Impact of exercise training on endothelial function and body composition in young people: a study of mono- and di-zygotic twins.

Flow mediated dilation (FMD) is a surrogate marker of arterial function which can be improved by exercise training. To date, no study has assessed the magnitude of FMD changes in response to exercise training between groups of mono- (MZ) and di-zygotic (DZ) twins. The purpose of this study was therefore to compare FMD in MZ- and DZ twins before and after identical exercise training interventions. At baseline, FMD was assessed using high resolution Duplex ultrasound in 12 twin pairs (6 MZ pairs 13.5 ± 0.8 years, 6 DZ pairs 13.4 ± 0.8 years). Twins completed 8 weeks of exercise training (65-85% HR(max)), consisting of three 45-min sessions per week. Change (Δ) scores were entered into twin versus twin intraclass correlation analyses by group. Change in %body fat (r = 0.63, P = 0.05) was significantly correlated in the MZ, but not the DZ group (r = 0.31, P = 0.23). Change in FMD was also highly correlated in MZ (r = 0.74, P = 0.02) but not in the DZ group (r = 0.37, P = 0.18). Heritability of ΔFMD was estimated at 0.74. Exercise induced changes in FMD were similar within sets of monozygotic twins but not dizygotic twins. These data suggest that a significant portion of the arterial function response to exercise training may be genetically determined.

The impact of exercise training on the diameter dilator response to forearm ischaemia in healthy men.

AIM: Recent studies found differences between groups in the rate of diameter increase following the flow-mediated dilation (FMD). Whilst exercise training alters the magnitude of the FMD, little is known about the impact of exercise training on the rate of diameter increase. The aim of this study is to examine post-cuff deflation changes in brachial artery diameter following 5 min forearm ischaemia every 2 weeks across 8-weeks of a handgrip exercise training regimen. METHODS: Post-deflation changes in brachial artery diameter following 5-min of ischaemia were examined before, after and every 2-weeks across an 8-week handgrip training programme in healthy young men (n = 11) using echo-Doppler. RESULTS: The magnitude of dilation increased at week 2-4-6, but returned towards baseline values at week 8 (anova: P = 8.001). The time-to-peak diameter (42 ± 15s) demonstrated a significant prolongation at week 4 (77 ± 32s), but returned towards baseline values at weeks 6 and 8 (anova: P < 0.001). The rate of diameter increase did not differ across the intervention. CONCLUSION: Exercise training in healthy subjects is initially characterized by a larger dilation. Since the rate of dilation did not change, a longer time-to-peak dilation was necessary to achieve the increase in magnitude of dilation. As exercise training continues, the timing and magnitude of the peak diameter response returns to near baseline levels.

Does brachial artery flow-mediated dilation scale to anthropometric characteristics?

Flow-mediated dilation (FMD) assesses the health of the vascular endothelium. Despite widespread adoption of scaling practices in cardiac research, scaling for body size or composition has not been used for FMD. The present study investigated the relationships between brachial FMD and body composition in 129 children aged 9-10 (75 female symbol, 54 male symbol), and 50 men aged 16-49. Body composition variables (total, lean, fat mass in the whole body, arm, forearm) were assessed by dual-energy X-ray absorptiometry, FMD was measured in the brachial artery using high-resolution ultrasound. FMD was scaled using simple ratios (y/x) and allometric approaches (y/x ( b )) after log-log least squares linear regression produced allometric exponents (b). Size independence was confirmed via bivariate correlations (x:y/x; x:y/x ( b )). No relationships were evident between FMD and body composition variables in adults. Small correlations existed between FMD and measures of segmental fat mass in children (r = -0.18 to -0.19, p < 0.05), there were no significant relationships between FMD and measures of lean or total mass in children. For all significant relationships, b-exponents were different from 1 (CIs -0.36 to 0.07), suggesting ratio scaling approaches were flawed. This was confirmed when ratio scaling produced negative residual size correlations, whereas allometric scaling produced size-independent indices. Correlations between FMD and body composition were weak in children and insignificant in adults. As the results of this study are limited to the populations examined, our findings do not support the adoption of scaling procedures to correct FMD.

Does conduit artery diameter vary according to the anthropometric characteristics of children or men?

Arterial measurements are commonly undertaken to assess acute and chronic adaptations to exercise. Despite the widespread adoption of scaling practices in cardiac research, the relevance of scaling for body size and/or composition has not been addressed for arterial measures. We therefore investigated the relationships between brachial artery diameter and body composition in 129 children aged 9 to 10 yr (75 girls and 54 boys), and 50 men aged 16-49 yr. Body composition variables (total, lean, and fat mass in the whole body, arm, and forearm) were assessed by dual-energy X-ray absorptiometry, and brachial artery diameter was measured using high-resolution ultrasound. Bivariate correlations were performed, and arterial diameter was then scaled using simple ratios (y/x) and allometric approaches after log-log least squares linear regression and production of allometric exponents (b) and construction of power function ratios (y/xb). Size independence was checked via bivariate correlations (x:y/x; x:y/xb). As a result, significant correlations existed between brachial artery diameter and measures of body mass and lean mass in both cohorts (r=0.21-0.48, P<0.05). There were no significant relationships between diameter and fat mass. All b exponents were significantly different from 1 (0.08-0.50), suggesting that simple ratio scaling approaches were likely to be flawed. This was confirmed when ratio scaling produced negative residual size correlations, whereas allometric scaling produced size-independent indexes (r=0.00 to 0.03, P>0.05). In conclusion, when between- or within-group comparisons are performed under circumstances where it is important to control for differences in body size or composition, allometric scaling of artery diameter should be adopted rather than ratio scaling. Our data also suggest that scaling for lean or total mass may be more appropriate than scaling for indexes of fat mass.

Relationships between measures of fitness, physical activity, body composition and vascular function in children.

BACKGROUND: The prevalence of obesity and physical inactivity in Western countries has increased rapidly. Both are modifiable risk factors for cardiovascular disease. Atherosclerosis begins in childhood and endothelial dysfunction is its earliest detectable manifestation. METHODS: We assessed flow-mediated dilation (FMD) in 129 children (75 female; 10.3+0.3 yrs; 54 male; 10.4; 0.3 yrs). FMD was normalised for differences in the eliciting shear rate stimulus between subjects (SR(AUC)). Fitness was assessed as peak oxygen uptake during an incremental treadmill exercise test (V O(2)peak). Body composition was measured using a dual-energy X-ray absorptiometry (DEXA) scan. Physical activity (PA) was assessed using Actigraph accelerometers. The cohort was split into tertiles according to FMD% and also FMD% corrected for SR(AUC) to gain insight into the determinants of vascular function. RESULTS: Across the cohort, significant correlations were observed between FMD%/SR(AUC) and DEXA percentage fat (r=-0.23, p=0.009) and percentage lean mass (r=0.21, p=0.008), and also with PA performed at moderate-to-high intensity (r=0.363, p=0.001). For children in the lowest FMD%/SR(AUC) tertile, a stronger relationship with all PA measures was observed, particularly with high intensity PA (r=0.572, P=0.003). Regression analysis revealed that high intensity PA was the only predictor of impaired FMD%/SR(AUC). CONCLUSIONS: These data suggest that traditional risk factors for CHD in adult populations impact upon vascular function in young people. Furthermore, it appears that individuals with impaired FMD may benefit from performing high intensity PA, whereas no relationships exist between FMD and lower intensities of PA or between PA and FMD in those subjects who possess preserved vascular function a priori.