The current standard measure of cardiorespiratory fitness introduces confounding by body mass: the DR's EXTRA study

Distinct effects of type 2 diabetes and obesity on cardiopulmonary performance

AIM

Effort intolerance is frequent in patients with overweight/obesity and/or type 2 diabetes (T2D) free from cardiac and respiratory disease. We sought to quantify the independent effects of T2D and body mass index (BMI) on cardiopulmonary capacity and gain insights on the possible pathophysiology by case-control and regression analyses.

METHODS

Patients at high/moderate cardiovascular risk, with or without T2D, underwent spirometry and combined echocardiography-cardiopulmonary exercise test as part of their clinical workup. Subjects with evidence of cardiopulmonary disease were excluded. The effects of T2D and obesity were estimated by multivariable models accounting for known/potential confounders and the major pathophysiological determinants of oxygen uptake at peak exercise (VO2peak ) normalized for fat-free mass (FFM).

RESULTS

In total, 109 patients with T2D and 97 controls were included in the analysis. The two groups had similar demographic and anthropometric characteristics except for higher BMI in T2D (28.6 ± 4.6 vs. 26.3 ± 4.4 kg/m2 , p = .0003) but comparable FFM. Patients with T2D achieved lower VO2peak than controls (18.5 ± 4.4 vs. 21.7 ± 8.3 ml/min/kg, p = .0006). Subclinical cardiovascular dysfunctions were observed in T2D: concentric left ventricular remodelling, autonomic dysfunction, systolic dysfunction and reduced systolic reserve. After accounting for confounders and major determinants of VO2peakFFM , T2D still displayed reduced VO2peak by 1.0 (-1.7/-0.3) ml/min/kgFFM , p = .0089, while the effect of BMI [-0.2 (-0.3/0.1) ml/min/kgFFM , p = .06 per unit increase], was largely explained by a combination of chronotropic incompetence, reduced peripheral oxygen extraction, impaired systolic reserve and ventilatory (in)efficiency.

CONCLUSIONS

T2D is an independent negative determinant of VO2peak whose effect is additive to other pathophysiological determinants of oxygen uptake, including BMI.

Epicardial fat and Stage B heart failure among overweight/obese and normal weight individuals with diabetes mellitus

PURPOSE

Although up to 20% of people with type 2 diabetes (DM) have normal BMI (< 25 kg/m2), it remains unclear whether there is a difference in the development of cardiac dysfunction between those with normal and higher BMI. Furthermore, little is known about the relationship of visceral fat with BMI or fitness in asymptomatic patients with DM.

METHODS

We prospectively enrolled asymptomatic patients with DM and divided into two groups: BMI ≥ 25kg/m2 (overweight/obese group) versus < 25kg/m2(normal-weight group). Resting echocardiogram followed by exercise stress echocardiogram and exercise gas exchange analysis (in a subgroup) was performed. Cardiac function was evaluated using left ventricular longitudinal strain (LVLS), E/e', and relative wall thickness (RWT). In addition, epicardial fat thickness (EFT) was measured to estimate visceral fat.

RESULTS

Normal-weight patients with DM had more EFT compared with overweight/obese patients (0.66 ± 0.17 cm vs. 0.59 ± 0.22 cm, p < 0.05), despite the overlap between the groups. There was no significant difference in the prevalence of LV remodeling (p = 0.49), impaired LVLS (p = 0.22), or increased E/e' (p = 0.26), and these were consistently observed when matched for race. The majority of patients (63%) achieved ≥ 85% of percent peak-predicted VO2. At peak, there was no significant difference in peak VO2 normalized by eLBM (36.4 ± 7.7 vs. 37.8 ± 7.1 ml/kg eLBM/min, p = 0.43) while VO2 normalized by weight (23.6 ± 6.5 vs. 29.6 ± 6.7 ml/kg/min, p < 0.001) and VO2 ratio (5.7 ± 1.7 vs. 7.3 ± 2.4 METs, p = 0.001) were significantly lower in patients with obese/overweight group. There was no significant difference between patients with higher and lower EFT.

CONCLUSIONS

Patients with DM and normal BMI have excess epicardial fat compared to those with overweight/obese. Epicardial fat was not directly linked to prevalence of subclinical dysfunction.

Clinical and invasively-measured predictors of high exercise capacity in Fontan patients

INTRODUCTION

Fontan patients have variable exercise capacity. Contemporary understanding as to which factors predict high tolerance is limited.

