Validity and reliability of body composition techniques in healthy adults

The purpose of this investigation was to assess the day-to-day and week-to-week reliability of body fat (BF%) measurements using three different methods [air displacement plethysmography (Bod Pod), bioelectrical impedance analysis (Fitbit Aria®), and hydrostatic weighing (HW)] in the San Francisco State University Exercise Physiology Laboratory. Additionally, the validity of BF% measurements using the Bod Pod and Fitbit Aria® were compared to the industry “gold standard” of HW. Twenty-two males and 21 females (age: 27.9 ± 5.6 years) participated in the three-day investigation. Each day, participants completed BF% measurements via Bod Pod, Aria® scale [‘Lean’ (Al) and ‘Regular’ (Ar) modes], and HW. The Bod Pod was found to be a valid method for measuring BF% in all participants (0.4±4.3%; SEE=2.2%); however when analyzed by sex, it was valid for females (-0.3±4.0%; SEE=2.0%) but significantly over estimated males (1.0±4.3%; SEE=2.2%). Ar agreed with HW when analyzing BF% for all participants (-0.8±9.3%; SEE=4.4%) and females (0.4±10.8%; SEE=4.4%), but significantly underestimated males (-2.0±7.1%; SEE=3.7%). Al underestimated BF% by -5±9.1% (SEE=4.2%) for all participants (males: -7.9±6.9%; females: -2.6±8.0%; p<0.05), and this discrepancy was more pronounced in males. Overall, the “mode” chosen on the Aria® scale greatly impacts validity of female participants, but was not valid for males using Al or Ar. All methods were reliable when comparing day-to-day and week-to-week BF% measurements for all groups, suggesting the Fitbit Aria® can be a reliable at-home body composition analysis scale.