Physical Activity and Sedentary Behaviors among Finnish Youth

Physical Activity and Sedentary Behaviors among Finnish Youth TUIJA TAMMELIN1, ULF EKELUND2, JOUKO REMES1, and SIMO NÄYHÄ1,3 Finnish Institute of Occupational Health, Oulu, FINLAND; 2Medical Research Council, Epidemiology Unit, Cambridge, UNITED KINGDOM; and 3Department of Public Health and General Practice, University of Oulu, FINLAND 1 ABSTRACT T he positive health effects of physical activity in young people include beneficial effects on cardiovascular, metabolic, and musculoskeletal health and on academic performance (3,18,24). Furthermore, physical activity seems to extend from youth to adulthood (14), and the health benefits of regular physical activity among adults are well documented (28). The current physical activity recommendations for young people state that all young people should be involved in physical activity of at least moderate intensity for at least 1 hIdj1 (4,24). Many young people fail to meet these recommendations; the proportion of sufficiently active young people is estimated at one third (20), with wide variations between age groups, genders, and countries. However, studies using direct measurements of activity have suggested higher estimates for the proportion of adequately active youths (82% for boys and 62% for girls) (19). The recent increase of obesity among young people (11,13) has been attributed to too much time spent in front of TV and computer screens (10). Similarly, an observed decrease in cardiorespiratory fitness among young people has been suggested to be at least partly attributable to increased sedentary behavior (26). According to the recent recommendation of the American Academy of Pediatrics (1), TV viewing in young people should be restricted to 2 hIdj1 to avoid negative effects on body weight and other health outcomes. According to displacement hypotheses, spending time watching TV, using computers, and playing video games reduces the time devoted to physically active pursuits. However, evidence supporting this hypothesis seems weak and contradictory. Some studies report a negative association between physical activity and TV viewing (15,25), whereas others have observed no association (7,9,29). Computer use shows a negative association with physical activity in some studies (15) but a positive association in others (9,22,29). Current information is needed about the prevalence of physical activity and sedentary behaviors and their associations, to develop effective strategies aimed to enhance a physically active lifestyle among young people. Examining associations between physical activity and sedentary behaviors can provide important information about the possibilities of enhancing physical activity by decreasing the amount of time spent on certain sedentary behaviors. The purpose of this study was to determine the prevalence of young Finns currently meeting international guidelines for physical activity and TV viewing, and to examine the associations between the levels of physical Address for correspondence: Tuija Tammelin, Ph.D., Finnish Institute of Occupational Health, Oulu, Aapistie 1, FIN-90220 Oulu, Finland; E-mail: [email protected]. Submitted for publication December 2006. Accepted for publication March 2007. 0195-9131/07/3907-1067/0 MEDICINE & SCIENCE IN SPORTS & EXERCISEÒ Copyright Ó 2007 by the American College of Sports Medicine DOI: 10.1249/mss.0b13e318058a603 1067 Copyright @ 2007 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. BASIC SCIENCES TAMMELIN, T., U. EKELUND, J. REMES, and S. NÄYHÄ. Physical Activity and Sedentary Behaviors among Finnish Youth. Med. Sci. Sports Exerc., Vol. 39, No. 7, pp. 1067–1074, 2007. Purpose: There is general concern about the low level of physical activity and the high amount of time devoted to sedentary behavior among adolescents. This study aimed to determine the proportion of young Finns meeting the current guidelines for youth physical activity (Q 60 min of moderate- to vigorous-intensity physical activity per day) and TV viewing (G 2 hIdj1) and to examine associations between physical activity and different sedentary behaviors. Methods: The study population consisted of 6928 boys and girls, members of the northern Finland birth cohort 1986 who, in 2001–2002, at age 15–16 yr, responded to a mailed questionnaire inquiring about their time spent in moderate to vigorous (MVPA), light (LPA), and commuting (CPA) physical activity, and different sedentary behaviors. Results: Fifty-nine percent of the boys and 50% of the girls reported 60 min or more of total physical activity per day. Only 23% of boys and 10% of girls reported 60 min of MVPA per day. Fortyeight percent of boys and 44% of girls reported more than 2 h of daily TV viewing. High amounts of TV viewing and computer use were associated with lower levels of physical activity in both genders. Conclusion: Many adolescents exceeded the recommended level of TV viewing and did not meet current recommendations for health-related physical activity. The inverse associations of physical activity with TV viewing and computer use suggest that measures aimed to reduce sedentary behaviors may, at least partly, increase physical activity among youth. Key Words: YOUNG PEOPLE, ADOLESCENTS, EXERCISE, SPORT, INACTIVITY, SITTING BASIC SCIENCES FIGURE 1—Levels of physical activity. Reclassification based on moderate to vigorous, light, and commuting physical activity outside school hours. activity and different sedentary behaviors. We also wanted to evaluate the test–retest reliability of the physical activity questionnaire used. METHODS This study is part of the Northern Finland Birth Cohort Study 1986 (NFBC 1986). This cohort comprises 9479 children from the two northernmost provinces of Finland—Oulu and Lapland—whose expected date of birth was between July 1, 1985 and June 30, 1986. The follow-up survey was carried out in 2001–2002, when the cohort members were 15–16 yr old. Each participant who was still alive and whose address was known (N = 9215) was mailed a questionnaire. The questionnaires were mailed to all cohort members at the same time, in April 2001. Of them, 7344 (80%) responded. The present analyses include those 6928 subjects (3336 boys and 3592 girls) who returned the questionnaire and gave their written permission to use data in scientific research. The number of individuals varies slightly in different analyses because some individuals did not answer all items of physical activity and sedentary behaviors. The test–retest reliability of the physical activity questions was evaluated in a separate group of 86 school children aged 15–16 yr who completed the questionnaire twice, 2 wk apart. A written informed consent was obtained from all individuals and their parents. The research was approved by the ethics committee of Oulu University Hospital. shortage of breath (here referred to as LPA). Additionally, the frequency of participation on moderate to vigorous physical activity was asked by a question, ‘‘How often do you participate in brisk physical activity outside school hours at least 20 min at a time? (at least some sweating and getting out of breath).’’ Commuting physical activity. The subjects were asked about their daily time spent in physically active commutes to and from school. The response alternatives—not at all, less than 20 min, 20–39 min, 40–59 min, and at least 1 hIdj1—were multiplied by five (five school days a week) to correspond to 0, 1, 2.5, 3.75, and 5 hIwkj1. Level of leisure-time physical activity. The overall level of physical activity outside school hours was estimated using information on MVPA, LPA, and commuting physical activity (CPA), as indicated in Figure 1. The new categories—very active, active, moderately active, somewhat active, and inactive—are based on the duration and intensity of physical activity outside school hours. For example, physically inactive individuals are defined as those participating less than 1 hIwkj1 in MVPA and less than 2 hIwkj1 in LPA and CPA. TABLE 1. Physical activity outside school hours in boys and girls at 16 yr of age. Boys N = 3336 (%) Frequency of participation in moderate to vigorous physical activity for at least 20 min at a time Never 4.5 Once a month or less often 9.1 2–3 times a month 8.8 Once a week 10.8 Twice a week 12.4 3 times a week 17.4 4–6 times a week 20.4 Daily 16.7 Moderate to vigorousb physical activity (hIwkj1) Not at all 6.8 about 0.5 12.6 about 1 12.0 2–3 23.4 about 4–6 22.2 7 23.0 b j1 Light physical activity (hIwk ) Not at all 6.7 about 0.5 12.7 about 1 20.8 2–3 31.8 about 4–6 15.4 7 12.6 Commuting physical activity to school (minIdj1) Not at all 14.6 G 20 42.6 20–39 28.3 40–59 6.2 at least 60 8.3 The level of leisure-time physical activityc Inactive 10.7 Somewhat active 20.4 Moderately active 23.4 Active 22.3 Very active 23.1 Measurement of Physical Activity and Sedentary Behavior Light, moderate, and vigorous physical activity. The amount of physical activity outside school hours was evaluated separately for moderate to vigorous physical activity (MVPA) and light physical activity (LPA) by asking, ‘‘How many hours a week altogether do you participate in a) brisk and b) light physical activity outside school hours?’’ In the questionnaire, the term brisk was defined as physical activity causing at least some sweating and getting out of breath (here referred to as MVPA), and the term light as physical activity causing no sweating or 1068 Official Journal of the American College of Sports Medicine Girls N = 3592 (%) b P a 0.001 2.8 11.3 12.5 14.5 16.7 17.5 16.4 8.2 0.001 6.9 14.8 18.9 29.9 19.8 9.7 0.001 4.5 11.6 20.9 35.3 17.2 10.5 0.001 13.5 42.0 33.0 6.3 5.2 0.001 8.6 31.9 29.9 19.9 9.7 a From a Pearson chi-square test for gender difference in distributions. Moderate to vigorous physical activity was defined as causing at least some sweating and getting out of breath; light physical activity was defined as causing no sweating or shortness of breath. c Categorization shown in Figure 1. b http://www.acsm-msse.org Copyright @ 2007 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. TABLE 2. Time spent in sedentary activities outside school hours in boys and girls at 16 yr of age. Boys N = 3336 (%) Girls N = 3592 (%) j1 a a 0.003 13.1 42.8 22.8 21.3 0.001 60.3 36.7 3.0 0.001 22.3 68.7 9.0 0.001 20.4 54.7 24.9 0.001 7.7 26.6 38.6 27.2 From a Pearson chi-square test for gender difference in distributions. Sedentary behaviors. In response to an open-ended question, participants reported how many hours per day, on average, they spent on the following sedentary activities outside school hours: TV viewing, reading books or magazines, playing or working on a computer/playing video games, and on other sedentary activities. The total time spent on all of these sedentary activities was also calculated. Statistical Methods The gender differences in the distributions of variables were tested by Pearson`s chi-square test. The analysis of the RESULTS Physical activity. Boys were more physically active than girls, especially regarding MVPA; 23% of boys and 10% of girls reported participation in MVPA for at least 7 hIwkj1 (Table 1). Approximately 20% of the adolescents reported participating in MVPA for less than 1 hIwkj1, with TABLE 3. Selected physical activity recommendations, operational definitions for the present study, and proportion of boys and girls meeting the recommendations in the sample studied. Source Strong et al. (24) American Academy of Paediatrics (1) Pate et al. (17) American College of Sports Medicine (2) Goal, Target Group, and Content of Physical Activity Recommendation Health for school-aged youth (6–18 yr): daily participation in Q 60 min of moderate to vigorous physical activity To avoid negative effects of TV viewing in children and adolescents: e 1–2 hIdj1 spent with entertainment media Health for adults: accumulation of at least 30 min of at least moderate intensity on preferably all days of the week To develop and maintain cardiorespiratory fitness in adults: exercise three to five times per week, 20–60 min at a time, at the intensity level of 60–90% of maximum heart rate Operational Definition for the Present Study a) MVPA, LPA, and CPA for Q 7 hIwkj1 b) Only MVPA for Q 7 hIwkj1 Viewing TV for e 2 hIdj1 a) MVPA, LPA, and CPA for Q 3.5 hIwkj1 b) Only MVPA for Q 3.5 hIwkj1 MVPA three times a week or more, often Q 20 min at a time Boys and Girls Meeting the Recommendations Boys (%) Girls (%) a) 59 a) 51 b) 23 b) 10 52 56 a) 83 a) 84 b) 45 b) 30 54 42 MVPA (moderate to vigorous physical activity) was defined as causing at least some sweating and getting out of breath. LPA (light physical activity) was defined as causing no sweating or shortness of breath. CPA (commuting physical activity) included physically active commuting to school and back. PHYSICAL ACTIVITY AND SEDENTARY BEHAVIORS Medicine & Science in Sports & Exercised 1069 Copyright @ 2007 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. BASIC SCIENCES Viewing TV (hId ) G1 12.5 1–2 39.5 2.5–3.9 23.0 Q4 24.9 Using computer or playing video games (hIdj1) G1 19.3 1–2 56.7 92 24.0 Reading books or magazines (hIdj1) G1 33.6 1–2 61.4 92 5.0 Other sedentary activities (hIdj1) G1 28.4 1–2 54.6 92 17.0 Total time spent on sedentary activities (hIdj1) G3 7.0 3–4.9 18.9 5–7.9 39.0 Q8 35.1 P associations between physical activity and sedentary behaviors was based on one-way cross-tabulations in which the variables were arranged to form ordinal classes. The correlations between the variables were assessed by the Goodman–Kruskal gamma statistics test, which expresses the surplus of concordant over discordant pairs of observations. The values of gamma range between j1 and +1; a positive value indicates a direct association, and a negative value indicates an inverse association. The differences in the prevalence of inactivity between categories of sedentary behaviors were expressed as prevalence ratios and their 95% confidence intervals. The test–retest reliability of the physical activity questions was evaluated by calculating the intraclass correlation coefficients that represent test–retest variability on the basis of one-way analysis of variance. The following ratings on agreement level were classified as 0– 0.2 = poor, 0.2–0.4 = fair, 0.4–0.6 = moderate, 0.6–0.8 = substantial, and 0.8–1.0 = almost perfect (12). Percent agreement (%A) was calculated as the number of subjects who were classified in exactly same category on both occasions as a proportion of the total number of subjects. Percent agreement T 1 (%A T 1) describes the proportion of students who were classified in exactly the same category or next to the same category (T 1 category). SPSS software (version 14.0.1) was used for statistical analyses (23). Subjects meeting physical activity recommendations. Table 3 displays the operational definitions of the current physical activity recommendations used in the present study, and the proportion of boys and girls who met these recommendations. According to the recommendation proposed for young people (24), 59% of the boys and 51% of the girls were sufficiently active when all forms of physical activity (MVPA, LPA, CPA) were considered. However, only 23% of boys and 10% of girls met this recommendation when only self-reported MVPA was considered. Approximately 50% of boys and girls viewed TV for 2 hIdj1 or less, thus meeting the healthbased criteria for children and adolescents (1). Approximately one third (32% of boys and 30% of girls) met both no marked differences between the genders, whereas 11% of boys and 9% of girls were classified as inactive, reporting almost no physical activity (Table 1). Sedentary behaviors. Almost 50% of the participants reported that they watched TV for more than 2 hIdj1, and 25% of the boys and 21% of the girls reported watching TV for at least 4 hIdj1 (Table 2). In addition, 24% of the boys, but only 3% of the girls, used the computer or played video games for more than 2 hIdj1. In contrast, a slightly larger proportion of girls reported that they read books or magazines (9 vs 5%) or spent that amount of time on other sedentary activities (25 vs 17%). Overall, a larger proportion of boys than girls reported that they spent 8 h or more on sedentary activities of some kind (Table 2). BASIC SCIENCES TABLE 4. The level of physical activity according to time spent in different sedentary activities in boys and girls aged 15–16 yr. Daily Time Spent on Different Sedentary Activities Level of Physical Activity N Inactive % Ordinal Correlation Somewhat Active % Moderately Active % Active % Very Active % Total % 16 21 20 23 30 22 24 22 24 22 22 23 21 25 24 20 100 100 100 100 32 30 33 34 35 29 30 29 21 23 19 15 7 11 10 8 100 100 100 100 22 19 23 19 24 25 22 24 19 26 24 19 100 100 100 32 32 34 31 29 22 20 20 20 10 9 8 100 100 100 20 20 21 20 25 21 22 22 24 25 22 24 100 100 100 34 31 31 26 32 29 19 20 19 11 9 9 100 100 100 17 22 23 22 24 24 24 22 21 26 23 20 100 100 100 30 31 36 26 31 30 22 21 16 13 10 7 100 100 100 15 17 20 23 25 23 23 23 23 24 23 21 24 27 25 19 100 100 100 100 29 30 31 35 30 30 30 30 25 22 20 17 13 13 10 7 100 100 100 100 Gammaa P j0.041 0.003 j0.064 0.001 j0.062 0.001 j0.043 0.001 0.004 0.800 0.012 0.437 j0.052 0.001 j0.082 0.001 j0.076 0.001 j0.104 0.001 j1 Viewing TV (hId ) Boys G1 401 8 1–2 1283 11 2.5–3.9 755 10 Q4 811 13 Girls G1 460 5 1–2 1508 8 2.5–3.9 798 8 Q4 755 14 Using the computer or playing video games (hIdj1) Boys G1 620 11 1–2 1843 9 >2 784 15 Girls G1 2117 7 1–2 1282 10 >2 105 16 Reading books or magazines (hIdj1) Boys G1 1087 13 1–2 1993 10 >2 162 10 Girls G1 785 11 1–2 2420 8 >2 318 11 Other sedentary activities (hIdj1) Boys G1 886 11 1–2 1725 10 >2 532 12 Girls G1 690 8 1–2 1867 7 >2 849 11 Total time spent on sedentary activities (hIdj1) Boys G3 209 12 3–4.9 593 9 5–7.9 1220 8 > 7.9 1096 13 Girls G3 260 4 3–4.9 899 6 5–7.9 1305 9 > 7.9 922 12 a Goodman gamma indicates the surplus of concordant pairs over discordant pairs. 