METHODS

Records from the Ahmanson/University of California, Los Angeles Adult Congenital Heart Disease Center were reviewed for adult Fontan patients who underwent CPET. Patients were considered "high performers" if their maximum oxygen uptake (VO2 max/kg)-predicted was greater than 80%. Cross-sectional clinical, hemodynamic, and liver biopsy data was gathered. High-performers were compared to control patients across these parameters via associations and regression.

RESULTS

A total of 195 adult patients were included; 27 patients were considered "high performers". They had lower body mass indices (BMI, p < 0.001), mean Fontan pressures (p = 0.026), and cardiac outputs (p = 0.013). High performers also had higher activity levels (p < 0.001), serum albumin levels (p = 0.003), non-invasive and invasive systemic arterial oxygen saturations (p < 0.001 and p = 0.004), lower New York Heart Association (NYHA) heart failure class (p = 0.002), and were younger at Fontan completion (p = 0.011). High performers had less severe liver fibrosis (p = 0.015). Simple regression found Fontan pressure, non-invasive O2 saturation, albumin level, activity level, age at Fontan surgery, NYHA class, and BMI to predict significant changes in VO2 max/kg %-predicted. These associations persisted in multiple regression for non-invasive O2 saturation, NYHA class II, activity level, and BMI.

CONCLUSIONS

Thin Fontan patients who exercise more had better exercise capacity, Fontan hemodynamic profiles, and less liver fibrosis.

25-Hydroxyvitamin D and Cardiorespiratory Fitness in Prepubertal Overweight and Obese Children

Childhood obesity has become a major global health problem. Vitamin D deficiency and poor cardiorespiratory fitness are highly prevalent in children with overweight or obesity, but little is known about their relationships. In this study, we aimed to analyze the relationship between serum 25-hydroxyvitamin D (25(OH)D) and cardiorespiratory fitness parameters in prepubertal obese and overweight children. A cross-sectional design with a sample of 57 prepubertal children, aged 9–11 years, with overweight or obesity was used. The fasting concentration of 25(OH)D was analyzed with a chemiluminescent microparticle immunoassay. Fat and lean body masses were determined by using DXA. Maximal oxygen uptake (VO_2max) was measured with the maximal treadmill test. A total of 68.4% of the sample had sufficient levels of 25(OH)D. As expected, their cardiorespiratory fitness was poor compared with that of normal-weight children, but 60% of the group exceeded the median obesity-specific reference values. No differences were found between the sexes for relative VO_2max or 25(OH)D levels. Moreover, no correlations were found between 25(OH)D and body composition or cardiorespiratory parameters for sex or vitamin D groups. Vitamin D status seems not to be directly related to body composition or cardiorespiratory fitness in prepubertal overweight or obese children.

Fitness, Fatness, and Mortality in Men and Women From the UK Biobank: Prospective Cohort Study

Background Cardiorespiratory fitness may moderate the association between obesity and all-cause mortality (ie, the "fat-but-fit" hypothesis), but unaddressed sources of bias are a concern. Methods and Results Cardiorespiratory fitness was estimated as watts per kilogram from a submaximal bicycle test in 77 169 men and women from the UK Biobank cohort and combined with World Health Organization standard body mass index categories, yielding 9 unique fitness-fatness combinations. We also formed fitness-fatness combinations based on bioimpedance as a direct measure of body composition. All-cause mortality was ascertained from death registries. Multivariable-adjusted Cox regression models were used to estimate hazard ratios and 95% CIs. We examined the association between fitness-fatness combinations and all-cause mortality in models with progressively more conservative approaches for accounting for reverse causation, misclassification of body composition, and confounding. Over a median follow-up of 7.7 years, 1731 participants died. In our base model, unfit men and women had higher risk of premature mortality irrespective of levels of adiposity, compared with the normal weight-fit reference. This pattern was attenuated but maintained with more conservative approaches in men, but not in women. In analysis stratified by sex and excluding individuals with prevalent major chronic disease and short follow-up and using direct measures of body composition, mortality risk was 1.78 (95% CI, 1.17-2.71) times higher in unfit-obese men but not higher in obese-fit men (0.94 [95% CI, 0.60-1.48]). In contrast, there was no increased risk in obese-unfit women (1.09 [95% CI, 0.44-1.05]) as compared with the reference. Conclusions Cardiorespiratory fitness modified the association between obesity and mortality in men, but this pattern appeared susceptible to biases in women.

