The arm span to height relationship and its health implications

Abstract

The Roman architect, Vitruvius, had noted in the first century BC that the arm span closely approximated to height. This relationship has been exploited by medical science by using arm span to estimate height in situations where height measurement is not possible. This can be done by directly substituting height with arm span, a fixed ratio, or specific regression equations. It has also been noted that height decreases with increasing age due to physiological changes, degenerative changes and osteoporosis, while the arm span remains unchanged. The arm span-height difference (AHD) or arm span to height ratio (AHR) can therefore be used as a marker for age-related loss of height. Several studies have also investigated AHD as a predictor for osteoporosis-related vertebral fracture, due to the association of vertebral fractures with height loss. These studies have however yielded conflicting results, probably due to the lack of an agreed definition for vertebral fractures. A recent study demonstrated that AHR is inversely correlated with lung airflow volumes measured with spirometry, and directly correlated with severity of shortness of breath. By using AHR as a quantitative index for loss of height, the authors were able to demonstrate that loss of height is associated with breathing difficulties. The reduction in height with ageing may also result in underestimation of the severity of lung airflow problems and nutritional problems. Involving arm span measurements in the calculation of predicted lung airflow volumes and body mass index may potentially be the solution to overcoming this problem.