Lindsay Nettlefold

A systematic review of the evidence for Canada's Physical Activity Guidelines for Adults

This systematic review examines critically the scientific basis for Canadas Physical Activity Guide for Healthy Active Living for adults. Particular reference is given to the dose-response relationship between physical activity and premature all-cause mortality and seven chronic diseases (cardiovascular disease, stroke, hypertension, colon cancer, breast cancer, type 2 diabetes (diabetes mellitus) and osteoporosis). The strength of the relationship between physical activity and specific health outcomes is evaluated critically. Literature was obtained through searching electronic databases (e.g., MEDLINE, EMBASE), cross-referencing, and through the authors knowledge of the area. For inclusion in our systematic review articles must have at least 3 levels of physical activity and the concomitant risk for each chronic disease. The quality of included studies was appraised using a modified Downs and Black tool. Through this search we identified a total of 254 articles that met the eligibility criteria related to premature all-cause mortality (N = 70), cardiovascular disease (N = 49), stroke (N = 25), hypertension (N = 12), colon cancer (N = 33), breast cancer (N = 43), type 2 diabetes (N = 20), and osteoporosis (N = 2). Overall, the current literature supports clearly the dose-response relationship between physical activity and the seven chronic conditions identified. Moreover, higher levels of physical activity reduce the risk for premature all-cause mortality. The current Canadian guidelines appear to be appropriate to reduce the risk for the seven chronic conditions identified above and all-cause mortality.

The challenge of low physical activity during the school day: at recess, lunch and in physical education

Purpose To describe physical activity (PA) intensity across a school day and assess the percentage of girls and boys achieving recommended guidelines. Methods The authors measured PA via accelerometry in 380 children (8–11 years) and examined data representing (1) the whole school day, (2) regular class time, (3) recess, (4) lunch and (5) scheduled physical education (PE). Activity was categorised as sedentary (SED), light physical activity (LPA) or moderate to vigorous physical activity (MVPA) using age-specific thresholds. They examined sex differences across PA intensities during each time period and compliance with recommended guidelines. Results Girls accumulated less MVPA and more SED than boys throughout the school day (MVPA −10.6 min; SED +13.9 min) recess (MVPA −1.6 min; SED +1.7 min) and lunch (MVPA −3.1 min; SED +2.9 min). Girls accumulated less MVPA (−6.2 min), less LPA (−2.5 min) and more SED (+9.4 min) than boys during regular class time. Fewer girls than boys achieved PA guidelines during school (90.9% vs 96.2%), recess (15.7% vs 34.1%) and lunch (16.7% vs 37.4%). During PE, only 1.8% of girls and 2.9% of boys achieved the PA guidelines. Girls and boys accumulated similar amounts of MVPA, LPA and SED. Conclusion The MVPA deficit in girls was due to their sedentary behaviour as opposed to LPA. Physical activity strategies that target girls are essential to overcome this deficit. Only a very small percentage of children met physical activity guidelines during PE. There is a great need for additional training and emphasis on PA during PE. In addition schools should complement PE with PA models that increase PA opportunities across the school day.

Influence of Physical Activity on Bone Strength in Children and Adolescents: A Systematic Review and Narrative Synthesis

A preponderance of evidence from systematic reviews supports the effectiveness of weight‐bearing exercises on bone mass accrual, especially during the growing years. However, only one systematic review (limited to randomized controlled trials) examined the role of physical activity (PA) on bone strength. Thus, our systematic review extended the scope of the previous review by including all PA intervention and observational studies, including organized sports participation studies, with child or adolescent bone strength as the main outcome. We also sought to discern the skeletal elements (eg, mass, structure, density) that accompanied significant bone strength changes. Our electronic‐database, forward, and reference searches yielded 14 intervention and 23 observational studies that met our inclusion criteria. We used the Effective Public Health Practice Project (EPHPP) tool to assess the quality of studies. Due to heterogeneity across studies, we adopted a narrative synthesis for our analysis and found that bone strength adaptations to PA were related to maturity level, sex, and study quality. Three (of five) weight‐bearing PA intervention studies with a strong rating reported significantly greater gains in bone strength for the intervention group (3% to 4%) compared with only three significant (of nine) moderate intervention studies. Changes in bone structure (eg, bone cross‐sectional area, cortical thickness, alone or in combination) rather than bone mass most often accompanied significant bone strength outcomes. Prepuberty and peripuberty may be the most opportune time for boys and girls to enhance bone strength through PA, although this finding is tempered by the few available studies in more mature groups. Despite the central role that muscle plays in bones response to loading, few studies discerned the specific contribution of muscle function (or surrogates) to bone strength. Although not the focus of the current review, this seems an important consideration for future studies.

