Body Volume Estimates Research Articles

Computer vision‐assisted photogrammetry and one‐image 3D modeling in marine mammals

AbstractImage processing using traditional photogrammetric methods is a labor‐intensive process. The collection of photogrammetry images during aerial surveys is expanding rapidly, creating new challenges to analyze images promptly and efficiently, while reducing human error during processing. Computer vision‐assisted photogrammetry, a field of artificial intelligence (AI), can automate image processing, greatly enhancing the efficiency of photogrammetry. Here, we present a practical and efficient program capable of automatically extracting the fine‐scale photogrammetry of East Asian finless porpoises (Neophocaena asiaeorientalis sunameri). Our results indicated that computer vision‐assisted photogrammetry could achieve the same accuracy as traditional photogrammetry, and the results of the comparisons were validated against the direct measurements. Three‐dimensional (3D) models using computer vision‐assisted photogrammetric morphometrics generated trustworthy body volume estimates. We also explored the one image‐based 3D modeling technique, which is less accurate, but still useful when only one image of the animal is available. Although several limitations exist in the current program, improvements could be made to narrow the virtual‐reality gap when more images are available for machine learning and training. We recommend this program for analyzing images of marine mammals possessing a similar morphological contour.

Smartphone derived anthropometrics: Agreement between a commercially available smartphone application and its parent application intended for use at point-of-care

Smartphone applications can now automate body composition and anthropometric measurements remotely, prompting applications intended for use at point-of-care to provide commercially available smartphone applications intended for personal use. However, the agreement between such anthropometrics remain unclear. A total of 123 apparently healthy participants (F: 69; M: 54; age: 28.1±11.3; BMI: 26.9±5.9) completed consecutive body composition scans using a 3D smartphone application intended for personal use (MeThreeSixty; MTS) and it stationary counterpart intended for use in practice (Mobile Fit Booth; MFB). Agreement between devices were evaluated using root mean square error (RMSE), Bland-Altman analyses, and linear regression for all measurements, and additional equivalence testing was conducted for all circumference and limb length comparisons. When evaluated against the MFB, MTS significantly overestimated all measurements other than waist circumference (p=0.670) using paired t-tests. RMSE was 2.5% for body fat percentage (BF%), 0.64-3.74cm for all body circumferences, 0.71-2.3kg for all lean mass estimates, and 126-659cm2 and 608-4672cm3 across all body surface area and body volume estimates, respectively. BF% was the only body composition estimate that did not demonstrate proportional bias (p=0.221). Circumferences of the chest, shoulder, biceps, forearm, and ankle all demonstrated proportional bias (all coefficients: p<0.050), but only chest, shoulder, and arm circumferences did not demonstrate equivalence. Arm surface area (p<0.001) and arm (p=0.002) and leg volumes (p=0.004) were the only body surface area and volume estimates to reveal proportional biases. These findings demonstrate the agreement between 3D anthropometric applications intended for clinical and personal use, particularly for whole-body composition estimates and clinically meaningful body circumferences. Given the advantages of commercially available remote applications, practitioners and consumers may consider using this method in place of those intended for clinical practice, but should express caution when overestimation is a concern.

