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      Does the frequency and intensity of physical activity in adolescence have an impact on bone? The Tromsø Study, Fit Futures

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          Abstract

          Background

          Optimization of the genetic potential for bone accrual in early life may prevent future fractures. Possible modification factors include lifestyle factors such as nutrition and physical activity. Measured levels of bone mineral density (BMD) and bone mass content (BMC) are indicators of bone strength, and are correlated with fracture risk. This study explored the impact of self-reported physical activity frequencies and intensity on BMD and BMC in Norwegian adolescents.

          Methods

          In 2010–2011 school students in two North-Norwegian municipalities were invited to a health survey, the Fit Future study. 508 girls and 530 boys aged 15–18 years attended. BMD and BMC were measured by dual X-ray absorptiometry. Physical activity and other lifestyle-factors were reported by questionnaires and clinical interviews. Statistical analyses were performed sex stratified, using ANOVA for comparison of means and linear regression models adjusting for factors known to affect bone.

          Results

          Approximately 2/3 of girls and boys reported themselves as physically active outside school hours. Active participants had a significantly higher BMD and BMC at all sites ( p < 0.001), except for BMC total body in girls, compared to inactive participants. In multiple linear regression analyses, increased physical activity measured as days a week, categorized into seldom, moderate and highly, was positively associated with BMD (g/cm 2) at all sites in girls. Girls reporting themselves as highly active had BMD levels 0.093 g/cm 2, 0.090 g/cm 2 and 0.046 g/cm 2 higher ( p < 0.001) than their more seldom active peers at femoral neck, total hip and total body respectively. Corresponding values for boys were 0.125 g/cm 2, 0.133 g/cm 2 and 0.66 g/cm 2. BMC measures showed similar trends at femoral neck and total hip.

          Conclusions

          Increased level of physical activity is associated with higher BMD and BMC levels in adolescents. For both sexes high activity frequency seems to be essential, whilst boys reporting quite hard intensity has an additional impact. The differential effects of physical activity on bone strength in adolescence have clinical implications, especially in preventive strategies.

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          Most cited references30

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          Limits to the measurement of habitual physical activity by questionnaires.

          Despite extensive use over 40 years, physical activity questionnaires still show limited reliability and validity. Measurements have value in indicating conditions where an increase in physical activity would be beneficial and in monitoring changes in population activity. However, attempts at detailed interpretation in terms of exercise dosage and the extent of resulting health benefits seem premature. Such usage may become possible through the development of standardised instruments that will record the low intensity activities typical of sedentary societies, and will ascribe consistent biological meaning to terms such as light, moderate, and heavy exercise.
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            Tracking of Physical Activity from Childhood to Adulthood: A Review

            The aim of the article was to review studies on the tracking of physical activity in all phases of life from childhood to late adulthood. The majority of the studies have been published since 2000. The follow-up time in most studies was short, the median being 9 years. In men, the stability of physical activity was significant but low or moderate during all life phases and also in longterm follow-ups. In women, the tracking was lower and in many cases non-significant. Among both sexes, stability seems to be lower in early childhood than in adolescence or in adulthood and lower in transitional phases, such as from childhood to adolescence or from adolescence to adulthood, than in adulthood. However, the differences in the stability of physical activity between age groups and between different phases of life were small. The number of tracking studies utilising objective methods to measure physical activity was so small that systematic differences in stability between self-report and objective methods could not be determined. A factor which caused differences in tracking results was the adjustment of correlations for measurement error and other error variance. Adjusted coefficients were clearly higher than unadjusted ones. However, adjustment was done only in very few studies. If the different methods used for estimating habitual physical activity and the failure to control for important covariates in studies of tracking are taken into account, physical activity appears to track reasonably well also in the longer term, for example from adolescence to adulthood. The results of the tracking studies support the idea that the enhancement of physical activity in children and adolescents is of great importance for the promotion of public health.
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              The reliability and validity of the physical activity questions in the WHO health behaviour in schoolchildren (HBSC) survey: a population study.

              To assess the test-retest reliability and validity of the physical activity questions in the World Health Organisation health behaviour in schoolchildren (WHO HBSC) survey. In the validity study, the Multistage Fitness Test was administered to a random sample of year 8 (mean age 13.1 years; n = 1072) and year 10 (mean age 15.1 years; n = 954) high school students from New South Wales (Australia) during February/March 1997. The students completed the self report instruments on the same day. An independent sample of year 8 (n = 121) and year 10 (n = 105) students was used in the reliability study. The questionnaire was administered to the same students on two occasions, two weeks apart, and test-retest reliability was assessed. Students were classified as either active or inadequately active on their combined responses to the questionnaire items. Kappa and percentage agreement were assessed for the questionnaire items and for a two category summary measure. All groups of students (boys and girls in year 8 and year 10) classified as active (regardless of the measure) had significantly higher aerobic fitness than students classified as inadequately active. As a result of highly skewed binomial distributions, values of kappa were much lower than percentage agreement for test-retest reliability of the summary measure. For year 8 boys and girls, percentage agreement was 67% and 70% respectively, and for year 10 boys and girls percentage agreement was 85% and 70% respectively. These brief self report questions on participation in vigorous intensity physical activity appear to have acceptable reliability and validity. These instruments need to be tested in other cultures to ensure that the findings are not specific to Australian students. Further refinement of the measures should be considered.
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                Author and article information

                Contributors
                +47 900 82 718 , tore.christoffersen@uit.no
                anne.winther@uit.no
                ole-andreas.nilsen@uit.no
                luai.ahmed@uit.no
                anne-sofie.furberg@uit.no
                guri.grimnes@uit.no
                emd@mrc.soton.ac.uk
                nina.emaus@uit.no
                Journal
                BMC Sports Sci Med Rehabil
                BMC Sports Sci Med Rehabil
                BMC Sports Science, Medicine and Rehabilitation
                BioMed Central (London )
                2052-1847
                10 November 2015
                10 November 2015
                2015
                : 7
                : 26
                Affiliations
                [ ]Department of Health and Care Sciences, UIT The Arctic University of Norway, Forskningsparken, Sykehusveien 21, NO-9037 Tromsø, Norway
                [ ]Finnmark Hospital Trust, Alta, Norway
                [ ]Division of Neurosciences, Orthopedics and Rehabilitation Services, University Hospital of North Norway, Tromsø, Norway
                [ ]Institute of Public Health, College of Medicine and Health Sciences, United Arab Emirates University, Al Ain, UAE
                [ ]Department of Community Medicine, UIT the Arctic University of Norway, Tromsø, Norway
                [ ]Division of Internal Medicine, University Hospital of North Norway, Tromsø, Norway
                [ ]Tromsø Endocrine Research Group, Department of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, Norway
                [ ]MRC Lifecourse Epidemiology Unit, Southampton, UK
                [ ]Victoria University, Wellington, New Zealand
                Article
                20
                10.1186/s13102-015-0020-y
                4641333
                26561526
                ea9f62c8-222c-4a70-85f0-c29f8f63ac3e
                © Christoffersen et al. 2015

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                History
                : 29 June 2015
                : 3 November 2015
                Categories
                Research Article
                Custom metadata
                © The Author(s) 2015

                population-based study,physical activity,adolescents,bone mineral density,dxa

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