Implementation of school based physical activity interventions: A systematic review

OBJECTIVEnImplementation science is an emerging area in physical activity (PA) research. We sought to establish the current state of the evidence related to implementation of school-based PA models to explore 1) the relationship between implementation and health outcomes, and 2) factors that influence implementation.nnnMETHODSnWe searched 7 electronic databases (1995-2014) and included controlled studies of school-based PA programmes for healthy youth (6-18 y) measuring at least one physical health-related outcome. For objective 1, studies linked implementation level to student-level health outcome(s). For objective 2, studies reported factors associated with implementation.nnnRESULTSnThere was substantial variability in how health outcomes and implementation were assessed. Few studies linked implementation and health outcomes (n=15 interventions). Most (11/15) reported a positive relationship between implementation and at least one health outcome. Implementation factors were reported in 29 interventions. Of 22 unique categories, time was the most prevalent influencing factor followed by resource availability/quality and supportive school climate.nnnCONCLUSIONSnImplementation evaluation supports scale-up of effective school-based PA interventions and thus population-level change. Our review serves as a call to action to 1) address the link between implementation and outcome within the school-based PA literature and 2) improve and standardize definitions and measurement of implementation.

A comparison of bone quality at the distal radius between Asian and white adolescents and young adults: An HR‐pQCT study

Paradoxically, Asians have lower areal bone mineral density (aBMD), but their rates of hip and wrist fractures are lower than whites. Therefore, we used high‐resolution pQCT (HR‐pQCT) to determine whether differences in bone macrostructure and microstructure, BMD, and bone strength at the distal radius were apparent in Asian (nu2009=u200991, 53 males, 38 females, [meanu2009±u2009SD] 17.3u2009±u20091.5 years) and white (nu2009=u200989, 46 males, 43 females, 18.1u2009±u20091.8 years) adolescents and young adults. HR‐pQCT outcomes included total BMD (Tt.BMD), trabecular bone volume fraction (BV/TV), and trabecular number (Tb.N), thickness (Tb.Th), and separation (Tb.Sp). We used an automated segmentation algorithm to determine total bone area (Tt.Ar), and cortical BMD (Ct.BMD), porosity (Ct.Po), and thickness (Ct.Th), and we applied finite element (FE) analysis to HR‐pQCT scans to estimate bone strength. We fit sex‐specific multivariable regression models to compare bone outcomes between Asians and whites, adjusting for age, age at menarche (girls), lean mass, ulnar length, dietary calcium intake, and physical activity. In males, after adjusting for covariates, Asians had 11% greater Tt.BMD, 8% greater Ct.BMD, and 25% lower Ct.Po than whites (pu2009<u20090.05). Also, Asians had 9% smaller Tt.Ar and 27% greater Ct.Th (pu2009<u20090.01). In females, Asians had smaller Tt.Ar than whites (16%, pu2009<u20090.001), but this difference was not significant after adjusting for covariates. Asian females had 5% greater Ct.BMD, 12% greater Ct.Th, and 11% lower Tb.Sp than whites after adjusting for covariates (pu2009<u20090.05). Estimated bone strength did not differ between Asian and white males or females. Our study supports the notion of compensatory elements of bone structure that sustain bone strength; smaller bones as observed between those of Asian origin compared with white origin have, on average, more dense, less porous, and thicker cortices. Longitudinal studies are needed to determine whether ethnic differences in bone structure exist in childhood, persist into old age, and whether they influence fracture risk.

Youth physical activity and the neighbourhood environment: Examining correlates and the role of neighbourhood definition

