n.
Boys had less sedentary time (598 vs 635 minutes, P < .001) and spent more time in light PA (140 vs 131 minutes, P < .001), moder-ate PA (33 vs 30 minutes, P < .001), vigorous PA (28 vs 22 minutes, P < .001) and MVPA (61 vs 52 minutes, P < .001) compared to girls in the whole sample during weekdays and in all age groups except for light PA and moderate PA in the age group 17-18 years.
During the weekends, the boys had more time in moderate PA (26 vs 23 minutes, P < .001), vigorous PA (20 vs 16 minutes, P < .001) and MVPA (46 vs 39 minutes, P < .001) than girls in the whole sample. Within age groups, in the age group 11-12 years, boys spent less time than girls in light PA (146 vs 154 minutes, P = .008) but more time in moderate PA (30 vs 27 minutes, P = .001), vigorous PA (21 vs 18 min-utes, P = .007) and MVPA (52 vs 46 minmin-utes, P = .001). In the age group 14-15 years, boys spent more time in vigorous PA (19 vs 14 minutes, P < .001) and MVPA (42 vs 35 minutes, P = .001) than girls and in the age group 17-18 years, and boys spent less time in light PA (102 vs 111 minutes, P = .02) but more time in moderate PA (22 vs 20 minutes, P = .049) and MVPA (40 vs 36 minutes, P = .045) than girls.
3.5 | School time and leisure time
In the total sample, on average 31 minutes were spent in MVPA per day during school time compared to 23 minutes during leisure time, shown in Figure 4 and Table 2. There were significant differences between boys and girls during both school time (P < .001) and lei-sure time (P < .001) where boys had less sedentary time (11%) and more time in MVPA (17%) than girls. Likewise, sedentary time during school time differed significantly in all the age groups (P < .001) and MVPA in all age groups except age group 17-18 years (P < .001).
During leisure time, there were significant differences between boys and girls in the age group 11-12 years for MVPA (25 vs 23 min-utes, P = .005), in the age group 14-15 years for sedentary time (268 vs 296 minutes, P < .001) and MVPA (23 vs 21 minutes, P = .002) and
in the age group 17-18 years, for sedentary time (288 vs 308 min-utes, P = .001).
3.6 | Socioeconomic status, type of municipality and
country of birth
Differences in SES, type of municipality and country of birth were studied for the variables total PA, MVPA and sedentary time for boys and girls separately.
The descriptive results from the objective measurements of PA and sedentary time stratified by SES are shown in Table 3.
The adjusted analyses revealed that girls with high SES had higher total PA (388 vs 360 counts per minute, P = .001) and MVPA (49 vs 46 minutes, P < .001) compared to girls with low SES, but there was no difference in sedentary time. No significant differences were found between boys with high and low SES in total PA, MVPA and sedentary time.
Girls in urban areas had lower sedentary time compared to girls living in rural areas (638 vs 650 minutes, P = .007), but there were no differences in total PA and MVPA. No significant differences in total PA, MVPA and sedentary time were found between boys living in urban areas vs rural areas.
Girls born in Sweden had higher total PA (392 vs 356 counts per minute, P = .01) and lower sedentary time (629 vs 659 minutes, P < .001) than girls born outside Sweden. No significant differences in total PA, MVPA and sedentary time were found between boys born in Sweden and outside of Sweden.
