up to 4.2% of body fat. Moderate exercise before BIA measurements lead to an overestimation of fat-free mass and an underestimation of body fat percentage due to reduced impedance. For example, moderate intensity exercise for 90–120 minutes before BIA measurements causes nearly a 12 kg overestimation of fat-free mass, i.e. body fat is significantly underestimated. Therefore, it is recommended not to perform BIA for several hours after moderate or high intensity exercise. BIA is considered reasonably accurate for measuring groups, of limited accuracy for tracking body composition in an individual over a period of time, but is not considered sufficiently accurate for recording of single measurements of individuals. Consumer grade devices for measuring BIA have not been found to be sufficiently accurate for single measurement use, and are better suited for use to measure changes in body composition over time for individuals. The two-electrode, e.g., foot-to-foot or hand-to-hand measurement, is generally found to be less accurate than 4-electrode (tetra-polar technique in which the current circuit is provided by a pair of distal electrodes with impedance measured, as the voltage drop between a separate pair of proximal electrodes) methods. Multiple electrodes, typically eight, may be used located on the hands and feet allowing measurement of the impedance of the individual body segments - arms, legs and torso. The advantage of the multiple electrode devices is that body segments may be measured simultaneously without the need to relocate electrodes. Results for some impedance instruments tested found poor limits of agreement and in some cases systematic bias in estimation of visceral fat percentage, but good accuracy in the prediction of resting energy expenditure (REE) when compared with more accurate whole-body magnetic resonance imaging (MRI) and dual-energy X-ray absorptiometry (DXA). Impedance is frequency sensitive; at low frequency the electric current flows preferentially through extracellular water (ECW) only while at high frequency the current can cross cell membranes and hence flows through total body water (TBW). In bioimpedance spectroscopy devices (BIS) resistance at zero and infinite frequency can be estimated and, at least theoretically, should provide the optimal predictors of ECW and TBW and hence body fat-free mass respectively. In practice, the improvement in accuracy is marginal. The use of multiple frequencies or BIS in specific BIA devices has been shown to have high correlation with DXA when measuring body fat percentage. The correlation with DXA can be as high as 99% when measuring fat-free