Marine mammal morphometrics: 3D modeling and estimation validation

Techniques of 3D modeling have earned increasing popularity in scientific studies as they offered unprecedented traits in representing objects. As with all mathematical models, the 3D model will be useful once its accuracy has been validated with direct measurements and the robustness of its predictive capability tested. Although measures of body mass and volume are essential to comprehend the life history of animals, such morphometrics, especially total volume, are challenging to obtain from marine mammals due to their elusive nature, aquatic lifestyle, and large size. In this study, accurate measurements of body volume were directly detected from fresh carcasses of eleven finless porpoises (Neophocaena asiaeorientalis sunameri) and used to validate 3D models recreated from the same animals using Blender 3D graphics. Published models using truncated cones or elliptical shapes, based on 3, 5, 8, or 19 measurements of girths or heights &amp;amp; widths along the body, were also applied to porpoises to verify their accuracy. The Blender-generated 3D model produced the most accurate estimates of body volume compared to conventional truncated models, with a mean error of only 2.5% to the direct volume measurements. When photogrammetric images are available, the model can predict the body volumes based on total length alone. Similar accuracy was possible with the elliptical model using 19 height &amp;amp; width measurements (5% increments in total length). However, significant (p &amp;lt; 0.001) inaccuracy resulted from truncated models with 3, 5, or 8 girth measurements and elliptical models with 3 or 5 height &amp;amp; width measurements, and the accuracy of these models also decreased significantly as the number of measurement sites was reduced. Moreover, Blender 3D models can be extrapolated to animals with images absent, and such predicted volumes were tested to be trustworthy (overall skill = 0.998, r = 0.998, p &amp;lt; 0.01). Therefore, we recommend that researchers use either digital 3D models or elliptical models with 5% increments sectioning the torso to obtain accurate estimates of the body volumes of free-ranging marine mammals.

Agreement Between A 2-Dimensional Digital Image-Based 3-Compartment Body Composition Model and Dual Energy X-Ray Absorptiometry for The Estimation of Relative Adiposity

The purpose of this study was to compare relative adiposity (%Fat) derived from a 2-dimensional image-based 3-component (3C) model (%Fat3C-IMAGE) and dual-energy X-ray absorptiometry (DXA) (%FatDXA) against a 5-component (5C) laboratory criterion (%Fat5C). 57 participants were included (63.2% male, 84.2% White/Caucasian, 22.5±4.7 yrs., 23.9±2.8 kg/m2). For each participant, body mass and standing height were measured to the nearest 0.1 kg and 0.1 cm, respectively. A digital image of each participant was taken using a 9.7 inch, 16g iPad Air 2 and analyzed using a commercially available application (version 1.1.2, made Health and Fitness, USA) for the estimation of body volume (BV) and inclusion in %Fat3C-IMAGE . %Fat3C-IMAGE and %Fat5C included measures of total body water derived from bioimpedance spectroscopy. The criterion %Fat5C included BV estimates derived from underwater weighing and bone mineral content measures via DXA. %FatDXA estimates were calculated from a whole-body DXA scan. A standardized mean effect size (ES) assessed the magnitude of differences between models with values of 0.2, 0.5, and 0.8 for small, moderate, and large differences, respectively. Data are presented as mean ± standard deviation. A strong correlation (r = 0.94, p <.001) and small mean difference (ES = 0.24, p <.001) was observed between %Fat3C-IMAGE (19.20±5.80) and %Fat5C (17.69±6.20) whereas a strong correlation (r = 0.87, p <.001) and moderate-large mean difference (ES = 0.70, p <.001) was observed between %FatDXA (22.01±6.81) and %Fat5C. Furthermore, %Fat3C-IMAGE (SEE = 2.20 %Fat, TE= 2.6) exhibited smaller SEE and TE than %FatDXA (SEE = 3.14 %Fat, TE = 5.5). The 3C image-based model performed slightly better in our sample of young adults than the DXA 3C model. Thus, the 2D image analysis program provides an accurate and non-invasive estimate of %Fat within a 3C model in young adults. Compared to DXA, the 3C image-based model allows for a more cost-effective and portable method of body composition assessment, potentially increasing accessibility to multi-component methods.

Digital anthropometry via three-dimensional optical scanning: evaluation of four commercially available systems.

