Palabras claves: DEPORTE ESCOLAR/ ACTIVIDAD FÍSICA
Título: COMPARISON OF SELF-REPORTED AND OBJECTIVELY MEASURED PHYSICAL ACTIVITY LEVELS OF ADOLESCENTS
Autor: Jarmo Liukkonen, Arto Gråstén
País: Finlandia
Abstract
According to the recommendations, all secondary school-aged students should be physically active for at least 60 minutes on a daily basis. A review of recent nationally representative studies based on self-reported physical activity (PA), however, showed that only 10−40% of Finnish adolescents achieve these recommended levels.The aim of the study was to examine if directly measured and self-reported PA differ by gender or grade, and to analyze the predictive strength of self-reports on direct PA in a cross-sectional sample of Finnish secondary school students(58 girls, 38 boys).Accelerometers (Polar Active) were used for the direct assessment of students’ PA during a one-week period.Self-reported PA was assessed using the Moderate to Vigorous Physical Activity (MVPA) measure. The MANOVA yielded a significant main effect for grade in directly measured PA and self-reported PA. Tukey’s HSD -test revealed that Grade 7 students were significantly more physically active than Grade 9 students when PA was measured using self-reports (p < .01).
The results of the linear regression analyses conducted for each grade level indicated that self-reported PA emerged as the significant positive predictor for students’ directly measured PA within Grade 8 and Grade 9 students. Self-reported PA was not a significant contributor for Grade 7 students’ direct PA.Results for selfreported PA indicated that only 11% of adolescents met the requirement for minimum 60 minutes of MVPA per day. In contrast, 85% met the recommendation based on direct measure scores. Overall, the results highlighted the continuing need of objective PA studies involving Finnish children and adolescents.
Introduction
According to the recommendations of health experts, all secondary school-aged
students should be physically active for at least 60 minutes on a daily basis (World
Health Organization 2012). A review of recent nationally representative studies
based on self-reported PA (Finnish Board of Education 2011; Ministry of Social
Affairs and Health 2007; National Institute for Health and Welfare 2010), however,
showed that only 10−40% of Finnish adolescents achieve these recommended
levels. Similarly, self-report data drawn from large sample studies in the US indicated
that the minority of adolescents (37−41%) had five or more sessions of moderate to
vigorous PA (MVPA) per week (Gordon-Larsen, Nelson&Popkin 2004). In addition,
when the activity was assessed directly using accelerometers, Troiano et al. (2008)
reported that within a large sample of U.S. adolescents, only 8% obtained the
recommended 60 minutes of PA on a daily basis. The gap between self-reports and
directly measured scores makes it difficult to estimate the real level of physically
active adolescents. The current study compared direct technique (accelerometer) to
more traditional subjective method (questionnaire) for the assessment of PA in a
cross-sectional sample of Finnish secondary school students.
During adolescence, opportunities for PA consist mainly of commuting to school,
school physical education (PE), PA during recess and leisure time, participation in
sports, and unorganized PA. Typical PA measurement techniques used with
adolescents do not detect several dimensions of PA, i.e. frequency, type, intensity,
and duration (Dale, Welk&Mattews 2002).
Direct measures can provide important insights into the true activity levels of
adolescents (Bates 2006) and the main techniques (e.g., accelerometers,
multichannel activity monitors, heart rate monitors) have been shown to provide
more accurate measures of PA than self-reported methods in children and
adolescents (Bates 2006; de Vries et al. 2006; Trost 2000).
Self-reported PA measures have been used widely in many countries including
Finland to assess overall PA, for economical and practical purposes. However,
previous findings have shown that children and adolescents are less able than adults
to recall their PA levels, indicating that questionnaires provide a restricted measure
of PA in children and adolescents (Marshall, and Welk, 2008). The correlation
between self-reported and directly measured PA has varied as a function of the
method used (Moore, Maloney & Yin 2007; Prochaska, Sallis& Long 2001;
Shiely&MacDonncha 2009; Trost et al. 2002).
The specific aim of this study was to examine if directly measured and self-reported
PA differ by gender and grade. A second aim was to analyze the predictive strength
of self-reports on direct PA. The final aim was to investigate the proportion of
adolescents accumulating at least 60 minutes of moderate to vigorous physical
activity (MVPA) on a daily basis.
