Association of objectively measured physical activity with vascular endothelial function in male adolescents

Purpose: Cardiovascular disease (CVD) begins in childhood primarily due to exposure to lifestyle-mediated risk factors such as inactivity and low cardiorespiratory fitness (CRF). Endothelial dysfunction is one of the earliest events in the development of CVD. Self-reported light intensity physical activity (LIPA) is positively associated with endothelial function (EF) in adolescents. The purpose of this study was to examine the relation between objectively measured physical activity (PA) and EF in healthy male adolescents. Methods: Low (n=8, VO2max = 40.4 ± 2.3 mL.kg1.min-1), moderate CRF (n=12,VO2max = 54.6 ± 3.9 mL.kg1.min-1) and high CRF (n=15, VO2max = 63.7 ± 4.0 mL.kg1.min-1) healthy males (mean age 15.77 ± 0.4; yr) participated in the study. High-resolution ultrasonography was used to assess endothelial dependent (EDD) in response to brachial artery flow mediated dilation. Participants wore a tri-axial ActivPAL accelerometer for 6 days. Total time spent in sitting, standing, LIPA, moderate-vigorous PA (MVPA) and steps per day was calculated using previously published methodology (Dowd et al., 2012). Results: EDD was significantly lower in low CRF than the high CRF group. Steps per day were significantly lower in low CRF (9251 ± 4113) than high CRF group (14007 ± 3176) (p<0.005). Time in sitting was significantly higher in low CRF than high CRF group (p<0.028). MVPA was significantly lower in low CRF than high CRF group (p<0.01). There was no significant difference in standing and LIPA between the groups. There was a significant positive relation between steps per day and % change (r=0.54, p<0.001) and absolute change in EDD (r= 0.60, p<0.001). Sitting was inversely related to % change (r=-0.497, p< 0.002) and absolute change in EDD (r=-0.49, p<0.003). There was a significant positive relation between MVPA and % change (r=0.47, p<0.005) and absolute change in EDD (r=0.57 p<0.000). Conclusion: There was a significant difference in steps per day, time spent sitting and in MVPA between low CRF and high CRF. MVPA was positively associated with EF in healthy adolescent males

Cardiorespiratory fitness, oxygen uptake efficency slope and endothelial function in male adolescents

Cardiorespiratory fitness (CRF) is a independent risk factor for CVD and all-cause mortality. Maximal oxygen uptake (VO2max), is considered the gold standard measurement of CRF. Due to its effort dependency, a true plateau in VO2 during incremental exercise is often not attained, particularly in overweight and obese pediatric populations 1. The oxygen uptake efficiency slope (OUES) has been proposed as an objective and effort independent submaximal measure of cardiopulmonary reserve. Studies in healthy and obese children have reported a strong positive relation between OUES and VO2max. Children with high CRF have higher OUES values than those with low CRF 2. Furthermore, improvements in CRF following exercise training, are associated with restoration of endothelial function (EF) in obese children 3. The purpose of this study was to examine the relation between OUES, VO2max and EF in healthy male adolescents. ad

Cardiorespiratory fitness, physical activity, sedentary behaviour and vascular health in male adolescents

Study 1: A high cardiorespiratory fitness (CRF) level is positively associated with a more favorable cardiometabolic health profile in adolescents. Limited information exists on the relation between CRF and vascular health in healthy adolescents. The purpose of this study was to compare cardiovascular disease (CVD) risk factors and vascular health in healthy low fit (LF), moderate fit (MF) and high fit (HF) male adolescents. LF male adolescents had significantly poorer endothelial dependent dilation (EDD) and cardiovascular health profile and significantly higher carotid intima media thickness (cIMT) compared to both MF and LF. There was a significant positive relation between V̇O2max and EDD and a significant inverse association between V̇O2max and cIMT in healthy male adolescents. Study 2: The oxygen uptake efficiency slope (OUES) has been proposed as an objective and effort independent submaximal measure of CRF and may serve as an alternative to V̇O2max when assessing CRF in adolescents. This study evaluated OUES and vascular health in LF, MF and HF healthy male adolescents with low, moderate and high CRF. Maximal and submaximal OUES expressed relative to body weight were significantly higher in HF than both MF and LF. There was a significant positive relation between both maximal and submaximal OUES and EDD and a significant inverse relation between maximal and submaximal OUES and cIMT. In a stepwise multiple linear regression analysis that included V̇O2max, maximal OUES and submaximal OUES, only V̇O2max was a significant predictor of EDD. Study 3: This study compared physical activity (PA) levels, sedentary behaviour, CVD risk factors and vascular health in LF, MF and HF apparently healthy male adolescents. Time spent in moderate-to-vigorous PA (MVPA) was significantly higher and time spent sitting/lying was significantly lower in HF than both MF and LF. Time spent in light intensity PA (LIPA) was significantly higher in HF than LF. Time in MVPA and LIPA were both significantly and positively related with EDD and inversely related to cIMT. There was a significant inverse relation between time sitting/lying and EDD and a significant positive relation between time sitting/lying and cIMT. Conclusion: cIMT was significantly higher and EDD was significantly lower in LF than both MF and HF. While OUES, PA and sedentary time were all significantly related to markers of vascular health, a more robust relation was observed between V̇O2max and vascular health. Furthermore, V̇O2max was independently related to EDD and cIMT