Digital anthropometry is increasingly accessible due to commercial availability of three-dimensional optical scanners (3DO). One hundred and seventy-nine participants were assessed by four 3DO systems (FIT3D®, Size Stream®, Styku®, and Naked Labs®) in duplicate, air displacement plethysmography (ADP), and dual-energy x-ray absorptiometry (DXA). Test-retest precision was evaluated, and validity of total and regional volumes was established. All scanners produced precise estimates, with root mean square coefficient of variation (RMS-%CV) of 1.1-1.3% when averaged across circumferences and 1.9-2.3% when averaged across volumes. Precision for circumferences generally decreased in the order of: hip, waist and thigh, chest, neck, and arms. Precision for volumes generally decreased in the order of: total body volume (BV), torso, legs, and arms. Total BV was significantly underestimated by Styku® (constant error [CE]: -10.1 L; root mean square error [RMSE]: 10.5 L) and overestimated by Size Stream® (CE: 8.0 L; RMSE: 8.3 L). Total BV did not differ between ADP and FIT3D® (CE: -3.9 L; RMSE: 4.2 L) or DXA BV equations (CE: 0-1.4 L; RMSE: 0.7-1.5 L). Torso volume was overestimated and leg and arm volumes were underestimated by all 3DO. No total or regional 3DO volume estimates exhibited equivalence with reference methods using 5% equivalence regions, and proportional bias of varying magnitudes was observed. All 3DO produced precise anthropometric estimates, although variability in specific precision estimates was observed. 3DO BV estimates did not exhibit equivalence with reference methods. Conversely, DXA-derived total BV exhibited superior validity and equivalence with ADP.

A novel method of utilizing skinfolds and bioimpedance for determining body fat percentage via a field-based three-compartment model.

The purpose was to determine if skinfolds (SF) and bioelectrical impedance analysis (BIA) could provide accurate estimates of body volume (BV) and total body water (TBW), respectively, for use in a 3-compartment (3-C) model to estimate percent body fat (BF%) when compared to laboratory derived measures. A sample of sixty-four men (age = 22.9 ± 5.4 years) and 59 women (age = 21.6 ± 4.3 years) participated in the study. Laboratory 3-C (3CLAB) model BF% was determined with underwater weighing for body volume (BV) and bioimpedance spectroscopy for total body water (TBW). The 3-C field (3CFIELD) estimates of BF% included BV from the 7-site SF technique and TBW from hand-to-foot BIA. A significant difference in BF% (p < 0.01) was found between the 3CLAB and 3CFIELD in the entire sample and within the men, but the effect sizes (ES) were small (0.09 and 0.17, respectively). The difference between means was not significant in the women (ES = 0.05, p = 0.332). Compared to the 3CLAB, the total error (TE) ranged 2.2-2.4% for 3CFIELD, 5.7-5.8% for SF, and 4.0-4.6% for BIA. The findings suggest that BV and TBW derived from SF and BIA, respectively, can be used in a 3CFIELD model to increase the accuracy of BF% estimates over SF and BIA alone.

Maternal body size and condition determine calf growth rates in southern right whales

The cost of reproduction is a key parameter determining a species' life history strategy. Despite exhibiting some of the fastest offspring growth rates among mammals, the cost of reproduction in baleen whales is largely unknown since standard field metabolic techniques cannot be applied. We quantified the cost of reproduction for southern right whales Eubalaena australis over a 3 mo breeding season. We did this by determining the relationship between calf growth rate and maternal rate of loss in energy reserves, using repeated measurements of body volume obtained from un manned aerial vehicle photogrammetry. We recorded 1118 body volume estimates from 40 female and calf pairs over 40 to 89 d. Calves grew at a rate of 3.2 cm d-1 (SD = 0.45) in body length and 0.081 m3 d-1 (SD = 0.011) in body volume, while females decreased in volume at a rate of 0.126 m3 d-1 (SD = 0.036). The average volume conversion efficiency from female to calf was 68% (SD = 16.91). Calf growth rate was positively related to the rate of loss in maternal body volume, suggesting that maternal volume loss is proportional to the energy investment into her calf. Maternal in vestment was determined by her body size and condition, with longer and more rotund females investing more volume into their calves compared to shorter and leaner females. Lactating females lost on average 25% of their initial body volume over the 3 mo breeding season. This study demonstrates the considerable energetic cost that females face during the lactation period, and highlights the importance of sufficientmaternal energyreserves for reproduction in this capital breeding species.