Participants and methods
Participants, 58 girls and 38 boys were recruited from a secondary school located in
Northeast Finland in spring 2011. Accelerometers (Polar Active) were used for the
direct assessment of students’ PA during a one-week period. Self-reported PA was
assessed using the Moderate to Vigorous Physical Activity (MVPA) measure
(Prochaska, Sallis& Long 2001). The items required students to summarize their
time spent in physical activity each day in the following way: 1) “When you think
about your typical week, on how many days you are physically active for a total of at
least 60 minutes per day?” and 2) “Over the past 7 days, on how many days were
you physically active for a total of at least 60 minutes per day?” Both items used an
eight-point response scale (0 to 7 days in a week). The mean of the two items was
calculated.
Results
The MANOVA yielded a significant main effect for grade in directly measured PA
(Wilks’s Λ = .89, F(1, 96) = 4.32, p < .05; ηp2 = .04) and self-reported PA (Wilks’s Λ
= .89, F(1, 96) = 10.86, p < .001; ηp2 = .11). Tukey’s HSD -test revealed that Grade
7 students were significantly more physically active than Grade 9 students when PA
was measured using self-reports (p < .01). No further differences were found.
The results of the linear regression analyses conducted for each grade level
indicated that self-reported PA emerged as the significant positive predictor for
students’ directly measured PA within Grade 8 students (p < .001), and Grade 9
students (p < .01), accounting for 41.6% and 17.3% of variance. Self-reported PA
was not a significant contributor for Grade 7 students’ direct PA.
Results for self-reported PA indicated that only 11% of adolescents met the
requirement for minimum 60 minutes of MVPA per day. In contrast, 85% met the
recommendation based on direct measure scores. Self-report data indicated that a
minimally larger portion of Grade 8 students (13.1%) achieved the recommendation
than either Grade 7 (12.0%) or 9 students (9.3%). Conversely, a higher percentage
of Grade 7 students (92.0%) met the requirement of 60 minutes daily PA when
assessed by direct measures than either Grade 8 (76.3%) or 9 (85.2%) students.
Discussion
Currently, no studies that incorporate both direct and self-reported measures of PA
with samples of Finnish adolescents have been undertaken. The current study
revealed that girls and boys were similarly physically active, based on PA measured
using both accelerometers and questionnaires. Results also indicated that Grade 7
students were physically more active than Grade 9 students when PA was assessed
using self-reports but no significant difference was found when direct measure
scores were used. In addition, the associations between self-report and
accelerometer scores were stronger for Grade 8 and 9 students than those in Grade
7. Unexpectedly, a majority of the students achieved 60 minutes of MVPA per day
when PA was measured directly. In turn, self-reports revealed a smaller portion of
students who met the recommendation. Overall, the results highlighted the
continuing need of objective PA studies involving Finnish children and adolescents.
No significant gender differences were found for either self-reported or directly
measured PA. This unexpected finding was not in line with previous research that
showed boys were physically more active than girls based on both self-reports
(Duncan et al. 2004; Finnish Board of Education 2011; Yli-Piipari 2011; World Health
Organization 2004, 2008) and direct measure scores (Sherar et al. 2007; Trost et al.
2002).
This was the first attempt to examine the predictive relationship between selfreported
and directly measured PA within Finnish secondary school students. The
strength of the current study was that the direct data was collected for 24 hours per
day over a one-week period. Trost et al. (2000) recommended that at least a sevenday
monitoring protocol is needed in order to provide reliable estimates of the usual
PA behavior of children and adolescents. The possible reasons for the predictive
differences may be that the present self-report scale ignored factors such as
localized socio-cultural influences or socioeconomic status, which has been
previously shown to affect self-reports of PA (Bates 2006). For example, the social
support from friends (Bergh et al. 2011), within a certain PE group is difficult to
identify, and as a consequence have either positive or negative effects on self-report
scores. Adolescents may purposely under-report or over-report health and well-being
behaviors including PA, because they believe engaging in these behaviors is socially
undesirable or desirable (Brener, Billy & Grady 2003). Taken together, the results of
this study indicated that Grade 8 and 9 students managed to self-report their daily
PA with a higher level of association to their directly measured PA than the Grade 7
students. Based on the current and previous findings (Prochaska, Sallis& Long 2001;
Shephard 2003), researchers need to be cautious when determining actual PA by
self-report with adolescent samples because the scores may only provide basic
estimates of the actual behavior irrespective of the method used (Marshall&Welk
2008).
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