Sib Resemblance in Bone, Muscle and Fat Measurements of the Human Calf

Summary Separate measurements of bone, muscle and fat at ages up to 5 have been made from calf X‐rays of 120 pairs of sibs attending the Oxford Child Health Survey. The degree of sib resemblance in these measurements and in external calf circumference is found to be high, particularly when allowance is made for unavoidable errors of measurement. Sib resemblance in respect of muscle breadth increases with age, while for fat thickness it appears to decrease. In the case of muscle there is some evidence that fluctuations in growth as well as the average rate of growth are genetically controlled. There is no evidence of sex‐linkage. Correlation between different tissues in the same child is negligible. Assessments of skeletal maturity show a moderate correlation with bone diameter, but little association with muscle and none with fat. The amount of measurable sib resemblance is greater when these tissues are examined separately than when they are considered in relation to one another. The Oxford Child Health Survey was launched by the late Prof. John Ryle with assistance from the Medical Research Council; in recent years it has been directed by Dr A. M. Stewart. I am greatly indebted to Dr C. K. Westropp and Dr J. Parfit who were responsible for the clinical work of the survey, to Miss E. Roberts and Miss M. Barnes who took all the X‐rays, to Drs R. M. Acheson, L. Mynors and E. Jefferson who made the assessments of skeletal maturity and to Dr J. M. Tanner for criticisms of the draft.