Allometric equations for estimating fresh biomass of five soil macroinvertebrate species from neotropical agroecosystems

Accurate estimation of soil macroinvertebrate fresh biomass is crucial to link macroinvertebrate community to ecosystem functions, but remains a challenging task under field conditions. Here, we present allometric equations to estimate the fresh biomass of three diplopods (Rhinocricidae), one earthworm (Glossoscolescidae) and one earwig species (Anisolabididae) that are abundant in soil communities and potentially important for the provision of soil ecological functions in tropical agroecosystems. Body length, body width, and body volume, were measured using a novel method of image analysis, and then used to estimate the fresh biomass. Our results show that length-biomass allometric relationships provide reliable estimation of fresh biomass for diplopods (r2 = 0.98) and earwigs (r2 = 0.97). However, the biomass of earthworms was not as accurately predicted by body length (r2 = 0.82). The use of body volume, estimated with body length and width, allowed to increase the predictive power for earthworms. Furthermore, a general allometric equation based on body volume, including all taxa considered in this study, was found to predict 96% of the observed body weight variability, suggesting that this equation could be generalizable to a large range of soil macroinvertebrates. Therefore, we conclude that using body volume could provide a better accuracy in estimating soil macroinvertebrate biomass. Although the estimation of body volume on each individual requires an additional measure, the use of image analysis software renders this step feasible for a large number of individuals. By improving the feasibility of trait measurements, this method may facilitate field surveys and foster trait-based studies on soil macroinvertebrates.

Reliability and agreement between DXA-derived body volumes and their usage in 4-compartment body composition models produced from DXA and BIA values

ABSTRACTTwo research groups recently produced equations for estimation of body volume from dual-energy x-ray absorptiometry (DXA) scans. These body volume estimates can be used for body composition evaluation in modified 4-compartment models. In the present analysis, the reliability of body volume calculations, as well as their usage in 4-compartment models, was explored while employing precise scheduling of assessments and dietary standardization. Forty-eight recreationally active males and females completed two pairs of identical assessments, which included a DXA scan and single-frequency bioelectrical impedance analysis. Each assessment within a pair was separated by 24 hours, during which participants were provided a standardized diet. Body volume and 4-compartment equations were applied to the data, and metrics of reliability and agreement were calculated for body volume and 4-compartment components. While both body volume equations demonstrated excellent reliability individually, substantial disagreement between equations was present when utilized in 4-compartment equations. The magnitude of this disagreement was 4.3 kg for lean mass and fat mass and 6.9% for body fat percentage. At present, the large discrepancies in body composition components when using existing body volume equations preclude their interchangeability and demonstrate the need for continued exploration of the utility of body volume estimates.

Evaluation of simple body composition methods: assessment of validity in prepubertal Chilean children.

The aim of this study was to assess the validity of body fatness estimations based on skinfolds and bioelectrical iImpedance analyses (BIA) measurements compared to a three-component model (3C model) in prepubertal Chilean children, considering potential differences by sex and nutritional status. Four hundred and twenty four Chilean children (198 females and 226 males) were assessed for body composition. Body fat percentage (BF%) was evaluated by Skinfold equations (Slaughter, Ramirez and Huang) and Bioelectrical impedance (BIA: Tanita BC-418MA) using both the equipment and the Ramirez equation. Measurements based on a 3C model constructed from total body water estimates by isotope dilution and from body volume estimates by air displacement plethysmography were used as gold standard. Coefficient of determination (R2) values were higher in overweight and in the whole group of both gender. All slopes were differed significantly from 1, and most intercepts were significantly different from 0. Skinfold Equations: an underestimation of BF% was found for all equations, being higher with the Slaughter equation. BIA: Tanita underestimated BF% in all groups, whereas Ramirez equation shows an overestimation. Skinfolds and bio-impedance equations serve well to rank children according to their BF%. However, these methods are not accurate for describing body composition in prepubertal Chilean children.

