Are Ethnic and Gender Specific Equations Needed to Derive Fat Free Mass from Bioelectrical Impedance in Children of South Asian, Black African-Caribbean and White European Origin? Results of the Assessment of Body Composition in Children Study

Background Bioelectrical impedance analysis (BIA) is a potentially valuable method for assessing lean mass and body fat levels in children from different ethnic groups. We examined the need for ethnic- and gender-specific equations for estimating fat free mass (FFM) from BIA in children from different ethnic groups and examined their effects on the assessment of ethnic differences in body fat. Methods Cross-sectional study of children aged 8–10 years in London Primary schools including 325 South Asians, 250 black African-Caribbeans and 289 white Europeans with measurements of height, weight and arm-leg impedance (Z; Bodystat 1500). Total body water was estimated from deuterium dilution and converted to FFM. Multilevel models were used to derive three types of equation {A: FFM = linear combination(height+weight+Z); B: FFM = linear combination(height2/Z); C: FFM = linear combination(height2/Z+weight)}. Results Ethnicity and gender were important predictors of FFM and improved model fit in all equations. The models of best fit were ethnicity and gender specific versions of equation A, followed by equation C; these provided accurate assessments of ethnic differences in FFM and FM. In contrast, the use of generic equations led to underestimation of both the negative South Asian-white European FFM difference and the positive black African-Caribbean-white European FFM difference (by 0.53 kg and by 0.73 kg respectively for equation A). The use of generic equations underestimated the positive South Asian-white European difference in fat mass (FM) and overestimated the positive black African-Caribbean-white European difference in FM (by 4.7% and 10.1% respectively for equation A). Consistent results were observed when the equations were applied to a large external data set. Conclusions Ethnic- and gender-specific equations for predicting FFM from BIA provide better estimates of ethnic differences in FFM and FM in children, while generic equations can misrepresent these ethnic differences

Salivary cortisol differs with age and sex and shows inverse associations with WHR in Swedish women: a cross-sectional study

<p>Abstract</p> <p>Background</p> <p>Most studies on cortisol have focused on smaller, selected samples. We therefore aimed to sex-specifically study the diurnal cortisol pattern and explore its association with abdominal obesity in a large unselected population.</p> <p>Methods</p> <p>In 2001–2004, 1811 men and women (30–75 years) were randomly selected from the Vara population, south-western Sweden (81% participation rate). Of these, 1671 subjects with full information on basal morning and evening salivary cortisol and anthropometric measurements were included in this cross-sectional study. Differences between groups were examined by general linear model and by logistic and linear regression analyses.</p> <p>Results</p> <p>Morning and Δ-cortisol (morning – evening cortisol) were significantly higher in women than men. In both genders older age was significantly associated with higher levels of all cortisol measures, however, most consistently with evening cortisol. In women only, age-adjusted means of WHR were significantly lower in the highest compared to the lowest quartile of morning cortisol (p = 0.036) and Δ-cortisol (p < 0.001), respectively. Furthermore, when comparing WHR above and below the mean, the age-adjusted OR in women for the lowest quartile of cortisol compared to the highest was 1.5 (1.0–2.2, p = 0.058) for morning cortisol and 1.9 (1.3–2.8) for Δ-cortisol. All findings for Δ-cortisol remained after adjustments for multiple covariates and were also seen in a linear regression analysis (p = 0.003).</p> <p>Conclusion</p> <p>In summary, our findings of generally higher cortisol levels in women than men of all ages are novel and the stronger results seen for Δ-cortisol as opposed to morning cortisol in the association with WHR emphasise the need of studying cortisol variation intra-individually. To our knowledge, the associations in this study have never before been investigated in such a large population sample of both men and women. Our results therefore offer important knowledge on the descriptive characteristics of cortisol in relation to age and gender, and on the impact that associations previously seen between cortisol and abdominal obesity in smaller, selected samples have on a population level.</p

The Role of Body Mass Index, Insulin, and Adiponectin in the Relation Between Fat Distribution and Bone Mineral Density

