Body composition - what is measurable?

In 1878 Behnke noted that 'nothing is measured with greater error than the human body'. Over the intervening period measurement techniques have been developed which range from the relatively simple anthropometric methods to those based on sophisticated radiation and nuclear physics technologies. Nevertheless, despite the undoubted progress, it is important that we ask ourselves whether Behnke's observation might still have some validity. Many reviews have concentrated on the problems and limitations of given techniques with particular emphasis on achievable precision (because precision is easy to measure). However a straight-forward analysis of published data, especially of that relating to indirect techniques, shows that measurement precision is frequently small in magnitude compared to biological precision, the latter being simply a reflection of Nature's refusal to conform to imposed regression relationships. In this paper the body composition technologies are reviewed in the context of achievable accuracy and precision.