EXSS2021 Lecture Notes - Lecture 1: Body Composition, Hydrostatic Weighing, Skin Fold
4 Sep 2018
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2 component models: fat mass (fm) - anhydrous, no potassium, fat free mass (ffm) - 73% water content, 68. 1mmol. kg potassium. Measures: body density (bd) - via underwater weighing or hydrodensitometry, total body water (tbw) - via isotope dilution, total body potassium (tbk) - via gamma counter (most ffm made up of potassium) When a body is immersed in water it is buoyed up by a force which is equivalent to the weight of the volume of water displaced. Used to weigh a body underwater (hydrodensitometry) Density = mass of body in air / mass in air - mass in water (in grams) Measure can be affected by temperature of water, residual lung volume (subject must be maximally expired) Air displacement used (plesythmyograph) - how much volume body takes up in the pod. Determines volume -> density by measuring changes in pressure: calibrate pod, take air weight of person, place subject in pod, take measurements.