Despite the positive association between body mass index (BMI) and bone mineral density (BMD) and content (BMC), the role of fat distribution in BMD/BMC remains unclear. We examined relationships between BMD/BMC and various measurements of fat distribution and studied the role of BMI, insulin, and adiponectin in these relations. Using a cross-sectional investigation of 2631 participants from the Erasmus Rucphen Family study, we studied associations between BMD (using dual-energy X-ray absorptiometry (DXA]) at the hip, lumbar spine, total body (BMD and BMC), and fat distribution by the waist-to-hip ratio (WHR), waist-to-thigh ratio (WTR), and DXA-based trunk-to-leg fat ratio and android-to-gynoid fat ratio. Analyses were stratified by gender and median age (48.0 years in women and 49.2 years in men) and were performed with and without adjustment for BMI, fasting insulin, and adiponectin. Using linear regression (adjusting for age, height, smoking, and use of alcohol), most relationships between fat distribution and BMD and BMC were positive, except for WTR. After BMI adjustment, most correlations were negative except for trunk-to-leg fat ratio in both genders. No consistent influence of age or menopausal status was found. Insulin and adiponectin levels did not explain either positive or negative associations. In conclusion, positive associations between android fat distribution and BMD/BMC are explained by higher BMI but not by higher insulin and/or lower adiponectin levels. Inverse associations after adjustment for BMI suggest that android fat deposition as measured by the WHR, WTR, and DXA-based android-to-gynoid fat ratio is not beneficial and possibly even deleterious for bone

RESPONSES TO HANDGRIP HOLDS TO FAILURE AT TWO UNIQUE FATIGUE THRESHOLDS IN MEN AND WOMEN

Minyoung Kwak, Pasquale J. Succi, Brian Benitez, Jody L. Clasey, FACSM, Haley C. Bergstrom. University of Kentucky, Lexington, KY. BACKGROUND: Critical force (CF) reflects the highest force that can be maintained for a very long time without fatigue. Physical working capacity at the rating of perceived exertion (PWCRPE) is the highest force output that can be maintained for a very long time without an increase in RPE. This study compared the force, time to exhaustion (Tlim), and muscle oxygen saturation responses (SmO2) of men and women during continuous, isometric, handgrip holds to failure (HTF) at two fatigue thresholds, CF and PWCRPE. METHODS: The CF and PWCRPE were estimated for 10 men (Mean ± SD: Age 24.8 ± 4.1 yrs) and 10 women (Age 26.5 ± 3.5 yrs) from handgrip HTF at 4 different submaximal intensities (% maximum voluntary isometric contraction [MVIC]) force. CF (kg) was the slope coefficient of the total work (Wlim) for the 4 holds plotted as a function of Tlim. RPE was recorded every 10s during the 4 holds. PWCRPE (kg) was the y-intercept of the slope coefficients for the RPE vs. time relationships plotted as a function of force. During CF and PWCRPE HTF, Tlim was recorded and SmO2 responses were measured from the flexor digitorum superficialis with near-infrared spectroscopy. Analyses included 2-way mixed model ANOVAs and polynomial regression (p\u3c0.05). RESULTS: For absolute force, there was a main effect (p= 0.027) for sex (collapsed across threshold: Men 7.3 ± 2.8kg, Women 5.5 ± 1.8kg). There were no sex x threshold interactions (p=0.531-0.747) or main effects for relative force (collapsed across sex and threshold, %MVIC= 18.9 ± 6.4%) or Tlim (collapsed across sex and threshold, Tlim= 685.6 ± 386.0s). There were negative, quadratic relationships between SmO2 and time for CF (R2=0.852, p=0.013, SmO2Δ= -6.7 ± 17.1%) and PWCRPE (R2=0.910, p\u3c0.001, SmO2Δ= -5.8 ± 16.6%) for the men, and a negative, cubic response for PWCRPE for the women (R2=0.885, p=0.016, SmO2Δ= -0.7 ± 10.9%). However, there was no relationship between SmO2 and time for CF for women (r2=0.076, p\u3e0.05, SmO2Δ= -0.5 ± 8.6). CONCLUSIONS: The lack of differences in relative force or in the sustainability (Tlim) of CF and PWCRPE indicated that these thresholds reflect a similar intensity for the men and women. Interestingly, the negative, quadratic patterns of responses for SmO2 at CF and PWCRPE for the men, but no change at CF and a small (\u3c1%) decrease in SmO2 at the PWCRPE for the women, suggested that men may desaturate more during a fatiguing handgrip task

