Effect of exercise-induced changes in residual lung volume on the determination of body composition.

The transient increase in residual lung volume (RV) as a result of exercise has been well documented. An accurate assessment of exercise-induced RV would be important when hydrostatic weighing (HW) is performed after exercise. The purpose of this study was to determine whether accurate HW measures could be performed after exercise when changes in RV are measured. Subjects (n = 32) performed pulmonary function (vital capacity [VC]-estimated RV), oxygen dilution-determined RV, and HW measures before and after either a maximal treadmill test (n = 16) or seated rest (n = 16). Two-way analysis of variance (p </= 0.05) was performed on RV and HW body composition to identify significance between pre- and posttreatment. A post hoc paired t-test was performed to identify the source of any significant interactions. Results showed that for exercising subjects, oxygen dilution-determined RV was significantly increased between pre- and posttreatment. Estimated RV did not differ significantly for either group. Hydrostatic weighing body composition data were not significantly different for either group when oxygen dilution-determined RV was used. Conversely, when estimated RV was used in the calculation of body composition, a significant difference was noted between pre- and posttreatment in the exercise group (percentage of fat increased, whereas percentage of lean body mass decreased). The results of this study suggest that accurate body composition estimation can be performed after exercise. Body composition accuracy, however, is reliant on the concomitant employment of HW and RV estimation techniques that are sensitive to transient changes in RV. For this study, the oxygen dilution method of RV determination was used. Estimated RV (VC method) was not sensitive to changes in RV, subsequently resulting in erroneous HW body composition after maximal exercise.