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

Abstract

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.

Effects of a Specialist-Led, School Physical Education Program on Bone Mass, Structure, and Strength in Primary School Children: A 4-Year Cluster Randomized Controlled Trial

“…(3) However, of the four school-based exercise interventions that used pQCT to assess bone geometry, all failed to observe any significant exercise-induced benefits on measures of tibial bone structure, (6,(26)(27)(28) which may relate to the relatively short duration of these trials (9 to 16 months). In contrast, we observed that our 4-year generalized PE program focusing on core movements, coordination and agility, skill activities, movement challenges and games, and dynamic movement control improved midshaft cortical area and/or thickness in young girls and boys, but this did not translate into greater gains in bone strength.…”

“…Scans were analyzed using Stratec software, version 6. For distal sites, the periosteal surface of the radius/tibia metaphysis was found by a contour algorithm based on thresholding at 180 mg/cm 3 . BMC (g/cm of slice thickness), total bone area (ToA, mm 2 ), and total bone volumetric density (ToD, mg/cm 3 ) were determined.…”

“…Because the determination of CoD is affected by partial volume effect when CoTh is <2.5 mm, (16) adjustment was made for CoTh when analyzing CoD as described (17) (see also Statistical Analysis). Polar bone stress strain index (SSIpol, mm 3 ) was calculated to estimate diaphyseal bone resistance to bending and torsion. At the midshaft site only, muscle cross-sectional areas (CSA) were measured.…”

“…(3,5) With the introduction of more advanced imaging tools such as peripheral quantitative computed tomography (pQCT) that can provide a three-dimensional assessment of bone, there is also evidence that targeted weight-bearing impact exercise programs in children can improve bone structure (cross-sectional area and/or cortical thickness) and estimates of bone strength at loaded sites. (3,6,7) Collectively these findings provide important information about what can be achieved with targeted bone loading programs, but whether more generalized PA opportunities within the physical education (PE) curriculum offered to all school-aged children can enhance bone structure and strength remains uncertain.…”

Bone Densitometry in Children and Adolescents

“…7,36 Weight-bearing activity should be encouraged, and even short periods of high-intensity exercise (eg, jumping 10 minutes/ day, 3 times/week) have produced measurable gains in bone mass. 38 The childhood and teenage years appear to be of particular importance for bone accretion. The Iowa Bone Development Study (a prospective cohort study) showed 10% to 16% greater hip BMC and 8% greater hip areal BMD in participants who accumulated the greatest amount of activity from childhood through adolescence (12-year follow-up).…”