Factors independently associated with cardiorespiratory fitness in patients with non-alcoholic fatty liver disease

Low cardiorespiratory fitness (CRF) is associated with non-alcoholic fatty liver disease (NAFLD) and low CRF is an important risk factor for cardiovascular disease. The factors that influence CRF in NAFLD are poorly understood and it has been suggested that reduced hepatic mitochondrial function (HMF) may be linked to low CRF. Therefore, our aim was to determine the factors associated with CRF in NAFLD.

METHODS

Ninety-seven patients with NAFLD were studied. CRF was assessed by treadmill testing and expressed as maximal O₂ consumption (VO₂ peak) per lean body mass. HMF was assessed by the ¹³ C-ketoisocaproate breath test. Multivariable linear regression modelling was undertaken to test the independence of associations with CRF.

RESULTS

Mean (SD) age was 51 (13) years and 61% were men. With CRF as the outcome, age (B coefficient -0.3, 95%CI -0.4, -0.2, P < .0001), total body fat mass (B coefficient -0.2, 95%CI -0.3, -0.05, P = .01), type 2 diabetes mellitus (T2DM) (B coefficient -3.6, 95%CI -1.1, -6.1, P = .005), smoking status (B coefficient -5.7, 95%CI -1.9, -9.5, P = .004), serum γ-glutamyl transferase (GGT) (B coefficient -0.04, 95%CI -0.05, -0.02, P < .0001), HMF (B coefficient -0.5, 95%CI -0.8, -0.1, P = .01) and diastolic function (B coefficient 0.1, 95%CI 0.05, 0.13, P < .0001) were independently associated with CRF. This model explained 60% of the total variance in CRF (R²  = 0.6, P < .0001); and this model with GGT alone explained 24% of the variance in CRF.

CONCLUSIONS

In patients with NAFLD, HMF is independently associated with CRF and a model with GGT alone explained most of the variance in CRF.

Visceral fat and cardiorespiratory fitness with prevalence of pre-diabetes/diabetes mellitus among middle-aged and elderly Japanese people: WASEDA'S Health Study

The relationships between cardiorespiratory fitness (CRF) measurements not confounded by adiposity and the prevalence of pre-diabetes mellitus (pre-DM) and diabetes mellitus (DM) are not well known. Thus, we aimed to investigate the associations of visceral fat (VF) and CRF with the prevalence of pre-DM/DM among Japanese adults. The study included 970 individuals (327 women and 643 men) who were 40-87 years old and had complete health examinations, abdominal fat area, and fitness data from WASEDA'S Health Study during 2015-2018. The VF area was measured using magnetic resonance imaging. CRF was measured using a cycle ergometer and was defined as VO2peak divided by fat free mass. The pre-DM/DM was identified based on the questionnaire and fasting blood tests. The odds ratios (ORs) and 95% confidence intervals (CIs) for prevalence of pre-DM/DM were calculated. Seventy-three participants had pre-DM and 48 participants had DM. Compared to the low VF group, the high VF group had a higher prevalence of pre-DM/DM (OR: 1.87, 95% CI: 1.18-2.96), although no significant relationship was observed between CRF and pre-DM/DM prevalence (P for trend = 0.239). The sub-group analyses also revealed no significant relationship between CRF and pre-DM/DM prevalence in the low VF group (P for trend = 0.979), although CRF values were inversely related to the prevalence of pre-DM/DM in the high VF group (P for trend = 0.024). Although CRF was not independently related to the prevalence of pre-DM/DM after adjusting for adiposity, higher VF values were related to a higher prevalence of pre-DM/DM. In addition, CRF levels were inversely associated with the prevalence of pre-DM/DM only among high VF individuals.

Quantification of Cardiorespiratory Fitness in Children with Obesity

PURPOSE

Without consideration for the effects of fat mass, there could be an underestimation of cardiorespiratory fitness in children with obesity leading to a clinical diagnosis of deconditioning and resulting in unrealistic training goals and limitation of physical activities. The purpose of this study was to identify methods of quantifying cardiorespiratory fitness that were less influenced by fat mass.

METHODS

Fifty-three children, 27 with obesity (10.9 ± 1.0 yr) and 26 without obesity (11.0 ± 1.0 yr), volunteered for this study. Maximal oxygen uptake, an indicator of cardiorespiratory fitness, was referenced to lean body mass, body mass, and predicted body mass at the 50th and 85th body mass index percentiles.

