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Air displacement plethysmography (ADP) is a popular method for estimating body density (Db). Most ADP tests are performed once, with test-retest investigations scarce. Therefore, we investigated test-retest reliability of ADP. Active men (n = 25) and women (n = 25) volunteered and followed standard pretest guidelines. Participants wore dry, form-fitting swimwear and manufacturer-supplied swim caps. In a single session, two ADP trials with measured thoracic gas volume (TGV) were performed without repositioning participants. Separate 2 (sex) × 2 (ADP trial) repeated-measures ANOVAs were performed to investigate within-between comparisons of Db, TGV, body volume (Vb), and relative fatness (%BF). Paired t tests were used to investigate significant differences as appropriate. The Bland and Altman technique was used to depict individual intertrial variations. For all analyses, α =.05. A significant main effect for sex was found; men were lower in %BF and higher in all other variables compared with women. Individual variability was notable (ADP1–ADP2). The range of individual intertrial differences were larger for women than men, respectively, for Db (-0.0096–0.0045 g/cc; -0.0019–0.0054 g/cc), TGV (-0.623–1.325 L; -0.584–0.378 L), Vb (-0.249–2.10 L; -0.234–0.397 L), and %BF (-2.1–4.4%; -0.2–0.9%). When assessing body composition of women via ADP or using Db from ADP in a multicomponent model, at least two trials with measured TGV should be performed and the average of the values recorded and reported.

This study assessed the predictive accuracy of a new hand-held, segmental, bioimpedance (BI) analyzer in estimating the relative body fat (%BF) of a sample of 25 men and 23 women (18–55 years, 7.0 to 42.8%BF_HW). The reference method was hydrostatic weighing (HW) at residual lung volume. The %BF estimates obtained from manufacturer’s (Omron) gender-specific equations were cross-validated. There were high validity coefficients ( $r_{y,y^{\prime }}=.91$ and .83, for men and women, respectively), moderate prediction errors (SEE = 3.46%, E = 3.64%BF for men; SEE = 4.04%, E = 3.87%BF for women), and no significant difference (p >.05) between the average ${\%\text{BF}}_{\text{HW}}$ and ${\%\text{BF}}_{\text{Omron}}$ for women (21.8% vs. 2I.6%BF, respectively). For men, there was a small but significant (p < .05) difference in ${\%\text{BF}}_{\text{HW}}$ (18.7%) and ${\%\text{BF}}_{\text{Omron}}$ (20.1 %). For both men and women, the line of identity did not differ significantly (p > .05) from the line of best fit. The Omron® BI equations accurately estimated the %BF of 72% of the men and 65% of the women in this sample within ±3.5%BF. Therefore, use of the Omron® BI analyzer is suitable for assessing the %BF of adults having demographic characteristics similar to those of this sample.

The BodPod® (COSMED, Concord, CA) uses predicted (pTGV) or measured thoracic gas volume (mTGV) during estimations of percentage body fat (%BF). In young adults, there is inconsistent evidence on the variation between pTGV and mTGV, and the effect of sex as a potential covariate on this relationship is unknown. This study examined the difference between TGV assessments and its effect on %BF and potential sex differences that may impact this relationship. A retrospective analysis of BodPod® pTGV and mTGV for 95 men and 86 women ages 18–30 years was performed. Predicted TGV was lower than mTGV for men (−0.49 ± 0.7 L; p < .0001). For men, %BF derived by pTGV was lower than that by mTGV (−1.3 ± 1.8%; p < .0001). For women, no differences were found between pTGV and mTGV (−0.08 ± 0.6 L; p > .05) or %BF (−0.03 ± 0.2%; p > .05). The two-predictor model of sex and height was able to account for 57.9% of the variance in mTGV, F(2, 178) = 122.5, p < .0001. Sex corrected for the effect of height was a significant predictor of mTGV (β = 0.483 L, p < .0001). There is bias for pTGV to underestimate mTGV in individuals with a large mTGV, which can lead to significant underestimations of %BF in young adults; this was especially evident for men in this study. Sex is an important covariate that should be considered when deciding to use pTGV. The results indicate that TGV should be measured whenever possible for both men and women ages 18–30 years.

The authors used 3-component (3C) Db-mineral-model (Lohman, 1986) reference measures to cross-validate Siri’s (1961) 2-component (2C) conversion formula and dual-energy X-ray absorptiometry (DXA) estimates of relative body fat (%BF) for physically active adults. Participants varied in age (18 to 59 y), body fatness, ethnicity (black, Hispanic, white), and physical activity level. The 3C Db-mineral model was used to obtain reference measures of %BF (%BF_3C) for comparison with body-composition measures from DXA and hydrodensitometry. For men (n = 110) and women (n = 110), %BF_3C (14.0% BF and 24.4% BF, respectively) was more accurately estimated by Siri’s 2C formula (%BF_Siri; men, r = 0.97, SEE = 1.77% BF; women, r = 0.98, SEE = 1.56% BF) than by DXA (%BF_DXA; men, r = 0.86, SEE = 3.54% BF; women, r = 0.88, SEE = 3.73% BF). The average %BF_Siri (men, 15.8% BF; women, 24.7% BF) and %BF_DXA (men, 16.2% BF; women, 26.0% BF) differed significantly (P < 0.001) from %BF_3C. Siri’s 2C model estimated the average %BF_3C in this sample more accurately than DXA did.

Reduced partial pressure of oxygen impairs exercise performance at altitude. Acute nitrate supplementation, at sea level, may reduce oxygen cost during submaximal exercise in hypobaric hypoxia. Therefore, we investigated the metabolic response during exercise at altitude following acute nitrate consumption. Ten well-trained (61.0 ± 7.4 ml/kg/min) males (age 28 ± 7 yr) completed 3 experimental trials (T1, T2, T3). T1 included baseline demographics, a maximal aerobic capacity test (VO_2max) and five submaximal intensity cycling determination bouts at an elevation of 1600 m. A 4-day dietary washout, minimizing consumption of nitrate-rich foods, preceded T2 and T3. In a randomized, double-blind, placebo-controlled, crossover fashion, subjects consumed either a nitrate-depleted beetroot juice (PL) or ~12.8 mmol nitrate rich (NR) beverage 2.5 hr before T2 and T3. Exercise at 3500 m (T2 and T3) via hypobaric hypoxia consisted of a 5-min warm-up (25% of normobaric (VO_2max) and four 5-min cycling bouts (40, 50, 60, 70% of normobaric VO_2max) each separated by a 4-min rest period. Cycling RPM and watts for each submaximal bout during T2 and T3 were determined during T1. Preexercise plasma nitrite was elevated following NR consumption compared with PL (1.4 ± 1.2 and 0.7 ± 0.3 uM respectively; p < .05). There was no difference in oxygen consumption (−0.5 ± 1.8, 0.1 ± 1.7, 0.7 ± 2.1, and 1.0 ± 3.0 ml/kg/min) at any intensity (40, 50, 60, 70% of VO_2max), respectively) between NR and PL. Further, respiratory exchange ratio, oxygen saturation, heart rate and rating of perceived exertion were not different at any submaximal intensity between NR and PL either. Blood lactate, however, was reduced following NR consumption compared with PL at 40 and 60% of VO_2max (p < .0.05). Our findings suggest that acute nitrate supplementation before exercise at 3500 m does not reduce oxygen cost but may reduce blood lactate accumulation at lower intensity workloads.