Cardiorespiratory fitness and vascular health in youth

CVD refers to disease of the heart and blood vessels and is the leading cause of mortality in Ireland. CVD Begins in childhood and adolescence due primarily to exposure to lifestyle mediated risk factors . Endothelail dysfunction, induced by CVD risk factors, is one of the earliest events in the development of CVD and precedes structural changes in the artery walll such as intima media thickness. Exercise training has been shown to restrore endothelial function (EF), decrease carotid intima media thickness (cIMT) and improve CV risk profile in obese children. There is currently no research that has examined subclinical atherosclerotic CVD in asympomatic adolescents with low and high cardiorepsiratory fitness (CRF). This study compared CVD risk factors, cIMT and EF in adolescent boys with low and high CRF and examined the relation between CRF and cIMT and CRF and FMD in asympomatic adolescent boys. It was hypothesised that boys with a high CRF would have a healthier CV profile and that there would be an inverse relation between CRF and cIMT and CRF and EF

Effect of lower body negative pressure on physiological, perceptual and affective responses during self regulated exercise

Purpose: Lower body negative pressure (LBNP) treadmill exercise was developed for health maintenance during periods of microgravity. It involves exercising on a treadmill within a waist-high pressure chamber connected to a pump. LBNP treadmill exercise generates a pressure differential between the upper and lower body increasing ground reaction forces (GRFs). This study compared the physiological, perceptual and affective responses in women during 30 min of self-regulated treadmill walking with and without LBNP

Maximal oxygen consumption and oxygen uptake efficiency in adolescent males

Background/Objective Measures of oxygen uptake efficiency (OUE) have been used to evaluate cardiorespiratory fitness (CRF) in adolescents unable to perform maximal exercise. The oxygen uptake efficiency slope (OUES) and oxygen uptake efficiency plateau (OUEP) have been proposed as surrogates for maximal oxygen consumption (V̇O 2max ). We assessed the validity of the OUES and OUEP as predictors of V̇O 2max in healthy male adolescents. Methods Sixty-three healthy male adolescents aged 15.40 ± 0.34 years underwent an incremental treadmill test to determine V̇O 2max , OUES and OUEP. OUE throughout the test was assessed by dividing each V̇O 2 value by the corresponding minute ventilation (V̇ E ) value. OUEP was determined as the 90 sec average highest consecutive values for OUE. OUES was determined using data up to the ventilatory threshold (VT) by calculating the slope of the linear relation between V̇O 2 and the logarithm of V̇ E . Results Limits of agreement for V̇O 2max predicted by OUES (± 13.3 mL.kg -1 .min -1 ) and OUEP (± 16.7 mL.kg -1 .min -1 ) relative to V̇O 2max were wide and a magnitude bias was found for OUES and OUEP as predictors of V̇O 2max (p<0.001). Conclusion The OUES and OUEP do not accurately predict V̇O 2max in male adolescents and should not replace V̇O 2max when assessing CRF in this population

Platelets: Functional Biomarkers of Epigenetic Drift

Cardiovascular disease (CVD) risk factors can be classed as modifiable or non-modifiable. Physical inactivity and obesity represent major behavioural risk factors for the initiation, development and progression of CVD. Platelet dysfunction is pivotal to the aetiology of CVD, a chronic vascular inflammatory condition, which is characterised by a lag time between onset and clinical manifestation. This indicates the role of epigenetic drift, defined by stochastic patterns of gene expression not dependent on dynamic changes in coding DNA. The epigenome, a collection of chemical marks on DNA and histones, is established during embryogenesis and modified by age and lifestyle. Biogenesis and effector function of non-coding RNA, such as microRNA, play a regulatory role in gene expression and thus the epigenetic mechanism. In this chapter, we will focus on the effect of the modifiable risk factors of physical activity/inactivity and overweight/obesity on platelet function, via epigenetic changes in both megakaryocytopoiesis and thrombopoiesis. We will also discuss the role of acute exercise on platelet function and the impact of cardiorespiratory fitness (CRF) on platelet responses to acute exercise. This chapter will highlight the potential role of platelets as circulating functional biomarkers of epigenetic drift to implement, optimise and monitor CVD preventive management strategies

Platelets: From Formation to Function

Platelets are small, anucleate cells that travel as resting discoid fragments in the circulation. Their average circulating life span is 8–9 days, and their formation is an elegant and finely orchestrated series of cellular processes known as megakaryocytopoiesis and thrombopoiesis. This involves the commitment of haematopoietic stem cells, proliferation, terminal differentiation of megakaryocytic progenitors and maturation of megakaryocytes to produce functional platelets. This complex process occurs in specialised endosteal and vascular niches in the bone marrow where megakaryocytes form proplatelet projections, releasing platelets into the circulation. Upon contact with an injured blood vessel, they prevent blood loss through processes of adhesion, activation and aggregation. Platelets play a central role in cardiovascular disease (CVD), both in the development of atherosclerosis and as the cellular mediator in the development of thrombosis. Platelets have diverse roles not limited to thrombosis/haemostasis, also being involved in many vascular inflammatory conditions. Depending on the physiological context, platelet functions may be protective or contribute to adverse thrombotic and inflammatory outcomes. In this chapter, we will discuss platelets in context of their formation and function. Because of their multifaceted role in maintaining physiological homeostasis, current and development of platelet function testing platforms will be discussed