The primary objective of this study was to examine relationships between neighbourhood built and social environment characteristics and moderate to vigorous physical activity (MVPA) in a sample of children aged 8-11 in Vancouver, British Columbia and the surrounding lower mainland region (nxa0=xa0366). A secondary objective was to assess how neighbourhood definition influences these relationships, by using measures calculated at multiple buffer sizes: 200, 400, 800 and 1600xa0m (1xa0mile). Geographic information systems -software was used to create a broad set of measures of neighbourhood environments. Physical activity was measured objectively using accelerometers. Relationships between MVPA and neighborhood characteristics were assessed using generalized estimating equations to account for the clustering of children within schools. Sex specific relationships were assessed through sex stratified models. When controlling for child age, sex and ethnicity, MVPA was positively associated with commercial density, residential density, number of parks and intersection density; and negatively associated with distance to school and recreation sites. When entered as a composite index, these measures accounted for 4.4% in the variation in MVPA for the full sample (boys and girls). Sex stratified models better explained the relationships between neighbourhood environment and physical activity. For boys, built and social environment characteristics of neighbourhoods accounted for 8.7% of the variation in MVPA, and for girls, neighborhood factors explained 7.2% of the variation. Sex stratified models also point towards distinct differences in factors associated with physical activity, with MVPA of boys associated with wider ranging neighborhood characteristics than MVPA of girls. For girls, two safety-related neighbourhood features were found to be significantly associated with MVPA: cul-de-sac density and proportion of low speed limit streets. In all models, larger buffer sizes, and predominantly the largest buffer size, best explained environment-physical activity relationships.

Action Schools! BC implementation: from efficacy to effectiveness to scale-up

Objectives To describe Action Schools! BC (AS! BC) from efficacy to scale-up. Participants/setting Education and health system stakeholders and children in grades 4–6 from elementary schools in British Columbia, Canada. Intervention At the provincial level, the AS! BC model reflected socioecological theory and a partnership approach to social change. Knowledge translation and exchange were embedded as a foundational element. At the school level, AS! BC is a comprehensive school health-based model providing teachers and schools with training and resources to integrate physical activity (PA) and healthy eating (HE) into the school environment. Our research team partnered with key community and government stakeholders to deliver and evaluate AS! BC over efficacy, effectiveness and implementation trials. Results On the basis of significant increases in PA, cardiovascular fitness, bone and HE in AS! BC schools during efficacy trials, the BC government supported a provincial scale-up. Since its inception, the AS! BC Support Team and >225 trained regional trainers have delivered 4677 teacher-focused workshops (training approximately 81u2005000 teachers), reaching approximately 500u2005000 students. After scale-up, PA delivery was replicated but the magnitude of change appeared less. One (HE) and 4 (PA) years after scale-up, trained AS! BC teachers provided more PA and HE opportunities for students even in the context of supportive provincial policies. Conclusions Whole school models like AS! BC can enhance childrens PA and health when implemented in partnership with key stakeholders. At the school level, adequately trained and resourced teachers and supportive school policies promoted successful scale-up and sustained implementation. At the provincial level, multisectoral partnerships and embedded knowledge exchange mechanisms influenced the context for action at the provincial and school level, and were core elements of successful implementation. Trial registration number Clinical Trials Registry NCT01412203.

Physical Activity, Sedentary Time, and Bone Strength From Childhood to Early Adulthood: A Mixed Longitudinal HR-pQCT study

Bone strength is influenced by bone geometry, density, and bone microarchitecture, which adapt to increased mechanical loads during growth. Physical activity (PA) is essential for optimal bone strength accrual; however, less is known about how sedentary time influences bone strength and its determinants. Thus, our aim was to investigate the prospective associations between PA, sedentary time, and bone strength and its determinants during adolescence. We used HR‐pQCT at distal tibia (8% site) and radius (7% site) in 173 girls and 136 boys (aged 9 to 20 years at baseline). We conducted a maximum of four annual measurements at the tibia (nu2009=u2009785 observations) and radius (nu2009=u2009582 observations). We assessed moderate‐to‐vigorous PA (MVPA) and sedentary time with accelerometers (ActiGraph GT1M). We aligned participants on maturity (years from age at peak height velocity) and fit a mixed‐effects model adjusting for maturity, sex, ethnicity, leg muscle power, lean mass, limb length, dietary calcium, and MVPA in sedentary time models. MVPA was a positive independent predictor of bone strength (failure load [F.Load]) and bone volume fraction (BV/TV) at the tibia and radius, total area (Tt.Ar) and cortical porosity (Ct.Po) at the tibia, and negative predictor of load‐to‐strength ratio at the radius. Sedentary time was a negative independent predictor of Tt.Ar at both sites and Ct.Po at the tibia and a positive predictor of cortical thickness (Ct.Th), trabecular thickness (Tb.Th), and cortical bone mineral density (Ct.BMD) at the tibia. Bone parameters demonstrated maturity‐specific associations with MVPA and sedentary time, whereby associations were strongest during early and mid‐puberty. Our findings support the importance of PA for bone strength accrual and its determinants across adolescent growth and provide new evidence of a detrimental association of sedentary time with bone geometry but positive associations with microarchitecture. This study highlights maturity‐specific relationships of bone strength and its determinants with loading and unloading. Future studies should evaluate the dose‐response relationship and whether associations persist into adulthood.