4 | DISCUSSION
This is the first Swedish nationwide study in which the PA and sed-entary time of a representative sample of adolescents have been examined with objective measurements. The results showed that a
F I G U R E 3 Total physical activity by sex, age group and type of
day (weekdays: 11-12 y: boys n = 564, girls n = 598; 14-15 y: boys n = 513, girls n = 589; 17-18 y: boys n = 415 , girls n = 564, weekends: 11-12 years: boys n=448, girls n=502; 14-15 years: boys n=343, girls n=469; 17-18 years: boys n=257, girls n=420 ) presented as means with 95% confidence intervals
0 100 200 300 400 500 600 11-12 y 14-15 y 17-18 y 11-12 y 14-15 y 17-18 y d n e k e e W s y a d k e e W
Counts per minute (CPM)
Boys Girls
F I G U R E 2 Participants meeting the physical activity
recommendation (%) by sex and age group (11-12 y, boys n = 447, girls n = 501, 14-15 y, boys n = 338, girls n = 467, and 17-18 y, boys n = 249, girls n = 417) presented as means with 95% confidence intervals 0 10 20 30 40 50 60 11-12 y 14-15 y 17-18 y
Percent meeting the
PA
recommendation
T A B LE 3 O bj ec tiv el y m ea su re d s ed en ta ry t im e a nd p hy si ca l a ct iv ity a m on g b oy s a nd g irl s a cc or di ng t o s oc io ec on om ic s ta tu s ( SE S) , t ot al s tu dy p op ul at io n a nd s tr at ifi ed b y a ge g ro up s To ta l M ea n ( SD ) B oy s M ea n ( SD ) G irl s M ea n ( SD ) H ig h S ES Lo w S ES P H ig h S ES Lo w S ES P H ig h S ES Lo w S ES P A ll Whole w ee k n = 14 05 n = 83 1 n = 57 0 n = 35 4 n = 83 5 n = 47 7 To ta l P A , C PM v 42 8 (1 69 ) 40 9 (1 64 ) .0 11 45 4 (17 8) 45 2 (1 71 ) .88 4 41 0 ( 16 0) 37 7 (1 52 ) <. 00 1 To ta l P A , C PM vm 76 3 ( 26 6) 74 8 ( 26 8) .1 92 812 (2 88 ) 82 3 ( 28 9) .5 49 73 0 ( 24 6) 69 2 ( 23 7) .0 06 Se den ta ry ti me , m in /d 62 1 ( 79 ) 62 0 ( 87 ) .7 23 61 1 ( 81 ) 60 6 ( 87 ) .4 30 62 8 ( 76 ) 629 (8 5) .71 2 Li gh t P A , m in /d 13 5 ( 38 ) 13 8 ( 40 ) .1 35 13 9 ( 39 ) 14 6 ( 43 ) .0 19 13 3 (3 8) 13 2 ( 38 ) .8 00 M od er ate P A , m in/ d 30 (11 ) 29 (1 2) .969 31 (1 2) 33 (1 3) .17 3 28 (9) 27 (1 0) .0 69 V ig or ous P A , min /d 24 (1 3) 21 (1 2) <. 00 1 26 (14 ) 25 (1 2) .07 9 22 (1 2) 19 (1 2) <. 00 1 M V PA , min /d 53 ( 20 ) 51 (2 0) .0 06 58 ( 23 ) 57 (2 1) .75 0 51 (17 ) 46 (1 8) <. 00 1 11 -1 2 y W hole w ee k n = 55 1 n = 32 3 n = 24 5 n = 15 5 n = 30 6 n = 16 8 To ta l P A , C PM v 50 7 (17 8) 49 2 (17 3) .2 05 52 0 (17 5) 52 5 (17 2) .7 78 49 7 ( 181 ) 461 (1 68 ) .0 32 To ta l P A , C PM vm 94 4 ( 25 4) 92 7 ( 26 0) .3 55 97 7 ( 26 4) 99 0 ( 26 8) .23 6 91 8 ( 24 3) 87 0 ( 23 8) .0 38 Se den ta ry ti me , m in /d 58 1 (6 9) 58 3 ( 78 ) .7 19 58 0 ( 70 ) 57 5 ( 78 ) .4 89 583 (68 ) 59 1 ( 76 ) .2 15 Li gh t P A , m in /d 16 6 ( 29 ) 16 9 ( 33 ) .1 98 16 6 ( 31 ) 172 ( 36 ) .0 76 16 6 ( 29 ) 16 6 ( 29 ) .9 48 M od er ate P A , m in/ d 35 (9) 35 (11 ) .69 7 37 (1 0) 38 (1 2) .24 0 33 (8) 32 (9) .2 15 V ig or ous P A , min /d 25 (1 2) 23 (11 ) .07 2 