RESULTS

Children with obesity carried 18 kg more fat mass and 7 kg more lean body mass compared with children without obesity. Cardiorespiratory fitness based on lean body mass, body mass, and predicted body mass at the 85th percentile was lower in children with obesity compared with children without obesity (P < 0.001). Differences in cardiorespiratory fitness based on predicted body mass at the 50th percentile between children with and without obesity did not reach statistical significance (P = 0.84). Fat mass influenced cardiorespiratory fitness least when referenced to lean body mass or predicted body mass at the 50th percentile (R < 0.26) in contrast to when it was referenced to body mass or predicted body mass at the 85th percentile (R > 0.37).

CONCLUSION

Quantifying cardiorespiratory fitness based on lean body mass or predicted body mass at the 50th percentile could be useful for estimating fitness levels in children with obesity.

Early and asymptomatic cardiac dysfunction in chronic kidney disease

Background

Heart failure (HF) is highly prevalent and associated with high mortality in chronic kidney disease (CKD). However, the pathophysiology of cardiac dysfunction in CKD, especially in the early asymptomatic stage, is not well understood. We studied subclinical cardiac dysfunction in asymptomatic CKD patients without comorbid cardiac disease or diabetes mellitus by evaluating peak cardiac performance.

Methods

In a cross-sectional study (n = 130) we investigated 70 male non-diabetic CKD patients (21 CKD stage 2-3a, 27 CKD stage 3b-4 and 22 CKD stage 5) employing specialized cardiopulmonary exercise testing to measure peak cardiac output and cardiac power output non-invasively. Data from 35 age-matched healthy male volunteers were obtained for comparison. In addition, as a positive control, data from 25 age-matched male HF patients in New York Heart Association class II and III were also obtained.

Results

The study subjects showed a graded reduction in peak cardiac power, with 6.13 ± 1.11 W in controls, 5.02 ± 0.78 W in CKD 2-3a, 4.59 ± 0.53 W in CKD 3b-4 and 4.02 ± 0.73 W in CKD 5, although not as impaired as in HF, with 2.34 ± 0.63 W (all P < 0.005 versus control). The central haemodynamic characteristics of the cardiac impairment in CKD mirrored that of HF, with reduced flow and pressure-generating capacities, reduced chronotropic reserve and impaired contractility.

Conclusions

The study demonstrates for the first time impaired peak cardiac performance and cardiac functional reserve in asymptomatic CKD patients. The evidence of myocardial dysfunction in the absence of comorbid cardiac disease and diabetes warrants further evaluation of current pathophysiological concepts of cardiovascular disease in CKD.

Sex differences on peak oxygen uptake in heart failure

Women represent nearly half of the adult heart failure (HF) population and they remain underrepresented in HF studies. We aimed to evaluate the evidence about peak oxygen uptake (peak VO₂) for clinical stratification in women with HF. This narrative review summarizes (i) the evidence endorsing the value of cardiopulmonary exercise testing for clinical stratification and phenotyping HF population; (ii) the determinants of a person's functional aerobic capacity to understand predicted values for patients with chronic HF; and (iii) sex differences on peak VO₂ data in different forms of HF. Lastly, based on existing data in patients with HF, we provide a perspective on how to improve existing gaps about the utility of peak VO₂ in clinical stratification in women. Peak VO₂ provides prognosis information in patients with HF; however, its use has been limited for a reduced number of patients excluding women, elderly, and HF patients with preserved ejection fraction. Further studies will help to fill the wide gender gap about the utility of cardiopulmonary exercise testing in the risk assessment and management in women with HF.

Cardiorespiratory fitness, muscular strength and risk of type 2 diabetes: a systematic review and meta-analysis

AIMS/HYPOTHESIS

The study aimed to quantitatively summarise the dose-response relationships between cardiorespiratory fitness and muscular strength on the one hand and risk of type 2 diabetes on the other and estimate the hypothetical benefits associated with population-wide changes in the distribution of fitness.

METHODS

We performed a systematic review with meta-analysis. The PubMed and EMBASE electronic databases were searched from inception dates to 12 December 2018 for cohort studies examining the association of cardiorespiratory fitness or muscular strength with risk of incident type 2 diabetes in adults. The quality of included studies was evaluated using the Newcastle-Ottawa Scale.

