Final answer:
True, air retained in the lungs during underwater weighing increases buoyancy and can overstate body fat estimations since it affects body density calculations.
Step-by-step explanation:
True, air that is not exhaled underwater increases the buoyancy of the body and can lead to an overestimation of body fat when using hydrostatic weighing to determine body density. During hydrostatic weighing, the volume of the body increases with the volume of air inhaled, which in turn, decreases the body's average density due to air's lower density compared to the body.
This is why, in methods such as the ones described in Figure 11.22 and Figure 11.27, the subject is instructed to completely empty their lungs and hold a metal weight to sink properly, allowing for a more accurate measurement of body density and subsequent calculation of percent body fat. The buoyant force, as explained, is influenced by both the submerged volume of the body and the density of the fluid.