27 (1 3) 26 (1 2) .5 46 23 (11 ) 20 (1 0) .0 17 M V PA , min /d 59 (1 9) 58 (2 9) .3 71 64 (2 1) 65 (2 1) .808 55 (17 ) 52 (17 ) .0 33 14 -1 5 y W hole w ee k n = 48 0 n = 25 5 n = 19 4 n = 10 7 n = 28 6 n = 14 8 To ta l P A , C PM v 38 4 (1 35 ) 38 7 ( 14 5) .75 7 41 8 ( 161 ) 43 7 ( 14 9) .3 08 36 0 ( 11 0) 351 (1 30 ) .41 2 To ta l P A , C PM vm 67 9 ( 20 0) 70 2 ( 214 ) .14 3 732 (23 5) 79 0 ( 231 ) .0 42 64 3 (1 63 ) 63 9 (17 6) .818 Se den ta ry ti me , m in /d 63 9 (7 1) 62 0 ( 82 ) .0 01 62 4 ( 74 ) 59 8 ( 80 ) .0 06 65 0 (6 6) 63 6 ( 81 ) .0 59 Li gh t P A , m in /d 12 5 (2 7) 13 0 (3 2) .01 5 129 (29 ) 14 0 ( 37 ) .0 05 12 2 (2 6) 12 3 (2 5) .6 06 M od er ate P A , m in/ d 27 (9) 28 (11 ) .14 6 28 (11 ) 31 (1 3) .0 30 26 (8) 26 (9) .7 29 V ig or ous P A , min /d 22 (1 2) 21 (1 2) .11 6 25 (1 5) 24 (11 ) .51 0 20 (1 0) 19 (1 2) .0 83 M V PA , min /d 49 (1 9) 49 (2 0) .7 99 53 ( 22 ) 55 (2 1) .4 55 47 (1 5) 44 (1 8) .1 76 (Co nti nue s)
low proportion of both boys and girls attained recommended levels of PA. Boys were more physically active than girls in all age groups. Furthermore, girls with high SES were more physically active than girls with low SES and this difference was not observed in boys.
These results were in line with other studies using objective methods of measuring PA, showing that the proportions of children and adolescents who met PA recommendations were low.12-14 The Swedish physical activity report card for 2018 also reported that overall PA, defined as the proportion of children and adolescents who adhered to the PA recommendation, was low.5 However, the data on which the Swedish report card was based did not have na-tionwide coverage. Studies reporting the proportions of popula-tions who are sufficiently physically active are contradictory, since different accelerometer protocols and cut-points to define MVPA have been used. The impact of using different cut-offs has been illustrated in previous reviews showing large discrepancies in the proportions of European children and adolescents who adhered to PA recommendations, ranging between 3% and 100%15 and 0% and 60%.12 The authors of these reviews concluded that the variation in results may reflect true variation as well as differences in meth-ods used to assess PA. Furthermore, Van Hecke et al12 reported that the average activity level varied between 492 and 804 counts per minute for children and between 486 and 647 counts per minute for adolescents. These mean values were higher than in the pres-ent study, where the mean activity levels were 500, 387 and 356 counts per minute for adolescents in the age groups 11-12, 14-15 and 17-18 years, respectively. This might be attributed to true differ-ences in national PA levels or different accelerometer protocols but might also be due to a decrease in PA over time showing that ado-lescents now are less physically active than at the time when these published studies were conducted.
