Effects of lifetime loading history on cortical bone density and its distribution in middle-aged and older men

We have reported previously that long-term participation of weight-bearing exercise is associated with increased QCT-derived cortical bone size and strength in middle-aged and older men, but not whole bone cortical volumetric BMD. However, since bone remodeling and the distribution of loading-induced strains within cortical bone are non-uniform, the aim of this study was to examine the effects of lifetime loading history on cortical bone mass distribution and bone shape in healthy community dwelling middle-aged and older men. We used QCT to assess mid-femur and mid-tibia angular bone mass distribution around its center (polar distribution), the bone density distribution through the cortex (radial distribution), and the ratio between the maximum and minimum moments of inertia (I_max/I_min ratio) in 281 men aged 50 to 79 years. Current (> 50 years) and past (13–50 years) sport and leisure time activity was assessed by questionnaire to calculate an osteogenic index (OI) during adolescence and adulthood. All men were then categorized into a high (H) or low/non impact (L) group according to their OI scores in each period. Three contrasting groups were then formed to reflect weight-bearing impact categories during adolescence and then adulthood: H–H, H–L and L–L. For polar bone mass distribution, bone deposition in the anterolateral, medial and posterior cortices were 6–10% greater at the mid-femur and 9–24% greater at mid-tibia in men in the highest compared to lowest tertile of lifetime loading (p < 0.01– < 0.001). When comparing the influence of contrasting loading history during adolescence and adulthood, there was a graded response between the groups in the distribution of bone mass at the anterior-lateral and posterior regions of the mid-tibia (H–H > H–L > L–L). For radial bone density distribution, there were no statistically significant effects of loading at the mid-femur, but a greater lifetime OI was associated with a non-significant 10–15% greater bone density near the endocortical region of the mid-tibia. In conclusion, a greater lifetime loading history was associated with region-specific adaptations in cortical bone density.

Using social network analysis to identify key child care center staff for obesity prevention interventions: a pilot study

Introduction. Interest has grown in how systems thinking could be used in obesity prevention. Relationships between key actors, represented by social networks, are an important focus for considering intervention in systems. Method. Two long day care centers were selected in which previous obesity prevention programs had been implemented. Measures showed ways in which physical activity and dietary policy are conversations and actions transacted through social networks (interrelationships) within centers, via an eight item closed-ended social network questionnaire. Questionnaire data were collected from (17/20; response rate 85%) long day care center staff. Social network density and centrality statistics were calculated, using UCINET social network software, to examine the role of networks in obesity prevention. Results. “Degree” (influence) and “betweeness” (gatekeeper) centrality measures of staff inter-relationships about physical activity, dietary, and policy information identified key players in each center. Network density was similar and high on some relationship networks in both centers but markedly different in others, suggesting that the network tool identified unique center social dynamics. These differences could potentially be the focus of future team capacity building. Conclusion. Social network analysis is a feasible and useful method to identify existing obesity prevention networks and key personnel in long day care centers.