Desiccation Tolerance in the Tardigrade Richtersius coronifer Relies on Muscle Mediated Structural Reorganization

Life unfolds within a framework of constraining abiotic factors, yet some organisms are adapted to handle large fluctuations in physical and chemical parameters. Tardigrades are microscopic ecdysozoans well known for their ability to endure hostile conditions, such as complete desiccation – a phenomenon called anhydrobiosis. During dehydration, anhydrobiotic animals undergo a series of anatomical changes. Whether this reorganization is an essential regulated event mediated by active controlled processes, or merely a passive result of the dehydration process, has not been clearly determined. Here, we investigate parameters pivotal to the formation of the so-called "tun", a state that in tardigrades and rotifers marks the entrance into anhydrobiosis. Estimation of body volume in the eutardigrade Richtersius coronifer reveals an 87 % reduction in volume from the hydrated active state to the dehydrated tun state, underlining the structural stress associated with entering anhydrobiosis. Survival experiments with pharmacological inhibitors of mitochondrial energy production and muscle contractions show that i) mitochondrial energy production is a prerequisite for surviving desiccation, ii) uncoupling the mitochondria abolishes tun formation, and iii) inhibiting the musculature impairs the ability to form viable tuns. We moreover provide a comparative analysis of the structural changes involved in tun formation, using a combination of cytochemistry, confocal laser scanning microscopy and 3D reconstructions as well as scanning electron microscopy. Our data reveal that the musculature mediates a structural reorganization vital for anhydrobiotic survival, and furthermore that maintaining structural integrity is essential for resumption of life following rehydration.

Dwarfing of ostracodes during the Paleocene–Eocene Thermal Maximum at DSDP Site 401 (Bay of Biscay, North Atlantic) and its implication for changes in organic carbon cycle in deep-sea benthic ecosystem

The Paleocene–Eocene Thermal Maximum (PETM) has been held up as a past analog to future environmental change and presents the opportunity to study climate impacts on marine communities. During the PETM, deep-sea benthic foraminifers decreased their body-size and increased their productivity, metabolic rates, and food consumption in response to abruptly increasing temperature and changing surface water productivity. Here we find that three species of marine ostracodes – part of the multicellular benthos – also experienced a reduction in body-size in response to PETM warming in the Northeast Atlantic. Positive correlations between ostracode body-size and benthic foraminiferal oxygen isotope data indicate that reduced body-sizes were caused by high temperature during the PETM. Dwarfing of ostracodes during the PETM interval suggests that their food consumption rates, and lifetimes, were less than those of ostracodes in the pre-PETM interval. This interpretation is based upon previous studies that show that food consumption and ostracode lifetimes both decrease as ostracodes increase their growth rates under higher temperatures. Estimates of body volume, temperature, and individual abundance suggest a decline in lifetime metabolic rate in ostracode individuals during the core of the PETM. In addition there is also a decrease in biomass flux in the whole ostracode community at this time. The decline in biomass flux at the community level suggests major changes in the energy flow and carbon cycling in deep-sea benthic ecosystem and the reduction of organic carbon flux between the ostracode community and sediments during the PETM. The decline in ostracode carbon flux stands in contrast with previous interpretations that carbon cycling by benthic foraminifera increased during the PETM. Hence, our data suggest that the benthic community response to the PETM was not uniform between different taxonomic groups.

Evaluation of a Rotary Laser Body Scanner for Body Volume and Fat Assessment

This paper reports the evaluation tests on the reliability and validity of a 3-dimensional (3D) laser body scanner for estimation of body volume and % fat. Repeated measures of body imaging were performed for reproducibility analysis. Validity of the instrument was assessed by comparison of measures of body volume by imaging to hydrodensitometry, and body fat was compared to hydrodensitometry and dual energy X-ray absorptiometry. Reproducibility analysis showed little difference between within-subjects measurements of volume (ICC ≥ 0.99, p < 0.01). Body volume estimations by laser body scanner and hydrodensitometry were strongly related (r = 0.99, p < 0.01), and agreement was high (ICC = 0.99, p < 0.01). Measurements of % body fat also agreed strongly with each other between methods (ICC = 0.86, p < 0.01), and mean % fat estimates by body imaging did not differ from criterion methods (p > 0.05). These findings indicate that the 3D laser body scanner is a reliable and valid technique for the estimation of body volume. Furthermore, body imaging is an accurate measure of body fat, as compared to dual energy X-ray absorptiometry. This new instrument is promising as a quick, simple to use, and inexpensive method of body composition analysis.