Bone architecture and strength in the growing skeleton: the role of sedentary time.

PURPOSEnTodays youths spend close to 60% of their waking hours in sedentary activities; however, we know little about the potentially deleterious effects of sedentary time on bone health during this key period of growth and development. Thus, our objective was to determine whether sedentary time is associated with bone architecture, mineral density, and strength in children, adolescents, and young adults.nnnMETHODSnWe used high-resolution peripheral quantitative computed tomography (Scanco Medical) to measure bone architecture (trabecular and cortical microstructure and bone macrostructure) and cortical and total bone mineral density (BMD) at the distal tibia (8% site) in 154 males and 174 females (9-20 yr) who were participants in the University of British Columbia Healthy Bones III study. We applied finite element analysis to high-resolution peripheral quantitative computed tomography scans to estimate bone strength. We assessed self-reported screen time in all participants using a questionnaire and sedentary time (volume and patterns) in a subsample of participants with valid accelerometry data (89 males and 117 females; ActiGraph GT1M). We fit sex-specific univariate multivariable regression models, controlling for muscle cross-sectional area, limb length, maturity, ethnicity, dietary calcium, and physical activity.nnnRESULTSnWe did not observe independent effect of screen time on bone architecture, BMD, or strength in either sex (P > 0.05). Likewise, when adjusted for muscle cross-sectional area, limb length, maturity, ethnicity, dietary calcium, and physical activity, accelerometry-derived volume of sedentary time and breaks in bouts of sedentary time were not a determinant of bone architecture, BMD, or strength in either sex (P > 0.05).nnnCONCLUSIONSnFurther study is warranted to determine whether the lack of association between sedentary time and bone architecture, BMD, and strength at the distal tibia is also present at other skeletal sites.

Reexamining the Surfaces of Bone in Boys and Girls During Adolescent Growth: A 12-Year Mixed Longitudinal pQCT Study.

We revisit Stanley Garns theory related to sex differences in endocortical and periosteal apposition during adolescence using a 12‐year mixed longitudinal study design. We used peripheral quantitative computed tomography to examine bone parameters in 230 participants (110 boys, 120 girls; aged 11.0 years at baseline). We assessed total (Tt.Ar, mm2), cortical (Ct.Ar, mm2), and medullary canal area (Me.Ar, mm2), Ct.Ar/Tt.Ar, cortical bone mineral density (Ct.BMD, mg/cm3), and polar strength‐strain index (SSIp, mm3) at the tibial midshaft (50% site). We used annual measures of height and chronological age to identify age at peak height velocity (APHV) for each participant. We compared annual accrual rates of bone parameters between boys and girls, aligned on APHV using a linear mixed effects model. At APHV, boys demonstrated greater Tt.Ar (ratio = 1.27; 95% confidence interval [CI] 1.21, 1.32), Ct.Ar (1.24 [1.18, 1.30]), Me.Ar (1.31 [1.22, 1.40]), and SSIp (1.36 [1.28, 1.45]) and less Ct.Ar/Tt.Ar (0.98 [0.96, 1.00]) and Ct.BMD (0.97 [0.96, 0.97]) compared with girls. Boys and girls demonstrated periosteal bone formation and net bone loss at the endocortical surface. Compared with girls, boys demonstrated greater annual accrual rates pre‐APHV for Tt.Ar (1.18 [1.02, 1.34]) and Me.Ar (1.34 [1.11, 1.57]), lower annual accrual rates pre‐APHV for Ct.Ar/Tt.Ar (0.56 [0.29, 0.83]) and Ct.BMD (–0.07 [–0.17, 0.04]), and similar annual accrual rates pre‐APHV for Ct.Ar (1.10 [0.94, 1.26]) and SSIp (1.14 [0.98, 1.30]). Post‐APHV, boys demonstrated similar annual accrual rates for Ct.Ar/Tt.Ar (1.01 [0.71, 1.31]) and greater annual accrual rates for all other bone parameters compared with girls (ratio = 1.23 to 2.63; 95% CI 1.11 to 3.45). Our findings support those of Garn and others of accelerated periosteal apposition during adolescence, more evident in boys than girls. However, our findings challenge the notion of greater endocortical apposition in girls, suggesting instead that girls experience diminished endocortical resorption compared with boys.