RESULTS

Twenty-two studies of cardiorespiratory fitness and 13 studies of muscular strength were included in the systematic review with both exposures having ten estimates available for the primary adiposity- or body size-controlled meta-analysis. In random-effects meta-analysis including 40,286 incident cases of type 2 diabetes in 1,601,490 participants, each 1 metabolic equivalent (MET) higher cardiorespiratory fitness was associated with an 8% (95% CI 6%, 10%) lower RR of type 2 diabetes. The association was linear throughout the examined spectrum of cardiorespiratory fitness. In 39,233 cases and 1,713,468 participants each 1 SD higher muscular strength was associated with a 13% (95% CI 6%, 19%) lower RR of type 2 diabetes. We estimated that 4% to 21% of new annual cases of type 2 diabetes among 45-64-year-olds could be prevented by feasible and plausible population cardiorespiratory fitness changes.

CONCLUSIONS/INTERPRETATION

Relatively small increments in cardiorespiratory fitness and muscle strength were associated with clinically meaningful reductions in type 2 diabetes risk with indication of a linear dose-response relationship for cardiorespiratory fitness.

REGISTRATION

PROSPERO (CRD42017064526).

Associations of Cardiorespiratory Fitness and Adiposity With Arterial Stiffness and Arterial Dilatation Capacity in Response to a Bout of Exercise in Children

Purpose: To investigate the associations of directly measured peak oxygen uptake ( V˙O2peak ) and body fat percentage (BF%) with arterial stiffness and arterial dilatation capacity in children. Methods: Findings are based on 329 children (177 boys and 152 girls) aged 8-11 years. V˙O2peak was assessed by a maximal cardiopulmonary exercise test on a cycle ergometer and scaled by lean body mass (LM). BF% and LM were measured by bioelectrical impedance. Stiffness index (measure of arterial stiffness) and change in reflection index (ΔRI, measure of arterial dilatation capacity) were assessed by pulse contour analysis. Data were analyzed by linear regression models. Results:V˙O2peak/LM was positively associated with ΔRI in boys adjusted for age and BF% (β = 0.169, P = .03). Further adjustments for systolic blood pressure, heart rate, and the study group had no effect on this association, but additional adjustment for clinical puberty attenuated it (β = 0.171, P = .07). BF% was inversely related to ΔRI in boys adjusted for age and V˙O2peak/LM (β = -0.171, P = .03). V˙O2peak or BF% was not associated with ΔRI in girls or with stiffness index in either boys or girls. Conclusion: Increasing cardiorespiratory fitness and decreasing adiposity may improve arterial health in childhood, especially among boys.

Association between Protein-Bound Uremic Toxins and Asymptomatic Cardiac Dysfunction in Patients with Chronic Kidney Disease

Although the relationship between protein-bound uremic toxins (PBUTs) and cardiac structure and cardiac mortality in chronic kidney disease (CKD) has been studied in the past, the association between cardiac dysfunction and PBUTs has not yet been studied. We therefore evaluated the association between impaired peak cardiac performance and the serum free and total concentrations of potentially cardiotoxic PBUTs. In a cross-sectional study of 56 male CKD patients (stages 2–5 (pre-dialysis)) who were asymptomatic with no known cardiac diseases or diabetes we measured peak cardiac power (CPO_max), aerobic exercise capacity (VO_2max), and echocardiographic parameters of cardiac morphology and evaluated their association with PBUTs. The serum total and free concentrations of indoxyl sulfate (IXS), p-cresyl sulfate (PCS), p-cresyl glucuronide, indole acetic acid, and hippuric acid showed significant negative correlation with CPO_max and VO_2max. IXS and PCS were independently associated with CPO_max and VO_2max even after controlling for eGFR. No correlation between left ventricular mass index (LVMI) and PBUTs was seen. The present study for the first time has demonstrated the association between subclinical cardiac dysfunction in CKD and serum levels of a panel of PBUTs. Further studies are required to evaluate the mechanism of cardiotoxicity of the individual uremic toxins.