HEALTHY AND OBESE CLASSIFICATIONS: INFLUENCE ON CONSTANT LOAD TREADMILL BOUTS RESULTS

Mariana V. Jacobs, Trey R. Naylor, Justin Pol, Michael Samaan, Jody L. Clasey, FACSM. University of Kentucky, Lexington, KY. BACKGROUND: It has been previously reported that obese individuals have greater absolute and lower relative oxygen consumption measures compared to their healthy-weight counterparts during constant load exercise. However, the method of determining obesity status may significantly influence the results and conclusions of group comparisons. The purpose of this study was to compare the influence of classification methodology by using body mass index (BMI kg • m-2) and body fat percentage (%Fat) to assess oxygen consumption rates (VO2) during submaximal, constant load exercise. METHODS: Seventeen participants (F:8, Age 23.4 ± 2.7yrs) completed a 30-minute walking task on a treadmill at a constant self-selected speed while wearing a portable metabolic system to measure relative VO2 (mL• kg-1 • min-1). All participants underwent a total body DXA scan to assess %Fat. Participants were categorized as healthy (H) or obese (O) using two methods: 1) %Fat (World Health Organization; WHO) and 2) BMI. WHO guidelines indicate healthy %fat for females and males as 21-32% and 8-19%, respectively, with obese classified as those that exceed these sex specific ranges. A BMI of \u3c30 kg • m-2 and \u3e30 kg • m-2 were used to categorize participants as healthy and obese, respectively. Unpaired t-tests (p\u3c0.05) were used to assess between group differences as a function of categorization (WHO vs. BMI). Dependent variables included: walking speed (m • s-1), VO2 at the start (T0), end (T30), the change of VO2 (ΔVΟ2; T30-T0) and total VO2. RESULTS: When using BMI as classification criteria (H:11, O:6), obese participants had significantly lower VO2 at T0 (p\u3c0.01) and T30 (p=0.01), leading to a significantly lower total VO2 (p=0.01). Additionally, the obese participants walked at a 17.5% slower speed (p=0.04). When classified using the %Fat (H:8, O:9), healthy and obese participants walked at similar speeds (p=0.20) yet the obese group displayed trends of lower VO2 at T0 (p=0.07) and T30 (p=0.07) as well trends of lower total V02 (p=0.07). The ΔVΟ2 was similar between groups regardless of using the %Fat (p=0.44) or BMI (p=0.42) criterion. CONCLUSION: These results concur with previous results that in obese individuals, relative VO2 is lower when compared to healthy weight individuals during constant load exercise, despite criterion used. Future research will explore additional ways to classify participants for group comparative purposes