Effect of different swim caps on the assessment of body volume and percentage body fat by air displacement plethysmography

Isothermal air trapped in scalp hair generates an underestimation of body volume when it is measured by air displacement plethysmography. The aim of this study was to examine the effect of wearing different types of swim caps on the measurement of body volume and percentage body fat by air displacement plethysmography. It was hypothesized that wearing a silicone swim cap would more thoroughly compress scalp hair compared with a lycra swim cap, yielding higher estimates of body volume and percent body fat. Thirty female participants aged 25.7 ± 6.4 years were measured in random order when wearing no swim cap, a lycra swim cap or a silicone swim cap. For the no-cap versus lycra cap condition, the mean bias for body volume was −0.579 ± 0.380 litre (limits of agreement: −1.340 to 0.181 litre) and for percent fat −4.9 ± 3.1% fat (limits of agreement: −11.2 to 1.3% fat) (P < 0.05). For the silicone versus lycra condition, the mean bias for body volume was 0.137 ± 0.099 litre (limits of agreement: −0.062 to 0.335 litre) and for percent fat 1.2 ± 0.9% fat (limits of agreement: −0.5 to 2.9% fat) (P < 0.05). In conclusion, attention should be paid to optimal compression of isothermal air trapped in scalp hair when using air displacement plethysmography. The present results suggest that this compression may be more thorough when wearing a silicone swim cap.

Using Simple Body-Size Metrics to Estimate Fossil Body Volume: Empirical Validation Using Diverse Paleozoic Invertebrates

Body size is one of the most significant organismal characteristics because of its strong association with nearly all important ecological and physiological characteristics. While direct body mass measurement (or estimation from other size metrics) is not feasible with most extinct taxa, body volume is a measurable and general proxy for fossil size. This study explores the reliability of several metrics that can be used to estimate the body volume of Paleozoic invertebrates of various sizes, shapes, taxonomic affinities, and ecological habits. The ATD model, based on the product of lengths of the three major body axes (anteroposterior, transverse, and dorsoventral), is simple and widely applicable. Models specific to particular morphological and taxonomic groups are slightly more accurate than this ATD model, but the advantages are minor. The ATD model is consistent with previous studies demonstrating widespread shape allometry—that is, small taxa tend to have globose geometries while large ones tend to be conical, even within the same taxonomic group. The ATD model successfully predicts the volume of 10 validation samples that were excluded from development of the original model. Because the linear measurements used to estimate volume are easy to obtain from specimens in the field or from published work, estimates of body volume can be incorporated into paleontological analyses, even those spanning multiple phyla.

Within- and between-laboratory precision in the measurement of body volume using air displacement plethysmography and its effect on body composition assessment

To determine and compare the extent of within- and between-laboratory precision in body volume (BV) measurements using air displacement plethysmography (ADP), the BOD POD body composition system, and to interpret any such variability in terms of body composition estimates. Repeated test procedures of BV assessment using the BOD POD ADP were reproduced at two laboratories for the estimation of precision, both within and between laboratories. In total, 30 healthy adult volunteers, 14 men (age, 19-48 y; body mass index (BMI), 19.7-30.3 kg/m2) and 16 women (age, 19-40 y; BMI, 16.3-35.7 kg/m2), were each subjected to two test procedures at both laboratories. Two additional volunteers were independently subjected to 10 repeated test procedures at both laboratories. Repeated measurements of BV, uncorrected for the effects of isothermal air in the lungs and the surface area artifact, were obtained using the BOD POD ADP, with the identical protocol being faithfully applied at both laboratories. Uncorrected BV measurements were adjusted to give estimates of actual BV that were used to calculate body density (body weight (BWt)/actual BV) from which estimates of body composition were derived. The differences between repeated BV measurements or body composition estimates were used to assess within-laboratory precision (repeatability), as standard deviation (SD) and coefficient of variation; the differences between measurements reproduced at each laboratory were used to determine between-laboratory precision (reproducibility), as bias and 95% limits of agreement (from SD of the differences between laboratories). The extent of within-laboratory methodological precision for BV (uncorrected and actual) was variable according to subject, sample group and laboratory conditions (range of SD, 0.04-0.13 l), and was mostly due to within-individual biological variability (typically 78-99%) rather than to technical imprecision. There was a significant (P<0.05) bias between laboratories for the 10 repeats on the two independent subjects (up to 0.29 l). Although no significant bias (P=0.077) was evident for the sample group of 30 volunteers (-0.05 l), the 95% limits of agreement were considerable (-0.68 to 0.58 l). The effects of this variability in BV on body composition were relatively greater: for example, within-laboratory precision (SD) for body fat as % BWt was between 0.56 and 1.34% depending on the subject and laboratory; the bias (-0.59%) was not significant between laboratories, but there were large 95% limits of agreement (-3.67 to 2.50%). Within-laboratory precision for each BOD POD instrument was reasonably good, but was variable according to the prevailing conditions. Although the bias between the two instruments was not significant for the BV measurements, implying that they can be used interchangeably for groups of similar subjects, the relatively large 95% limits of agreement indicate that greater consideration may be needed for assessing individuals with different ADP instruments. Therefore, use of a single ADP instrument is apparently preferable when assessing individuals on a longitudinal basis.