Cardiopulmonary fitness is strongly associated with body cell mass and fat-free mass: The Study of Health in Pomerania (SHIP)

Peak oxygen uptake (VO2peak) is commonly indexed by total body weight (TBW) to determine cardiopulmonary fitness (CPF). This approach may lead to misinterpretation, particularly in obese subjects. We investigated the normalization of VO2peak by different body composition markers. We analyzed combined data of 3848 subjects (1914 women; 49.7%), aged 20-90, from two independent cohorts of the population-based Study of Health in Pomerania (SHIP-2 and SHIP-TREND). VO2peak was assessed by cardiopulmonary exercise testing. Body cell mass (BCM), fat-free mass (FFM), and fat mass (FM) were determined by bioelectrical impedance analysis. The suitability of the different markers as a normalization variable was evaluated by taking into account correlation coefficients (r) and intercept (α-coefficient) values from linear regression models. A combination of high r and low α values was considered as preferable for normalization purposes. BCM was the best normalization variable for VO2peak (r = .72; P ≤ .001; α-coefficient = 63.3 mL/min; 95% confidence interval [CI]: 3.48-123) followed by FFM (r = .63; P ≤ .001; α-coefficient = 19.6 mL/min; 95% CI: -57.9-97.0). On the other hand, a much weaker correlation and a markedly higher intercept were found for TBW (r = .42; P ≤ .001; α-coefficient = 579 mL/min; 95% CI: 483 to 675). Likewise, FM was also identified as a poor normalization variable (r = .10; P ≤ .001; α-coefficient = 2133; 95% CI: 2074-2191). Sex-stratified analyses confirmed the above order for the different normalization variables. Our results suggest that BCM, followed by FFM, might be the most appropriate marker for the normalization of VO2peak when comparing CPF between subjects with different body shape.

The Obesity Factor: How Cardiorespiratory Fitness is Estimated More Accurately in People with Obesity

OBJECTIVE

Cardiopulmonary exercise testing is clinically used to estimate cardiorespiratory fitness (CRF). The relation to total body mass (TBM) leads to an underestimation of CRF in people with obesity and to inappropriate prognostic and therapeutic decisions. This study aimed to determine body composition-derived bias in the estimation of CRF in people with obesity.

METHODS

Two hundred eleven participants (58.8% women; mean BMI 35.7 kg/m² [± 6.94; 20.7-58.6]) were clinically examined, and body composition (InBody720; InBody Co., Ltd., Seoul, South Korea) and spiroergometrical peak oxygen consumption (VO₂ peak) were assessed. The impacts of TBM, lean body mass (LBM), and skeletal muscle mass (SMM) on CRF estimates were analyzed by the application of respective weight models. Linear regression and plotting of residuals against BMI were performed on the whole study population and two subgroups (BMI < 30 kg/m² and BMI ≥ 30 kg/m² ).

RESULTS

For every weight model, Δmean VO₂ peak (expected - measured) was positive. LBM and SMM had a considerable impact on VO₂ peak demand (P = 0.001; ΔR²  = 2.3%; adjusted R²  = 56% and P = 0.001; ΔR² = 2.7%; adjusted R²  = 56%), whereas TBM did not. Confounding of body composition on VO₂ peak did not differ in LBM and SMM.

CONCLUSIONS

TBM-adjusted overestimation of relative VO₂ demand is much higher in people with obesity than in those without. LBM or SMM adjustment may be superior alternatives, although small residual body composition-derived bias remains.

Cardiorespiratory Fitness and Adiposity as Determinants of Metabolic Health-Pooled Analysis of Two Twin Cohorts

Context

The joint effects of cardiorespiratory fitness (CRF) and body composition on metabolic health are not well known.

Objective

To examine the associations of CRF, fat-free mass index (FFMI), and fat mass index (FMI) with metabolic health in individual twins and controlling for genetic and shared environmental effects by studying monozygotic intrapair differences.

Design, Setting, and Participants

Two cross-sectional samples of healthy adult monozygotic and dizygotic twins were drawn from population-based Danish and Finnish national twin registries (n = 996 and n = 309).

Main Measures

CRF was defined as VO2max divided by fat-free mass. Insulin sensitivity and acute insulin response indices were derived from an oral glucose tolerance test. A continuous metabolic syndrome score was calculated. Visceral and liver fat were measured in the Finnish sample. Associations were analyzed separately in both cohorts with multivariate linear regression and aggregated with meta-analytic methods.

Results

Insulin sensitivity, acute insulin response, metabolic syndrome score, visceral, and liver fat amount had strong and statistically significant associations with FMI (|β| 0.53 to 0.79), whereas their associations with CRF and FFMI were at most weak (|β| 0.02 to 0.15). The results of the monozygotic intrapair differences analysis showed the same pattern.