1070 Official Journal of the American College of Sports Medicine http://www.acsm-msse.org Copyright @ 2007 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. FIGURE 3—Prevalence ratios and their 95% confidence intervals for being physically inactive at the age of 16 yr, according to time spent using the computer or playing video games. Test–retest reliability coefficients for different questions on physical activity and sedentary behaviors ranged between 0.48 and 0.83, being highest for MVPA and for questions about reading books and magazines, and lower for other types of activities and sedentary behaviors (Table 5). DISCUSSION Our results suggest that approximately 50% of Finnish boys and girls do not meet the current recommended levels of physical activity. A similar percentage of adolescents exceed the recommended levels of TV viewing for young people. Physical activity was inversely associated with the time spent viewing TV, using the computer, and playing video games in both genders. Physical activity and sedentary behavior in relation to recommendations and earlier studies. The proportion of boys and girls classified as sufficiently active differed depending on the recommendation chosen and on whether MVPA or a combination of MVPA, LPA, TABLE 5. Test–retest reliability of physical activity questionnaire fulfilled twice by 86 school children ages 15–16 yr, 2 wk apart. Variablesa Moderate to vigorous physical activity Light physical activity Commuting physical activity to school The level of leisure-time physical activity TV viewing Using the computer or playing video games Reading books and magazines Other sedentary activities Total time spent on sedentary activities ICC (95% CI) %A %A T 1 0.83 (0.74–0.88) 57 92 0.49 (0.31–0.63) 0.57 (0.41–0.70) 30 66 83 97 0.78 (0.68–0.85) 59 92 0.74 (0.63–0.82) 0.48 (0.29–0.63) 69 67 100 100 0.81 (0.73–0.87) 85 100 0.52 (0.34–0.67) 0.78 (0.68–0.85) 69 59 99 94 a FIGURE 2—Prevalence ratios and their 95% confidence intervals for being physically inactive at the age of 16 yr, according to time spent viewing TV. PHYSICAL ACTIVITY AND SEDENTARY BEHAVIORS Categories of the variables are presented in Tables 1 and 2. ICC (95% CI), intraclass correlation coefficients and 95% confidence interval; %A, the proportion of subjects who were classified in exactly the same category in both settings; %A T 1, the proportion of subjects who were classified in exactly the same category or next to the same category (T 1 category) in two different tests. Medicine & Science in Sports & Exercised 1071 Copyright @ 2007 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. BASIC SCIENCES the recommendation for physical activity (24) (all physical activity considered) and the recommendation for TV viewing (1), whereas one fifth (21% of boys and 23% of girls) did not fulfill either of these recommendations. If the recommendations for adults by Pate et al. (17) were used as criteria, 85% of the boys and 84% of the girls would be categorized as being sufficiently active when including all physical activity, but only 45% of the boys and 30% of the girls were sufficiently active when just MVPA was considered. Finally, 54% of the boys and 42% of the girls met the ACSM adult recommendations aimed to maintain and increase cardiorespiratory fitness (2). Association of physical activity and sedentary behaviors. All types of sedentary activities except reading books or magazines were inversely correlated with the level of physical activity (P G 0.001) (Table 4). The gamma coefficient for total time spent on sedentary activities in boys and girls, for example, were j0.104 and j0.076, respectively, indicating a 10 and 8% lower occurrence, respectively, of concordant as opposed to discordant observations (i.e., a decrease in physical activity along with increasing sedentary behaviors). The proportion of inactive individuals was highest among those who watched TV at least 4 hIdj1 and was lowest among those who watched TV less than 1 hIdj1 (14 vs 5% in girls, and 13 vs 