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      Longitudinal Trajectories of Television Watching Across Childhood and Adolescence Predict Bone Mass at Age 20 Years in the Raine Study : TELEVISION WATCHING IN CHILDHOOD/ADOLESCENCE PREDICTS BONE MASS AT AGE 20

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      Journal of Bone and Mineral Research
      Wiley-Blackwell

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          Bone mineral accrual from 8 to 30 years of age: an estimation of peak bone mass.

          Bone area (BA) and bone mineral content (BMC) were measured from childhood to young adulthood at the total body (TB), lumbar spine (LS), total hip (TH), and femoral neck (FN). BA and BMC values were expressed as a percentage of young-adult values to determine if and when values reached a plateau. Data were aligned on biological ages [years from peak height velocity (PHV)] to control for maturity. TB BA increased significantly from -4 to +4 years from PHV, with TB BMC reaching a plateau, on average, 2 years later at +6 years from PHV (equates to 18 and 20 years of age in girls and boys, respectively). LS BA increased significantly from -4 years from PHV to +3 years from PHV, whereas LS BMC increased until +4 from PHV. FN BA increased between -4 and +1 years from PHV, with FN BMC reaching a plateau, on average, 1 year later at +2 years from PHV. In the circumpubertal years (-2 to +2 years from PHV): 39% of the young-adult BMC was accrued at the TB in both males and females; 43% and 46% was accrued in males and females at the LS and TH, respectively; 33% (males and females) was accrued at the FN. In summary, we provide strong evidence that BA plateaus 1 to 2 years earlier than BMC. Depending on the skeletal site, peak bone mass occurs by the end of the second or early in the third decade of life. The data substantiate the importance of the circumpubertal years for accruing bone mineral. Copyright © 2011 American Society for Bone and Mineral Research.
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            Three rules for bone adaptation to mechanical stimuli.

            The primary mechanical function of bones is to provide rigid levers for muscles to pull against, and to remain as light as possible to allow efficient locomotion. To accomplish this bones must adapt their shape and architecture to make efficient use of material. Bone adaptation during skeletal growth and development continuously adjusts skeletal mass and architecture to changing mechanical environments. There are three fundamental rules that govern bone adaptation: (1) It is driven by dynamic, rather than static, loading. (2) Only a short duration of mechanical loading is necessary to initiate an adaptive response. (3) Bone cells accommodate to a customary mechanical loading environment, making them less responsive to routine loading signals. From these rules, several mathematical equations can be derived that provide simple parametric models for bone adaptation.
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              Relationship between young peoples' sedentary behaviour and biomedical health indicators: a systematic review of prospective studies.

              The aim of this systematic review was to describe the prospective relationship between childhood sedentary behaviour and health indicators. We identified prospective studies from searches in PubMed, EMBASE, PsycInfo and Cochrane, from January 1989 through April 2010. Two reviewers independently screened the titles and abstracts for eligibility, rated the methodological quality of the studies, and extracted data. We identified 31 papers, examining 27 different cohorts. The quality score of the studies ranged from 38 to 88%. Nine studies were scored as high quality. According to the best evidence synthesis we found insufficient evidence for a longitudinal positive relationship between 'sedentary time'- mainly TV viewing - and body mass index (BMI) and more specific indicators of fat mass. One high quality and two low quality studies found a significant inverse relationship between sedentary time - mainly TV viewing - and aerobic fitness, leading to moderate evidence for this inverse relationship. There was insufficient evidence for a longitudinal relationship between sedentary time and blood pressure, blood lipids or bone mass. Our systematic review suggests that there is moderate evidence for a longitudinal inverse relationship between screen time and aerobic fitness during childhood. Thus there is evidence to limit screen time in young people in order to prevent low levels of fitness. The possible detrimental health effects of prolonged or excessive sitting on other health indicators needs further study. © 2011 The Authors. obesity reviews © 2011 International Association for the Study of Obesity.
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                Author and article information

                Journal
                Journal of Bone and Mineral Research
                J Bone Miner Res
                Wiley-Blackwell
                08840431
                November 2016
                November 2016
                : 31
                : 11
                : 2032-2040
                Article
                10.1002/jbmr.2890
                27378122
                9dd45756-58d1-4177-8259-f2805112d6fe
                © 2016

                http://doi.wiley.com/10.1002/tdm_license_1.1

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