Conclusions

Although FMI is strongly associated with worsening of metabolic health traits, even after controlling for genetic and shared environmental factors, there was little evidence for the effects of CRF or FFMI on metabolic health. This suggests that changing FMI rather than CRF or FFMI may affect metabolic health irrespective of genetic or early environmental determinants.

Cardiorespiratory fitness, respiratory function and hemodynamic responses to maximal cycle ergometer exercise test in girls and boys aged 9-11 years: the PANIC Study

PURPOSE

We aimed to provide comprehensive data on and reference values for cardiorespiratory fitness, respiratory function and hemodynamic responses during and after maximal cycle ergometer test in children.

METHODS

The participants were a population sample of 140 children (69 girls) aged 9-11 years. Heart rate (HR) and systolic blood pressure (SBP) were measured from pre-exercise rest to the end of recovery. Respiratory gases were measured directly by the breath-by-breath method. Peak workload, HR changes, peak oxygen uptake (VO2), peak oxygen pulse (O2 pulse), peak respiratory exchange ratio (RER) and the lowest ratio of ventilation and carbon dioxide output (VE/VCO2) during the exercise test in girls and boys were presented according to their distributions in 5 categories.

RESULTS

HR decreased more during 4-min recovery in boys than in girls (76 vs. 67 beats/min, p < 0.001), whereas SBP decrease was similar in boys and girls (30 vs. 22 mmHg, p = 0.66). Boys had a higher peak VO2 per weight [51.9 vs. 47.6 ml/kg/min, p < 0.001] and per lean mass [67.3 vs. 63.0 ml/kg/min, p < 0.001] than girls. Peak O2 pulse per lean mass was higher in boys than in girls (0.34 vs. 0.31 ml/kg/beat, p < 0.001). There was no difference in the lowest VE/VCO2 during the test between boys and girls (28 vs. 29, p = 0.18).

CONCLUSIONS

The indicators of cardiorespiratory fitness were better in boys than in girls. These data enable the evaluation of cardiorespiratory function during and after maximal exercise test and the detection of children with abnormal values.

Diet, insulin secretion and insulin sensitivity--the Dose-Responses to Exercise Training (DR's EXTRA) Study (ISRCTN45977199)

Intakes of saturated fat (SF) and dietary fibre, body mass and physical activity are all associated with the incidence of type 2 diabetes mellitus. Their relative importance for the maintenance of normal glucose metabolism is not fully known. In a population-based sample of 1114 individuals, aged 58-78 years, dietary intakes were assessed by 4 d food records and cardiorespiratory fitness as maximal oxygen uptake. Insulin secretion, insulin sensitivity, the early-phase disposition index (DI30) and the total disposition index (DI120) were assessed based on an oral glucose tolerance test. Linear associations were modelled using linear regression. Combined effects were studied by introducing SF and fibre intakes, as well as cardiorespiratory fitness and waist circumference (WC) as dichotomised variables in general linear models. Intakes of dietary fibre and whole-grain bread were positively associated with insulin sensitivity, independent of physical fitness and WC. In women, dietary fibre intake was also positively associated with DI30. The negative association of high WC with DI30 was attenuated by a combination of low SF intake and high cardiorespiratory fitness. In conclusion, dietary fibre and a combination of low SF intake and high cardiorespiratory fitness may contribute to the maintenance of normal glucose metabolism, independent of WC.

Measures of cardiorespiratory fitness in relation to measures of body size and composition among children

BACKGROUND

In the exercise testing measures of cardiorespiratory fitness need to be scaled by body size or composition to enable comparison between individuals. Traditionally used weight-proportional measures are potentially confounded by body adiposity that hampers their interpretation and applicability in the clinical assessment of cardiorespiratory fitness.

OBJECTIVE

We aimed to find the most appropriate measure of body size or composition for scaling of measures of cardiorespiratory fitness among children.

METHODS

We assessed body weight and height, maximal workload (W MAX ) and maximal oxygen uptake (VO2 MAX ) using cycle ergometer exercise test with respiratory gas analysis and body lean mass (LM) and fat mass (FM) by dual-energy X-ray absorptiometry and by bioimpedance analysis among 38 children. The data were analysed using Pearson's coefficients for correlation and stepwise linear regression models.

