Deuterium oxide (D₂O) dilution is the criterion method for total body water (TBW) measurement, but results may vary depending on the specimen type, analysis method, and analyzing laboratory. Bioelectrical impedance (BIA) estimates TBW, but results may vary by device make and model. We investigated the accuracy and precision of TBW estimates and how measurement conditions affected the accuracy of body composition using multicompartment body composition models. Eighty collegiate athletes received duplicate TBW measures acquired from 3 BIA devices (S10, SFB7, and SOZO) and from unique D₂O combinations of specimen type (saliva, urine), analysis methodology [Fourier transform infrared spectrophotometry (FTIR), isotope-ratio mass spectrometry (IRMS)], and 3 different laboratories. TBW measures were substituted into 2-compartment (2C) and 5-compartment (5C) body composition models. Criterion measures were compared using Lin's concordance correlation coefficient cutoff of poor (0.99). Fifty-one participants (26 female) completed the protocol. Using IRMS saliva as the criterion TBW, all other measures produced a substantial or almost perfect agreement, except for SFB7 (poor) and SOZO (moderate). The 2C body composition measures using D₂O and BIA produced poor agreement except for moderate agreement for lab 3 FTIR saliva. The 5C body composition measures using D₂O produced a substantial agreement, whereas the BIA device S10 and SOZO had a moderate agreement, while the SFB7 had a poor agreement to the criterion. Test–retest precision varied between techniques from 0.3% to 1.2% for TBW. Small differences in TBW measurement led to significant differences in 2C models. The 5C models partially mitigate differences seen in 2C models when different TBW measures are used. Interchanging TBW measures in multicompartment models can be problematic and should be performed with these considerations.

Athletes vary in hydration status due to ongoing training regimes, diet demands, and extreme exertion. With water being one of the largest body composition compartments, its variation can cause misinterpretation of body composition assessments meant to monitor strength and training progress. In this study, we asked what accessible body composition approach could best quantify body composition in athletes with a variety of hydration levels. The Da Kine Study recruited collegiate and intramural athletes to undergo a variety of body composition assessments including air-displacement plethysmography (ADP), deuterium-oxide dilution (D₂O), dual-energy X-ray absorptiometry (DXA), underwater-weighing (UWW), 3D-optical (3DO) imaging, and bioelectrical impedance (BIA). Each of these methods generated 2- or 3-compartment body composition estimates of fat mass (FM) and fat-free mass (FFM) and was compared to equivalent measures of the criterion 6-compartment model (6CM) that accounts for variance in hydration. Body composition by each method was used to predict abdominal and thigh strength, assessed by isokinetic/isometric dynamometry. In total, 70 (35 female) athletes with a mean age of 21.8 ± 4.2 years were recruited. Percent hydration (Body Water_6CM/FFM_6CM) had substantial variation in both males (63-73 %) and females (58-78 %). ADP and DXA FM and FF M had moderate to substantial agreement with the 6C model (Lin's Concordance Coefficient [CCC] = 0.90-0.95) whereas the other measures had lesser agreement (CCC <0.90) with one exception of 3DO FFM in females (CCC = 0.91). All measures of FFM produced excellent precision with %CV < 1.0 %. However, FM measures in general had worse precision (% CV < 2.0 %). Increasing quartiles (significant p < 0.001 trend) of 6CM FFM resulted in increasing strength measures in males and females. Moreover, the stronger the agreement between the alternative methods to the 6CM, the more robust their correlation with strength, irrespective of hydration status. The criterion 6CM showed the best association to strength regardless of the hydration status of the athletes for both males and females. Simpler methods showed high precision for both FM and FFM and those with the strongest agreement to the 6CM had the highest strength associations. This study compared various body composition analysis methods in 70 athletes with varying states of hydration to the criterion 6-compartment model and assessed their relationship to muscle strength. The results showed that accurate and precise estimates of body composition can be determined in athletes, and a more accurate body composition measurement produces better strength estimates. The best laboratory-based techniques were air displacement plethysmography and dual-energy x-ray absorptiometry, while the commercial methods had moderate-poor agreement. Prioritizing accurate body composition assessment ensures better strength estimates in athletes.

Muscle mass and strength are crucial for physiological function and performance in athletes, playing a significant role in maintaining health and optimal athletic performance. Skeletal muscle, which constitutes the majority of lean soft tissue (LST) and appendicular lean soft tissue (ALST) when measured by dual-energy X-ray absorptiometry (DXA), represents a commonly used surrogate for strength. Research has investigated alternative measures of body composition, such as the assessment of ALST through bioelectrical impedance analysis (BIA) and the determination of whole-body muscle mass from creatine pool size using the deuterated creatine (D₃Cr) dilution method, for their associations to strength. While the relationship between body composition measures and strength has been studied in older adults, this relationship remains unexplored in athletic populations. This study examined muscle body composition measures using DXA, D₃Cr, and BIA and their association with strength in a sample of collegiate athletes. The study enrolled 80 collegiate athletes (40 females) of differing sports disciplines who consumed a 60 mg dose of D₃Cr and completed DXA and BIA measures in addition to trunk and leg strength tests. Analysis was sex-stratified using Pearson’s correlations, linear regression, and quartile p trend significance. With an average participant age of 21.8 years, whole-body DXA correlations to muscle strength surpassed height- or mass-normalized values. This trend was especially pronounced in trunk strength’s relationship with body composition over leg strength, across measurement methods. While DXA LST values were higher than BIA and D₃Cr in predicting strength, the values did not differ significantly. Adjustments for age, BMI, and BIA variables didn’t enhance this association. A significant trend between DXA LST and all strength measures underscored the equal relevance of DXA and D₃Cr muscle mass to strength, favoring whole-body over regional assessments. This calls for future research on muscle mass’s effects on LST and functional outcomes in broader groups, highlighting the importance of comprehensive body composition analysis in athletic performance studies.