EFFECT OF A COLD SKIN AND WARM AIR TEMPERATURE DIFFERENCE ON ESTIMATION OF BODY VOLUME USING AN AIR-DISPLACEMENT PLETHYSMOGRAPH

Air-displacement plethysmographs (ADP) have been used to predict body density (BD) (mass/volume) by estimating body volume (BV). This estimate is made by measuring changes in air pressure and applying Boyle's Law (pressure-volume relationship). The final estimation of BV is corrected by adjusting for the influence of isothermic air found on the surface of the skin. To reduce the measurement error associated with having warmer than expected air on or near the skin, it is recommended that individuals refrain from exercise and be minimally clothed prior to testing with an ADP. It is not clear, however, how having cold skin temperatures, in a warm ADP environment, might affect BV estimates. PURPOSE To determine if a cold skin and warm air temperature difference affects estimation of BV using an ADP. METHODS Two estimates of BV were made using an ADP on 16 men and 16 women (23.1±2.4 yrs). The first was obtained while the skin was warmer (SW), 32.7854±1.4433°C. The subsequent while the skin was significantly (p < 0.01) cooler (SC), 29.4876±1.4568°C. Skin cooling was done by having the participant sit in front of fans in an air-conditioned, isolated, room (16.49±0.54°C) for 15 min. Means were compared using pair t-tests and Bonforoni corrections procedures. RESULTS Skin temperature was 1.8405±1.3954°C warmer and 1.0234±1.4759°C colder than the air in the ADP during SW and SC, respectively. BV estimates were significantly lower following SC (67.4019±16.8578 vs. 67.5597±16.8683L, p < 0.01). This resulted in a significantly higher estimation of BD (1.0455±0.0199 vs. 1.0437±0.0194kg/L, p < 0.01) and lower predicted percent body fat (23.6405±9.1540 vs. 24.4362±8.9179%, p < 0.01) after SC. CONCLUSION Cooler than expected skin, in comparison to ADP air temperature, resulted in a lower estimate of BV and under prediction of percent body fat. While the results are statistically significant, they are small and perhaps without practical significance. They do suggest that BV estimates using an ADP can be optimized if care is taken to assure the skin is not cold in comparison to the air in the ADP.