A PRELIMINARY ANALYSIS OF RESPONSES TO EXERCISE ANCHORED TO VIGOROUS INTENSITY HEART RATES

Djadmann Gustave, Pasquale J. Succi, Brian Benitez, Minyoung Kwak, Jody L. Clasey, FACSM, Kathryn R. Lanphere, Haley C. Bergstrom. University of Kentucky, Lexington, KY. BACKGROUND: Exercise prescription to improve cardiorespiratory endurance (CE) is often based on percentages of the reserve or maximum heart rate (HRmax). However, no studies have examined the responses to constant HR exercise at the current vigorous intensity recommendations. This study examined the responses to constant HR exercise at the upper (95%HRmax) and lower (77%HRmax) vigorous intensity range and quantified the time spent in the severe (\u3erespiratory compensation point [RCP]), heavy (ventilatory threshold [VT]), and moderate (METHODS: Six subjects (mean±SD age=26.4±4.8yrs, height=170.9±8.9cm, weight=73.5±11.3kg) performed a graded exercise test on a cycle ergometer to determine the maximum volume of oxygen consumption (V̇O2max),HRmax, 77% and 95% HRmax, peak power output (PPO), VT, and RCP. On separate days, subjects performed constant HR trials to exhaustion (or to 60 min, plus the time to reach the HR) at 77% (time to exhaustion [TLim]=51.06±19.12 min, range=25.33-64.67min) and 95% HRmax (TLim=21.17± 11.65min, range =8.00-35.67min) with V̇O2 and power output (P) recorded and normalized to their respective values at PPO in 10% intervals of TLim. Polynomial regression analyses were used to examine the change (positive, negative) and pattern (linear, quadratic) of V̇O2 and P (alpha=0.05). RESULTS: For each subject, the average HR at 77% (144±4 beats·min-1 [b·min-1]) and 95% (177±5 b·min-1) HRmax was maintained within a ±2 b·min-1 for each trial. At 77% HRmax, subjects demonstrated linear (n=2) and quadratic (n=4) decreases in V̇O2 and linear (n=3) and quadratic decreases in P (n=3). Subjects spent an average of 44.71±20.32, 6.33±9.12, and 0.00±0.00 min in the moderate, heavy, and severe intensity domains, respectively. At 95%HRmax, subjects demonstrated linear (n=5) and quadratic (n=1) decreases in V̇O2 and linear (n=4) and quadratic (n=2) decreases in P. Subjects spent an average of 8.06±9.97, 10.22±6.15, and 2.89±2.04 minutes in the moderate, heavy, and severe intensity domains, respectively. CONCLUSIONS: There were decreases in the metabolic cost of exercise that tracked P for exercise anchored to the lower and upper HR. The lower HR may be at an intensity that is too low to maximize the metabolic stimulus (exercise primarily in the moderate domain), while the upper HR may be at an intensity too high to be sustained for the recommended time (20-60min) to improve CE

PHYSIOLOGICAL, PERCEPTUAL, AND NEUROMUSCULAR RESPONSES TO VO2-CLAMP CYCLE ERGOMETRY EXERCISE

Pasquale J. Succi1, Taylor K. Dinyer-McNeely2, Caleb C. Voskuil3, Brian Benitez1, Minyoung Kwak1, Mark G. Abel1, Jody L. Clasey, FACSM1, Haley C. Bergstrom1. 1University of Kentucky, Lexington, KY. 2Oklahoma State University, Stillwater, OK. 3Texas Christian University, Fort Worth, TX. BACKGROUND: Recommendations for endurance exercise prescription are based on percentages of an individual’s heart rate (HR) or volume of oxygen consumption (V̇O2) maximum or reserve. These intensities are then extrapolated to a power output (P) or velocity. Previous work has demonstrated a dissociation of the physiological, perceptual, and neuromuscular responses to exercise anchored to the critical heart rate (CHR) compared to the P associated with CHR (PCHR). However, it is unclear if a similar dissociation, due to reductions in P to maintain the designated intensity, would be present during exercise anchored to the V̇O2 associated with CHR (V̇O2CHR). The purpose of this study was to examine the patterns in physiological (V̇O2, HR, P, respiration rate [RR], muscle oxygen saturation [%SmO2]), neuromuscular (electromyographic and mechanomyographic amplitude [EMG AMP, MMG AMP] and mean power frequency [EMG MPF, MMG MPF]), and perceptual (rating of perceived exertion [RPE]) responses during exercise at V̇O2CHR (V̇O2-clamp). METHODS: On separate days, ten participants (Age=25±4yrs;Height=173.1±11.9cm;Mass=74.7±8.5kg) performed a graded exercise test, 4 constant P trials at 85-100% of peak P (PP) to derive CHR and V̇O2CHR from the total heartbeats vs. time to exhaustion (TLim) and the V̇O2 vs. HR relationships, respectively. Responses were recorded during a trial to exhaustion at V̇O2CHR (32.86±7.12mL·kg-1·min-1; TLim=31.31±21.37min) and normalized in 10% intervals of TLim to their respective values at PP. RESULTS: The one-way repeated-measures ANOVA with follow-up Student Newman-Keuls tests indicated there were differences (p\u3c0.001) among timepoints for HR (mean±SD %change=8±3%), RR (43±38%), P (-15±5%), EMG MPF (10±8%), and RPE (65±38%), but no differences (p=0.077-0.955) for %SmO2 (-17±53%), EMG AMP (-3±16%), MMG AMP (40±61%), and MMG MPF (1±7%). CONCLUSIONS: The loss in performance observed during V̇O2-clamp exercise may provide a quantification of the inefficiency associated with the V̇O2 slow component phenomenon. The EMG, MMG, and %SmO2 responses suggested continued muscle activation levels despite the reductions in P, but the HR, RR, and RPE responses suggested a combination of feedforward and feedback mechanisms regulating TLim. V̇O2-clamp exercise may present a novel methodology to examine mechanisms of fatigue and future studies should examine responses to V̇O2-clamp exercise at a uniform threshold