The differences in PA between boys and girls have previ-ously been reported in a study with accelerometer data from
F I G U R E 4 Minutes in moderate and vigorous activity
(MVPA) during school time and leisure time by gender and age groups, (school-time: 11-12 years: boys n=571, girls n=599; 14-15 years: boys n=531, girls n=593; 17-18 years: boys n=437, girls n=571, leisure-time: 11-12 years: boys n=564, girls n=598; 14-15 years: boys n=513, girls n=589; 17-18 years: boys n=415, girls n=564) presented as means with 95% confidence intervals
0 5 10 15 20 25 30 35 40 45 11-12 y 14-15 y 17-18 y 11-12 y 14-15 y 17-18 y Leisure-time School-time Mniutes in MVPA Boys Girls To ta l M ea n ( SD ) B oy s M ea n ( SD ) G irl s M ea n ( SD ) H ig h S ES Lo w S ES P H ig h S ES Lo w S ES P H ig h S ES Lo w S ES P 17 -1 8 y W hole w ee k n = 37 4 n = 25 3 n = 13 1 n = 92 n = 24 3 n = 16 1 To ta l P A , C PM v 36 7 ( 14 6) 32 6 ( 11 6) <. 00 1 38 2 (1 65 ) 34 5 ( 127 ) .0 76 35 9 (1 34 ) 314 (1 09 ) .0 01 To ta l P A , C PM vm 60 5 ( 19 6) 56 5 (1 67 ) .0 08 62 1 ( 22 6) 58 2 ( 181 ) .17 2 59 7 (17 7) 55 6 (1 57 ) .0 17 Se den ta ry ti me , m in /d 65 5 ( 78 ) 665 (8 0) .11 8 64 9 (8 8) 66 8 ( 76 ) .0 87 65 8 ( 71 ) 66 3 (8 3) .53 3 Li gh t P A , m in /d 10 4 ( 27 ) 10 6 ( 27 ) .2 81 10 4 ( 30 ) 10 8 ( 26 ) .3 52 10 4 ( 26 ) 10 5 ( 28 ) .53 4 M od er ate P A , m in/ d 25 (1 0) 24 (1 0) .14 4 25 (1 2) 24 (11 ) .3 90 25 (1 0) 24 (1 0) .23 5 V ig or ous P A , min /d 24 (1 6) 20 (1 3) <. 00 1 26 (1 6) 22 (1 3) .0 64 24 (1 5) 18 (1 2) <. 00 1 M V PA , min /d 50 (2 1) 44 (1 8) <. 00 1 51 (2 3) 46 (1 9) .0 84 49 (1 9) 42 (1 8) .0 01 A bb re vi at io ns : C PM v, c ou nt s p er m in ut e ( ver tic al ); C PM vm , c ou nt s p er m in ut e ( ve ct or m ag ni tu de ); M V PA , m oder at e-to -v ig or ou s p hy si ca l ac tiv ity ; P A , p hy si ca l ac tiv ity ; SD , s ta nd ar d de vi at io n. T A B LE 3 (Co nti nue d)
27 637 children and adolescents from the International Children's Accelerometry Database (ICAD) showing that girls were more sed-entary and less active than boys at all ages.16
In the present study, the average sedentary time was 619 min-utes, which is higher than the study conducted by Ekelund et al,17 who reported an average of 354 minutes of sedentary time in 20 871 children and adolescents. The mean age of the participants in that study was 11.3 years compared to 14.4 years in the present study, which may partly explain the difference in results. Another explanation could be the use of different epochs where Ekelund used 60-second epochs whereas our study used 5-second epochs. Studies have shown that sedentary time decreased when longer epoch durations were employed.18,19 In the present study, the av-erage sedentary time was 10.3 hours, which was higher than results from a study conducted by Le Blanc et al,20 who reported that chil-dren (n = 5844) from around the world averaged 8.6 hours of sed-entary time. However, the mean age in that study was 10.4 years and thus lower than the mean age in the present study and once again, the age difference may partly explain the differences in the re-sults. For comparison, the participants in our study in the age group 11-12 years had a mean sedentary time of 9.7 hours. The usage of different epochs in studies also makes it difficult to compare PA lev-els and sedentary time between studies.
