Final answer:
True, exhaling to residual volume is necessary for an accurate body fat measurement in Bod Pod or hydrostatic weighing, to correct for the effect of residual air on the body's buoyancy and resulting density calculations.
Step-by-step explanation:
Exhaling to residual volume is indeed necessary to obtain an accurate measure of body fat when using devices like Bod Pod or hydrostatic weighing. The process is necessary because any remaining air in the lungs would affect the body's buoyancy and subsequently the accuracy of the body density calculation. The residual volume (RV), which is the amount of air left in the lungs after a maximal exhalation, is always present to prevent the lung tissues from sticking together and to keep gas concentrations stable. To ensure the accuracy of these measurements and the calculation of percent body fat, corrections must be made for the residual air in the lungs as well as any weights used to assist in submersion during hydrostatic weighing.