8% in boys). A similar trend in inactivity was seen in computer use; the proportion on inactive boys (15%) and girls (16%) was highest among those who used the computer more than 2 hIdj1 (Table 4). The prevalence of physical inactivity was, respectively, 1.6- and 2.5-fold in boys and girls who viewed TV at least 4 hIdj1 compared with those who did so less than 1 hIdj1 (Fig. 2). The respective prevalence ratios were 1.4 and 2.2 for boys and girls who used the computer or played video games for more than 2 hIdj1, compared with those who did so less than 1 hIdj1 (Fig. 3). The proportions of active and very active adolescents were lowest among those who reported spending the most time viewing TV and using the computer. BASIC SCIENCES and CPA was considered. Our observation that one half of Finnish boys and girls met the level of physical activity recommended for young people (24) may be an optimistic estimate, because the time spent on LTPA and CPA was included. A higher proportion of adolescents was categorized as sufficiently active according to the recommendations established for adults (17). This recommendation is also suggested for currently inactive adolescents (24). Although criticism has been directed against the scientific evidence for physical activity recommendations for young people (27), there is a consensus that young children need more physical activity than adolescents, who, in turn, need more physical activity than adults for optimal health (4,24). Any comparison between our results and those obtained in other studies is difficult because different methods, recommendations, and definitions have been used. Our questions used to estimate MVPA are almost identical to those used in the international survey of school-aged children who were 11–15 yr in 2001–2002 (5). Our findings are in close agreement with their results of the Finnish population sampled, in that 45% of boys and 33% of girls participated in MVPA for 4 h or more per week at age 15 yr (30). Using a slightly different definition (moderate-intensity exercise on 5 dIwkj1 for a total of at least 60 minIdj1), Roberts et al. (20) estimate that 27% and 20% of Finnish 15-yr-old boys and girls were sufficiently active. Watching TV and using computers constitutes a significant part of young people`s leisure time, especially among boys. The amount of time spent watching TV in our study is very similar to the amounts reported elsewhere for adolescents aged 11–15 yr: 26% of adolescents viewed TV for at least 4 hIdj1 on weekdays, and the proportion was 45% during weekends (25). Similarly, our results that suggest high levels of computer use among boys, and a great gender difference, corroborate previous findings (25). In our study, girls reported a greater amount of time spent on other sedentary activities. These activities may include homework, which has previously occupied more of girls` leisure time compared with boys (25). Associations between physical activity and sedentary behaviors. Previous observations regarding a possible association between physical activity and sedentary behaviors have been contradictory. Some studies have combined all types of sedentary behaviors and have observed no association with the level of physical activity (6). It also has been suggested that the associations may vary with respect to different sedentary behaviors and gender, and between weekdays and weekends (25). The inverse association between TV viewing and physical activity observed in our study is in agreement with a previous meta-analysis by Marshall et al. (15), which suggests a significant but weak inverse association. Similarly, Santos et al. (22) observed an inverse association between physical activity and sedentary behavior, although only during weekends. Finally, in the WHO international study (25), a significant inverse association was found 1072 Official Journal of the American College of Sports Medicine between TV time and physical activity in most countries and regions in girls, but not in boys. The inverse association between computer use and physical activity in boys in the present study is similar to that described previously (15,25). However, others have observed a positive association between computer time and physical activity (22,29), and this association may vary by gender and country (25). Discussion of methods. Reliance on self-reported measures of physical activity is a limitation