RESULTS

Lean mass (r > 0.54) and height (r > 0.51) had stronger positive correlations with absolute W MAX and VO2 MAX than weight (r > 0.30) in girls and boys. None of the measures of body size or composition correlated with LM-proportional W MAX or VO2 MAX in girls or boys. Only LM correlated positively with height-proportional W MAX (r = 0.65) and VO2 MAX (r = 0.71) in boys. FM correlated negatively with weight-proportional W MAX (r < -0.58) and VO2 MAX (r < -0.64) in girls and boys. FM was even stronger determinant of weight-proportional W MAX (β = -0.68) and VO2 MAX (β = -0.61) than exercise performance in multivariate linear regression models.

CONCLUSIONS

While assessing cardiorespiratory fitness, LM is the most appropriate measure of body size or composition for scaling of W MAX and VO2 MAX, because scaling by body weight introduces confounding by body adiposity.

Cardiovascular fitness and haemodynamic responses to maximal cycle ergometer exercise test in children 6-8 years of age

We investigated cardiovascular fitness and haemodynamic responses to maximal cycle ergometer exercise test in children. The participants were a population sample of 425 children (204 girls, 221 boys) aged 6-8 years. Heart rate (HR) and systolic blood pressure (SBP) were measured from the beginning of pre-exercise rest to the end of recovery period. We provided reference values for peak workload and changes in HR and SBP during and after maximal exercise test in girls and boys. Girls had a lower cardiovascular fitness, indicated by peak workload per body weight [mean (2 s) 2.7 (0.9) vs. 3.1 (1.0) W · kg(-1), P < 0.001] and lean mass [mean (2 s) 3.5 (0.9) vs. 3.8 (1.0) W · kg(-1), P < 0.001] than boys. Plateau or decline in SBP close to the end of the test was found in about third of children and was considered a normal SBP response. Girls had a slower HR decrease within 2 min after the test than boys [mean (2 s) 53 (18) vs. 59 (22) beats · min(-1), P < 0.001]. The results are useful for physicians and exercise physiologists to evaluate cardiovascular fitness and haemodynamic responses to exercise in children and to detect children with low exercise tolerance or abnormal haemodynamic responses to exercise.

The relationship between insulin sensitivity and maximal oxygen uptake is confounded by method of adjustment for body composition

BACKGROUND

The use of ratios for analyzing physiologic variables often creates spurious associations.

METHODS

Results of a euglycaemic clamp, a graded exercise test to measure maximal oxygen uptake (VO2max) and underwater weighing in 358 nondiabetic adults (166 women and 192 men) were used to compare the effects of weight standardization by division or by partial Spearman correlations on the association between VO2max and insulin sensitivity.

RESULTS

VO2max and insulin sensitivity were negatively correlated when VO2max was divided by weight. When partial Spearman correlations were used to adjust VO2max for body composition, the correlation between VO2max and insulin sensitivity was greatly diminished.

CONCLUSIONS

Division of VO2max by weight does not adjust for weight, but it creates spurious associations between VO2max and insulin sensitivity.

Dietary associations with prediabetic states--the DR's EXTRA Study (ISRCTN45977199)

BACKGROUND/OBJECTIVES

Impaired fasting plasma glucose (IFG) and impaired glucose tolerance (IGT) predict development of type 2 diabetes (T2D), but display different pathophysiology for T2D. We studied the association of selected food items and nutrients with IFG, IGT and combined IFG and IGT (IFG+IGT), independent of cardiorespiratory fitness (VO(2max)).

SUBJECTS/METHODS

In a population-based sample of 1261 individuals, aged 58-78 years, we identified 126 subjects with IFG, 97 with IGT and 49 with simultaneous IFG and IGT by an oral glucose tolerance test. Dietary intake was assessed by 4-day food records. Cardiorespiratory fitness was assessed by defining maximal oxygen uptake (VO(2max)) from respiratory gas analysis during a maximal symptom-limited exercise stress test on a bicycle ergometer.

RESULTS

Increased intake of saturated fat was associated with higher odds for IFG (OR 1.07; 1.01-1.14) after adjustment for age, gender, VO(2max) and energy misreporting variable. Consumption of additional whole-grain bread (50 g/1000 kcal) and intake of dietary fiber (g/1000 kcal) were inversely associated with IGT (OR 0.61; 0.41-0.92, OR 0.91; CI 0.85-0.97, respectively).

CONCLUSION

Dietary fiber and sources of cereal fiber are negatively associated with IGT, and saturated fat intake is positively associated with IFG, but not with IGT. The present data give practical dietary means at the population level for the elimination of prediabetic conditions.