COMPARISON OF RESPONSE TO EXERCISE AT CONSTANT HEART RATE VERSUS CONSTANT POWER OUTPUT

Pasquale J. Succi1, Taylor K. Dinyer-McNeely2, Caleb C. Voskuil3, Brian Benitez1, Minyoung Kwak1, Mark G. Abel1, Jody L. Clasey, FACSM1, Haley C. Bergstrom1. 1University of Kentucky, Lexington, KY. 2Oklahoma State University, Stillwater, OK. 3Texas Christian University, Fort Worth, TX. BACKGROUND: The current recommendations for improving cardiorespiratory endurance (CE) are based on percentages of VO2 or heart rate (HR) maximum or reserve. However, these intensities are often based on estimation equations that are extrapolated to power outputs (P) or velocities. The recent application of the critical power model to a physiological parameter in HR provides an individualized threshold which has demonstrated a dissociation of typical responses that have previously been described during constant P exercise. Therefore, the purpose of this study was to examine the patterns in physiological (VO2, HR, P, respiration rate [RR], muscle oxygen saturation [%SmO2]), neuromuscular (electromyographic and mechanomyographic amplitude [EMG AMP,MMG AMP] and mean power frequency [EMG MPF,MMG MPF]), and perceptual (rating of perceived exertion [RPE]) responses during exercise anchored at critical heart rate (CHR) versus the P associated with CHR (PCHR). METHODS: On separate days, nine participants (Age 26±3y) performed a graded exercise test (GXT), 4 constant P trials at 85%-100% of peak power output (PP) to derive CHR and PCHR from the total heartbeats vs time to exhaustion (Tlim) and P vs HR relationships, respectively. The physiological, neuromuscular, and perceptual responses were recorded during trials at CHR (173±9b·min-1,TLim=45.5±20.2min) and PCHR (198±58W,TLim=21.0±17.8min) and normalized in 10% intervals to their respective values at PP. RESULTS: There were significant mode (CHRvsPCHR) x normalized time (10%-100%TLim) interactions for all variables (p=0.00-0.036) except MMG AMP (p\u3e0.05). Follow-up one-way ANOVAs and Student Newman-Keuls tests indicated differences among the time points for CHR VO2 (mean±SD %change=-19±12%), PCHR VO2 (25±10%), PCHR HR (23±6%), CHR RR (24±23%), PCHR RR (105±53%), CHR P (-33±11%), CHR RPE (22±14%), PCHR RPE (65±26%), CHR %SmO2 (41±33%), PCHR %SmO2(-7±30%), CHR EMG AMP (-13±15%), PCHR EMG AMP (18±21%), CHR EMG MPF (9±8%), CHR MMG MPF (7±11%), and PCHR MMG MPF (1±11%). CONCLUSIONS: Exercise at CHR was more sustainable than exercise at PCHR due to decreases in P required to maintain HR. As a result, participants demonstrated a dissociation of the predictable responses seen in constant P exercise. These differences at CHR may indicate that exercise anchored by a physiological parameter provides a more sustainable exercise modality that can be used to improve CE