EFFECT OF SCALP AND FACIAL HAIR ON PERCENT BODY FAT ESTIMATES BY THE BOD POD

Objective To determine the effect of body hair (scalp and facial) on BOD POD estimates of percent body fat. Methods and Procedures Twenty-five males (31.4 ± 8.0 yr, 83.4 ± 12.2 kg, 181.8 ± 6.9 cm) agreed to grow a beard for three weeks in order to participate in the study. Total body density (g/cm3) and percent body fat were evaluated by air displacement plethysmography (BOD POD). To observe the effect of trapped isothermal air in body hair, BOD POD measures were performed in four conditions: Criterion method (the beard was shaven and a swimcap was worn), facial hair and swimcap, facial hair and no swimcap, and no facial hair and no swimcap. Results The presence of only a beard (facial hair and swimcap) resulted in a significant underestimation of percent fat (16.2%; 1.0618 g/cm3) vs. the Criterion method (17.1%; 1.0597 g/cm3; P < 0.001). The effect of scalp hair (no swim cap worn) resulted in a significant underestimation in percent fat relative to the Criterion method, either with facial hair (facial hair and no swimcap, 14.8%; 1.0649 g/cm3) or without facial hair (no facial hair and no swimcap, 14.8%; 1.0650 g/cm3; P < 0.001 for both). Discussion A significant underestimation of percent fat was observed with the presence of facial hair (∼1%) and scalp hair (∼2.3%). This underestimation in percent fat may be due to the effect of trapped isothermal air in body hair on body volume estimates. Thus, excess facial hair should be kept to a minimum and a swim cap worn at all times to ensure accurate estimates of body fat when using the BOD POD.

Effect of scalp and facial hair on air displacement plethysmography estimates of percentage of body fat.

The objective of this study was to determine the effect of body hair (scalp and facial) on air displacement plethysmography (BOD POD) estimates of percentage of body fat. A total of 25 men (31.4 +/- 8.0 years, 83.4 +/- 12.2 kg, 181.8 +/- 6.9 cm) agreed to grow a beard for 3 weeks to participate in the study. Total body density (g/cm(3)) and percentage of body fat were evaluated by BOD POD. To observe the effect of trapped isothermal air in body hair, BOD POD measures were performed in four conditions: criterion method (the beard was shaven and a swimcap was worn), facial hair and swimcap, facial hair and no swimcap, and no facial hair and no swimcap(.) The presence of only a beard (facial hair and swimcap) resulted in a significant underestimation of percentage of body fat (16.2%, 1.0618 g/cm(3)) vs. the criterion method (17.1%, 1.0597 g/cm(3), p < 0.001). The effect of scalp hair (no swim cap worn) resulted in a significant underestimation in percentage of body fat relative to the criterion method, either with facial hair (facial hair and no swimcap; 14.8%, 1.0649 g/cm(3)) or without facial hair (no facial hair and no swimcap; 14.8%, 1.0650 g/cm(3), p < 0.001 for both). A significant underestimation of percentage of body fat was observed with the presence of facial hair ( approximately 1%) and scalp hair ( approximately 2.3%). This underestimation in percentage of body fat may be caused by the effect of trapped isothermal air in body hair on body-volume estimates. Thus, excess facial hair should be kept to a minimum and a swimcap should be worn at all times to ensure accurate estimates of body fat when using the BOD POD.

THE MEASUREMENT OF BODY VOLUME IN PRETERM INFANTS BY ACOUSTIC PLETHYSMOGRAPHY

An accurate measurement of body volume is essential when body protein and fat are estimated by the densitometric method expanded to a four compartment system: total body water, protein, fat, and mineral. Total body fat and lean body mass comprise the usual two compartment system. The acoustic plethysmograph, based on the Helmholtz resonator principle, was tested with miniature pigs. Body volume was estimated with a reproducibility of 2.5% and no differences were noted between volumes estimated by that method and water displacement. That initial prototype was affected significantly by temperature; a 1° deviation at 35° C resulted in a 2.5% change in body volume estimates. A constant temperature chamber has been designed. The body volume of 8 preterm infants (postnatal age and body weight ranges were 2.5 - 11 wks and 1423 - 2425 g, respectively) was measured. Ten measurements, each of 1 min duration, were obtained on each subject. The mean coefficient of variation of the measurements was 1.43 ± 0.55%. Body volumes and densities ranged from 1382 - 2450 cc and 0.97 - 1.067 g/cc (mean = 1.028 ± 0.024 g/cc), respectively. The reproducibility also was tested from measurements obtained on the same infants on two consecutive days. The mean difference between measurements was 0.7 ± 0.6%. This method is rapid, noninvasive, has a low coefficient of variation, and is ideal to measure the body volumes of infants.