Development of an underwater weighing system for determining body composition.

A system was developed to reduce some of the difficulties associated with hydrostatic (underwater) weighing, specifically the need for complete exhalation and the subjective approximation of weighing scale measurements. The exhalation portion of the weighing protocol is particularly difficult for many disabled individuals and has contributed to the lack of available body composition information for this population. The components of our system include a computer system, load cell, spirometer, breathing tube, logic and signal conditioning circuitry specially constructed for this system, and a software package developed for this project. In a preliminary test, the body fat percentages of fourteen subjects (six males and eight females, ages 21-32 years) were determined both with the standard method and with our system. A correlation of r = 0.967 was found between the two methods, with our system's precision ranging from 1.0 to 1.3 body fat percentage points. The system could be used, for example, in developing a database for monitoring an individual's fitness or for making comparisons between groups (such as athlete to non-athlete).