Background: Measurements of body composition are helpful indicators of health outcomes, but muscle strength has a greater correlation with disease risk and long-term health outcomes, particularly among older adults. Whole-body DXA scans uniquely parse out total and regional lean soft tissue (LST) and appendicular (ALST), primarily composed of skeletal muscle and often used to diagnose sarcopenia and frailty. An alternative approach measures the enrichment of deuterated Creatinine (D ₃ Crn) in urine after ingesting a tracer dose of deuterated creatine (D ₃ Cr) to determine creatine pool size and estimate whole-body muscle mass. The utility of D ₃ Cr relationships between strength and body composition in young athletes has yet to be established. In this study, we investigated the association of muscle strength and body composition using multiple methods including DXA, D ₃ Cr, and bioelectrical impedance (BIA), in a collegiate athletic population. Methods: The Da Kine Study enrolled 80 multi-sport collegiate athletes. Each subject consumed a 60 mg dose of D ₃ Cr and completed whole-body DXA, BIA, and strength tests of the leg and trunk using an isokinetic dynamometer. The analysis was stratified by sex. Pearson’s correlations, forward stepwise linear regression and quartile p trend significance were used to show the associations of body composition measures to muscle strength. Results: The mean (SD) age of the 80 (40M/40F) athletes was 21.8 (4.2) years. Raw whole-body values had higher correlations with muscle strength in both sexes compared to the normalized values by height, body mass (BM), and BMI. DXA LST had the highest leg ( R ² =0.36, 0.37) and trunk ( R ² =0.53, 0.61) strength in both males and females. Trunk strength was more highly associated with body composition measures than leg strength in both sexes and all measurement techniques. One or more DXA LST measures (total, leg, and ALST) were consistently more highly associated with leg and trunk strengths for both sexes than BIA and D ₃ Cr measures. Adjusting all body composition values by age, BMI, and BIA variables did not improve the associations. A significant p trend across quartiles was observed for DXA LST and ALST for all measures of strength in both sexes. Conclusion: Although statistical significance was not reached between devices, DXA body composition output variables, especially LST, showed the highest associations with both sexes’ leg and trunk muscle strength. Furthermore, without adjustment for demographic information or BIA variables, whole-body values show stronger associations with muscle strength. Future research should investigate the impact of muscle mass changes on LST and functional measures.

Objective: To compare multiple body composition analysis methods in athletes with varying states of hydration to the criterion 5-compartment model(5CM) of body composition and assess the relationships of technique-specific estimates of fat and fat-free mass(FM, FFM) to muscle strength. Methods: Body composition was assessed in 80(40-female) athletes with a mean age of 21.8±4.2 years. All athletes underwent laboratory-based methods: air-displacement plethysmography(ADP), deuterium-oxide dilution(D ₂ O), dual-energy X-ray absorptiometry(DXA), underwater-weighing(UWW), and field-based: 3D-optical(3DO) imaging, and three bioelectrical impedance(BIA) devices(S10/SFB7/SOZO). Participants’ muscular strength was assessed by isokinetic/isometric dynamometry. Accuracy was assessed by Lin’s concordance correlation coefficient(CCC) and precision by root-mean-square coefficient of variation(RMS-CV%). Results: Athletes’ hydration status(total body water/FFM) was significantly( p <0.05) outside of the normal range in both males(0.63-0.73%) and females(0.58-0.78%). The most accurate techniques(ADP/DXA) showed moderate-substantial agreement(CCC=0.90-0.95) in FM and FFM, whereas all field assessments had poor agreement(CCC<0.90), except 3DO FFM in females(CCC=0.91). All measures of FFM produced excellent <1.0% precision, whereas FM from ADP, DXA, D ₂ O, S10, and UWW had <2.0%. The associations between muscle strength and the various devices’ FFM estimates differed. However, more accurate body composition compared to the criterion produced a better determination of muscle strength by significant quartile p -trends( p< 0.001). The 5CM exhibits the highest determination for all categories of muscle strength which persisted across all hydration measures. Conclusion: To optimize accuracy in assessing body composition and muscle strength, researchers and clinicians should prioritize selecting devices based on their accuracy compared to the 5CM. Reliable approaches such as ADP and DXA yield accurate and precise body composition estimates and thereby, better strength assessments, regardless of hydration status. Future athlete studies should investigate the impact of changes in FFM on functional measures compared to the criterion method. Summary Box: This study compared various body composition analysis methods in athletes with varying states of hydration to the criterion 5-compartment model(5CM) and assessed their relationship to muscle strength. The results showed that accurate and precise estimates of body composition can be determined in athletes, and a more accurate body composition measurement produced better strength estimates. The best laboratory-based techniques were air displacement plethysmography(ADP) and dual-energy x-ray absorptiometry(DXA), while field assessments had moderate-poor agreement. Prioritize accurate body composition assessment devices compared to the 5CM for better strength estimates in athletes.