A First-Principles Theory of the Human Body: The Chaos of Indices

This preprint reviews anthropometric indices and related body-measurement methods as scalar mappings from measured body variables to numerical outputs. It analyzes BMI as a dimensional reduction based on body mass and height that omits transverse body geometry, producing information loss: physically distinct body configurations may share the same scalar value. The article compares historically important anthropometric formulas, body-shape indices, body-composition equations, and instrumental methods with respect to their input variables, mathematical form, physical dimensions, geometric degrees of freedom, and intended use. It argues that the proliferation of anthropometric indices reflects the absence of a common physical referent linking body mass, body volume, shape, and density. Opening paper in the research series A First-Principles Theory of the Human Body. Series repository: Open Science Framework, DOI: https://doi.org/10.17605/OSF.IO/ENAUQ.