Human metabolic allometry from basal to maximal ambulatory states, including load carriage and its distribution

Whole-body metabolic rate is strongly linked with body size, as it is primarily determined by both the number of cells within the body and their tissue-specific metabolic rates. For these reasons alone there will always be some inter-individual variations in metabolism, at any given metabolic intensity. While variations in body mass can explain the majority of these differences between individuals, it still remains difficult to remove the effect of body mass from metabolic data, as the relationship between both variables does not scale by a one-to-one ratio. Accordingly, the ubiquitous mass-normalisation approach is ineffective at this task (mL.kg-1.min-1). Therefore, an alternative scaling method was required so that metabolic rate can be both described and analysed with minimal error. In animals, basal metabolic rate scales by a non-linear, allometric regression against body body mass, and can be described using the body-mass exponent, mass 0.67. However, in humans, the nature1 of the scaling relationship remains unconfirmed, with both linear (first-order polynomial) and non-linear (allometric) scaling approaches used by researchers. An often overlooked issue with this situation is that the predictive error between both models increases as the mass range widens. Accordingly, the primary aim within this series of investigation was to determine which scaling model was more appropriate to describe the relationship between metabolic rate and body mass in humans..