Moreover, our results showed that total PA, MVPA and seden-tary time were higher during weekdays than on weekends. Similar patterns have been reported in several other studies.21-23
The present study showed a difference in total PA and MVPA between girls with low and high SES, but there was no correspond-ing difference in sedentary time for either girls or boys. Similarly, a systematic review showed that higher SES was associated with higher levels of PA in adolescents in studies that used both subjec-tive and objecsubjec-tive measurements of PA.24 Our results on sedentary time contrasted with those from a study based on pooled data from 12,770 children and adolescents aged 10-18 years, which used ob-jective measurements of PA.25 In this study, adolescents whose mothers had university-level education had more sedentary time than adolescents whose mothers had high school-level education. Furthermore, those who had mothers with higher education spent less time in MVPA. Likewise, another study from the European Youth Heart Study showed positive associations between SES and children's sedentary time.26 However, these associations were not found in the samples from Norway and Denmark. Results from ear-lier studies are equivocal, which might be due to varying indicators of SES and measures of PA having been used, or to variations be-tween different countries.
The results showing low PA levels and high levels of sedentary time are of concern for the current and future health of Swedish adolescents, in particular, among girls with low SES. Importantly, the results can be used as important background information for researchers, stakeholders and policy makers in order to be able to identify problem areas and target groups and thereby be able to in-tervene appropriately.
4.1 | Strengths and limitations
This study was the first to analyse PA levels and sedentary time in a representative national sample of Swedish adolescents. A major strength of the present study was the nationwide, large sample size across the whole school year and inclusion of different age groups allowing for in-depth analyses. Another strength is the use of an ob-jective method, accelerometry, to measure PA and sedentary time. A limitation is, however, the cross-sectional design of the study. Another limitation is that only 22% of the selected schools partici-pated and that the school principal decided which classes that should be part of the survey. However, analyses of the non-response have shown that both the schools and the participants were representa-tive for the population with regard to socioeconomic background and school organisation.8 On the other hand, a further 27% were lost for the physical activity analyses. These participants were more likely to be boys, from the older age groups and from low SES. It is possible that the participating girls and boys were more motivated and that physical activity levels were somewhat overestimated. In addition, the time filter used for school time (8.00-15.59) would have been more precise if school schedules had been collected for each school class. The school days might have been shorter in the younger age groups and this could have led to that some of the leisure time have been included in the school time and that the time in MVPA is somewhat underestimated and sedentary time overestimated.
5 | CONCLUSION
This study showed that a low proportion of Swedish boys and, in particular, girls adhered to PA recommendations. Boys were more active than girls at all ages. Girls from families with low SES were less physically active than girls from families with high SES. Effective strategies to increase PA among adolescents, especially among girls with low SES, are urgently needed. The study provides Swedish's reference values for different age groups of adolescent boys and girls and can also be used as a baseline for future studies.
The results from this study may be an important knowledge base in order to promote physical activity and reduce sedentariness in young people and provide knowledge on which groups to focus on.
ACKNOWLEDGEMENTS
We wish to thank all the staff at the schools and all the students who have participated in this study. We would also like to thank the research team members who assisted with the data collection.
CONFLIC TS OF INTEREST
The authors declare no conflicts of interest.
FUNDING INFORMATION
This study was funded by The Swedish Research Council for Sport Science.
ORCID
Gisela Nyberg https://orcid.org/0000-0003-0004-8533
Andreas Fröberg https://orcid.org/0000-0002-3352-6661
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How to cite this article: Nyberg G, Kjellenberg K, Fröberg A,
Lindroos AK. A national survey showed low levels of physical activity in a representative sample of Swedish adolescents.
Acta Paediatr. 2020;00:1–12. https://doi.org/10.1111/