in our study. Social desirability may lead to overreporting of physical activity (21), and the number of sufficiently active adolescents may, therefore, actually be lower than that reported. Physical activity at school was not assessed in the present study, and this may have led to underestimation of the number of sufficiently active adolescents. Similarly, it is likely that a questionnaire would be unable to capture all different types of physical activity. Studies using objective methods to assess physical activity levels in young people have suggested that the vast majority of young people actually meet the current recommendations for physical activity (8,16,19). However, objective measurements were not feasible in our representative sample of more than 9000 adolescents. Our results suggest a reasonable reliability of the questionnaire. The total time spent on all sedentary activities may be considered rough estimates because different sedentary behaviors may overlap. Some sedentary behaviors, such as reading magazines or doing homework, may be performed simultaneously while watching TV. CONCLUSIONS AND FUTURE DIRECTIONS Our results provide some support for the displacement hypothesis, suggesting that sedentary behaviors replace the time for physically active pursuits. It seems that there are possibilities to increase physical activity by reducing sedentary behavior among those who view TV for more than 4 hIdj1 or who use the computer for more than 2 hIdj1. Although TV viewing is a prevalent sedentary behavior, it may not be a marker of overall sedentary behavior. Ekelund et al. (7) have come to the same conclusion in their recent study suggesting no association between TV viewing and objectively measured physical activity. In our study, a large proportion of those who watched TV for 4 h or more were classified as physically active or very active (43% of boys and 23% of girls), suggesting that high levels of physical activity can be combined with high levels of TV viewing in many adolescents. Our results were obtained in a large population-based cohort, the response rate was high, and it is likely that these observations can be generalized to other countries with similar access to TV sets and computers. As in any observational study, we cannot assert causality. Only intervention studies targeted to decrease sedentary behaviors could provide more information about causal effects on physical activity. Further research is needed about the dose–response association http://www.acsm-msse.org Copyright @ 2007 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. between sedentary behaviors and health outcomes to more accurately define the safety level for different sedentary pursuits. Information about prevalence, trends in, and correlates of sedentary behaviors is also needed. These studies should include accurate, objective measurements of sedentary behaviors, such as accelerometers combined with diaries, during both weekdays and weekends and during different seasons. Many adolescents spend too much time watching TV and using computers and do not engage in sufficient amounts of physical activity according to current recommendations. Our results suggest that approximately 50% of Finnish adolescents are sufficiently active according to current recommendations, and an equal amount of young people watch TV for more than 2 hIdj1. Preventive initiatives to reduce sedentary behavior and to increase physical activity are likely to be successful if they are targeted toward the approximately 20% of adolescents who do not meet the current activity recommendations and who watch TV for more than 2 hIdj1. This study was partly funded by the Ministry of Education and the Research Foundation of the Institute of Sports, Finland (Urheiluopistosäätiö). REFERENCES PHYSICAL ACTIVITY AND SEDENTARY BEHAVIORS 14. MALINA, R. M. Physical activity and fitness: pathways from childhood to adulthood. Am. J. Human Biol. 13:162–172, 2001. 15. MARSHALL, S. J., S. J. BIDDLE, T. GORELY, N. CAMERON, and I. MURDEY. Relationships between media use, body fatness and physical activity in children and youth: a meta-analysis. Int. J. Obes. Relat. Metab. Disord. 28:1238–1246, 2004. 16. PATE, R. R., P. S. FREEDSON, J. F. SALLIS, et al. Compliance with physical activity guidelines: prevalence in a population of children and youth. Ann. 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