PURPOSE: The Bod Pod uses air-displacement plethysmography to estimate body fat percentage (BF%). This study was designed to assess the test-retest reliability of the Bod Pod. METHODOLOGY: The study included 283 women (M age = 41.0 yr., SD = 3.0). Each participant was tested at least twice in the Bod Pod. Results showed no significant mean difference between the test and the retest. The intraclass correlation coefficient (ICC) was .991. However, the absolute value of the initial trial differences (absolute mean difference) was .96 (SD = .90). A third assessment of BF% was taken when the initial trial difference was greater than 1 percentage point, and the two closest values were compared. RESULTS: This strategy resulted in a significant decrease in the absolute mean difference, from .96 to .55 percentage point, and ICC increased to .998. CONCLUSIONS: The Bod Pod appears to measure body fat percentage reliably; however, findings suggest that multiple trials may be necessary to detect small treatment effects. Reliability of air displacement plethysmography.

To investigate the time course and mechanism of the increase in blood volume (BV) during isotonic exercise training, blood hemoglobin, hematocrit, and plasma volume (PV), osmotic, electrolyte, renin activity (PRA), vasopressin (AVP), and protein fractions were measured periodically in eight trained men 20-22 yr (Vo2max = 57 ml . min-1 . kg-1) before, during, and after ergometer exercise training (approximately 160 W, 65% Vo2max) for 2 h/day for 8 days. During training, plasma total osmolar and albumin contents increased to maintain a constant plasma osmolality and protein concentration during PV expansion. After training, BV increased by 457 ml (+8.1% P less than 0.05), due to an increase in PV of 427 ml (+12.1%, P less than 0.05); red cell volume was essentially constant (delta = +30 ml, NS). Plasma hypervolemia during training was associated with two major factors: 1) a ninefold elevation in PRA and AVP during exercise that facilitated Na+ and H2O retention, and 2) a progressive, chronic increase in plasma albumin content that provided increased H2O-binding capacity for the blood. Thus an efficient procedure for increasing PV is the daily performance of high-intensity isotonic leg exercise (65% Vo2max) for 2 h/day.

Plasma volume (PV), renin activity (PRA), and osmotic (Osm), sodium (Na+), and arginine vasopressin (AVP) concentrations were measured in venous blood samples taken before and after three levels of cycle ergometer exercise (100, 175, and 225 W) in 15 young male volunteers. Plasma volume and solute concentrations changed significantly (P less than 0.05, denoted by *) with work intensity. The % delta PV was -3.7%* at 100 W, -8.8%* at 175 W, and -12.4%* at 225 W. Plasma Na+ concentration, Osm, and AVP increase were curvilinear with graded exercise and were significant only when work intensity exceeded 40% VO2max. PRA increase was linear and significant at all work levels. The % delta PV was significantly correlated with delta Osm (r = 0.99*) and delta Na+ (r = 0.89*) but had low correlations with delta AVP (r = 0.22, NS) and delta PRA (r = 0.12, NS). However, delta AVP was significantly correlated with delta Na+ (r = 0.86*) and delta Osm (r = 0.83*), whereas delta PRA had low correlations with delta Na+ (r = 0.33, NS), delta Osm (r = 0.29, NS), and delta AVP (r = 0.43, NS). The data support the hypothesis that a) with exercise, AVP release is a primary factor for fluid and electrolyte regulation as it is highly correlated with the plasma hyperosmolality produced by a net hypotonic plasma efflux; b) an exercise intensity greater than 40% VO2max is required to change plasma osmolality and, thus, stimulate significant AVP release; and c) the stimulation of the renin-angiotensin system is a more general stress response, which responds to increasing sympathetic nervous activity.

The BOD POD, a new air-displacement plethysmograph for measuring human body composition, utilizes the inverse relationship between pressure and volume (Boyle's law) to measure body volume directly. The quantity of air in the lungs during tidal breathing, the average thoracic gas volume (Vtg), is also measured by the BOD POD by using a standard plethysmographic technique. Alternatively, the BOD POD provides the use of a predicted Vtg (Vtgpred). The validity of using Vtgpred in place of measured Vtg (Vtgmeas) to determine the percentage of body fat (%BF) was evaluated in 50 subjects (36 women, 14 men; ages 18-56 yr). There was no significant difference between Vtgmeas and Vtgpred (mean difference +/- SE, 53.5 +/- 63.3 ml) nor in %BF by using Vtgmeas vs. Vtgpred (0.2 +/- 0.2 %BF). On an individual basis, %BF measured by using Vtgmeas vs. Vtgpred differed within +/-2.0% BF for 82% of the subjects; maximum differences were -2.9 to +3.0% BF. For comparison, data from 24 subjects who had undergone hydrostatic weighing were evaluated for the validity of using predicted vs. measured residual lung volume (VRpred vs. VRmeas, respectively). Differences between VRmeas and VRpred and in %BF calculated by using VRmeas vs. VRpred were significant (187 +/- 46 ml and 1.4 +/- 0.3% BF, respectively; P < 0.001). On an individual basis, %BF determined by using VRmeas vs. VRpred differed within +/-2.0% BF for 46% of the subjects; maximum differences were -2.9 to +3.8% BF. With respect to %BF measured by air displacement, our findings support the use of Vtgpred for group mean comparisons and for purposes such as screening in young to middle-aged individuals. This contrasts with the use of VRpred in hydrostatic weighing, which leads to significant errors in the estimation of %BF. Furthermore, although the use of Vtgpred has some application, determining Vtgmeas is relatively simple in most cases. Therefore, we recommend that the use of Vtgmeas remain as standard experimental and clinical practice.

The purpose was to test the hypothesis that twice daily, short-term, variable intensity isotonic and intermittent high-intensity isokinetic leg exercise would maintain peak O2 uptake (VO2) and muscular strength and endurance, respectively, at or near ambulatory control levels during 30 days of -6 degrees head-down bed rest (BR) deconditioning. Nineteen men (aged 32-42 yr) were divided into no exercise control (peak VO2 once/wk, n = 5), isokinetic (Lido ergometer, n = 7), and isotonic (Quinton ergometer, n = 7) groups. Exercise training was conducted in the supine position for two 30-min periods/day for 5 days/wk. Isotonic training was at 60-90% of peak VO2, and isokinetic training (knee flexion-extension) was at 100 degrees/s. Mean (+/- SE) changes (P less than 0.05) in peak VO2 (ml.m-1.kg-1) from ambulatory control to BR day 28 were 44 +/- 4 to 36 +/- 3, -18.2% (3.27-2.60 l/m) for no exercise, 39 +/- 4 to 40 +/- 3, +2.6% (3.13-3.14 l/min) for isotonic, and 44 +/- 3 to 40 +/- 2, -9.1% (3.24-2.90 l/min) for isokinetic. There were no significant changes in any groups in leg peak torque (right knee flexion or extension), leg mean total work, arm total peak torque, or arm mean total work. Mean energy costs for the isotonic and isokinetic exercise training were 446 kcal/h (18.8 +/- 1.6 ml.min-1.kg-1) and 214 kcal/h (8.9 +/- 0.5 ml.m-1.kg-1), respectively. Thus near-peak, variable intensity, isotonic leg exercise maintains peak VO2 during 30 days of BR, while this peak, intermittent, isokinetic leg exercise protocol does not.