Deriving an optimal threshold of waist circumference for detecting cardiometabolic risk in sub-Saharan Africa.

BACKGROUND: Waist circumference (WC) thresholds derived from western populations continue to be used in sub-Saharan Africa (SSA) despite increasing evidence of ethnic variation in the association between adiposity and cardiometabolic disease and availability of data from African populations. We aimed to derive a SSA-specific optimal WC cut-point for identifying individuals at increased cardiometabolic risk. METHODS: We used individual level cross-sectional data on 24 181 participants aged ⩾15 years from 17 studies conducted between 1990 and 2014 in eight countries in SSA. Receiver operating characteristic curves were used to derive optimal WC cut-points for detecting the presence of at least two components of metabolic syndrome (MS), excluding WC. RESULTS: The optimal WC cut-point was 81.2 cm (95% CI 78.5-83.8 cm) and 81.0 cm (95% CI 79.2-82.8 cm) for men and women, respectively, with comparable accuracy in men and women. Sensitivity was higher in women (64%, 95% CI 63-65) than in men (53%, 95% CI 51-55), and increased with the prevalence of obesity. Having WC above the derived cut-point was associated with a twofold probability of having at least two components of MS (age-adjusted odds ratio 2.6, 95% CI 2.4-2.9, for men and 2.2, 95% CI 2.0-2.3, for women). CONCLUSION: The optimal WC cut-point for identifying men at increased cardiometabolic risk is lower (⩾81.2 cm) than current guidelines (⩾94.0 cm) recommend, and similar to that in women in SSA. Prospective studies are needed to confirm these cut-points based on cardiometabolic outcomes.International Journal of Obesity advance online publication, 31 October 2017; doi:10.1038/ijo.2017.240.

A technique for studying the kinematics of human joints. Part I: Theory.

A novel analytical method that allows iterative synthesis and analysis of the structure and physiology of human joints from a kinematic viewpoint is presented. The technique may be used for both anatomical and physiological joints. The joints are modeled as contacting rigid bodies connected by muscles and ligaments. The muscles and ligaments are regarded as flexible connections, either connecting the articulating bones or acting across the joints. A taut ligament or muscle is converted to a constraining force on the moving bone and used with the geometry of the bone in determining the degrees of freedom of the joint. The method uses a unique approach of measuring coordinates of points from a coordinate system local to each bone to avoid compounding errors. It is shown how these could then be used with the measured or estimated maximum lengths of the flexible connections to predict such kinematic joint properties as type, mobility, and range of motion in an iterative manner.

A technique for studying the kinematics of human joints. Part II: The humeroscapular joint.

The humeroscapular joint is used as an example to illustrate some aspects of an analytical technique for studying the kinematics of human joints. Coordinates of attachment points for muscles and ligaments on the humerus and scapula of a human skeleton were measured on an automated coordinate measuring machine. Coordinates of points on the contact areas between the glenoid cavity and the humeral head were measured to determine and ensure the sphericity of the joint. Muscle and ligament lengths were also measured on a cadaver of similar dimensions to the skeleton. The data were then used to determine the range of motion of the humeroscapular joint by considering the intersections of spheres mapped onto a plane. It is shown that the glenohumeral ligament limits flexion while the coracohumeral ligament and supraspinatus muscle limit abduction. It is also shown that the coracoacromial ligament does not limit the motion of the humerus before the scapula gets involved in the motion of the shoulder complex.