Cardiac output and stroke volume changes with endurance training: the HERITAGE Family Study

Effects of aging and endurance exercise training on cardiorespiratory fitness and cardiac structure and function in healthy midlife and older women

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality in women in developed societies. Unfavorable structural and functional adaptations within the heart and central blood vessels with sedentary aging in women can act as the substrate for the development of debilitating CVD conditions such as heart failure with preserved ejection fraction (HFpEF). The large decline in cardiorespiratory fitness, as indicated by maximal or peak oxygen uptake (V̇o2max and V̇o2peak, respectively), that occurs in women as they age significantly affects their health and chronic disease status, as well as the risk of cardiovascular and all-cause mortality. Midlife and older women who have performed structured endurance exercise training for several years or decades of their adult lives exhibit a V̇o2max and cardiac and vascular structure and function that are on par or even superior to much younger sedentary women. Therefore, regular endurance exercise training appears to be an effective preventative strategy for mitigating the adverse physiological cardiovascular adaptations associated with sedentary aging in women. Herein, we narratively describe the aging and short- and long-term endurance exercise training adaptations in V̇o2max, cardiac structure, and left ventricular systolic and diastolic function at rest and exercise in midlife and older women. The role of circulating estrogens on cardiac structure and function is described for consideration in the timing of exercise interventions to maximize beneficial adaptations. Current research gaps and potential areas for future investigation to advance our understanding in this critical knowledge area are highlighted.

Moderate to Vigorous-intensity Continuous Training versus High-intensity Interval Training for improving VO2max in women: A systematic review and meta-analysis

Traditional continuous training and high-intensity interval training (HIIT) can increase maximal oxygen uptake (V̇O_2max). However, there is conflicting evidence regarding which form of training demonstrates the greatest improvements to V̇O_2max, and data in women is sparse. We conducted a systematic review and meta-analyses to assess whether moderate to vigorous-intensity continuous training (MVICT) or HIIT was superior at improving V̇O_2max in women. Randomised controlled and parallel studies examined the influence of MVICT and/or HIIT on V̇O_2max in women. There was no statistical difference in V̇O_2max improvements after training between women in the MVICT and HIIT cohorts (mean difference [MD]: -0.42, 95%CI: -1.43 to 0.60, p>0.05). Both MVICT and HIIT increased V̇O_2max from baseline (MD: 3.20, 95% CI: 2.73 to 3.67 and MD: 3.16, 95% CI 2.09 to 4.24, respectively, p<0.001). Greater improvements in V̇O_2max were observed in women who participated in more training sessions in both training formats. Long-HIIT was superior to short-HIIT protocols at increasing V̇O_2max. Although MVICT and long-HIIT sessions elicited greater increases in V̇O_2max in younger women compared to short-HIIT protocols, these differences were negligible in older women. Our findings suggest MVICT and HIIT are equally effective strategies for improving V̇O_2max and indicate an effect of age on its response to training in women.

The Health Effects of 14 Weeks of Physical Activity in a Real-Life Setting for Adults with Intellectual Disabilities

Background

The life expectancy of individuals with intellectual disabilities (ID) is reduced compared to the general population, and one of the main contributors to earlier death is inactivity.

Aim

To investigate how 14 weeks of physical activity (PA) in a real-life setting affects cardiovascular fitness, body composition and bone health of adults with ID.

Methods

Adults with ID were recruited into a PA-group (N = 52) or a control group (CON, N = 14). The PA-group participated in 14 weeks of PA, and body composition, cardiovascular fitness and bone health were assessed before and after the intervention. Outcomes and Results. Cardiovascular fitness and body composition improved from pre to post within the PA-group: Heart rates (HR) during the last 30 seconds of two increments of a treadmill test, were reduced (3.2 km/h: -4.4 bpm, p < 0.05; 4.8 km/h: -7.5 bpm, p < 0.001) and fat mass was reduced (-1.02 kg, p < 0.05). A between-group difference in favour of the PA-group, were observed in whole body bone mineral density (BMD) (0.024 g/cm2, p < 0.05). Conclusions and Implications. Fourteen weeks of PA performed in a real-life setting increased cardiovascular fitness, reduced fat mass and improved BMD in the weight-bearing skeleton in the PA-group. Increased and regular PA seems to be a promising tool to promote physical health in adults with ID.

Cardiopulmonary capacity and muscle strength in transgender women on long-term gender-affirming hormone therapy: a cross-sectional study

OBJECTIVE

For transgender women (TW) on oestrogen therapy, the effects of prior exposure to testosterone during puberty on their performance, mainly cardiopulmonary capacity (CPC), while exerting physical effort are unknown. Our objective was to evaluate CPC and muscle strength in TW undergoing long-term gender-affirming hormone therapy.

METHODS

A cross-sectional study was carried out with 15 TW (34.2±5.2 years old), 13 cisgender men (CM) and 14 cisgender women (CW). The TW received hormone therapy for 14.4±3.5 years. Bioimpedance, the hand grip test and cardiopulmonary exercise testing on a treadmill with an incremental effort were performed.

RESULTS

The mean VO2peak (L/min) was 2606±416.9 in TW, 2167±408.8 in CW and 3358±436.3 in CM (TW vs CW, p<0.05; TW vs CM, p<0.0001; CW vs CM, p<0.0001). The O2 pulse in TW was between that in CW and CM (TW vs CW, p<0.05, TW vs CM, p<0.0001). There was a high correlation between VO2peak and fat-free mass/height² among TW (r=0.7388; p<0.01), which was not observed in the other groups. The mean strength (kg) was 35.3±5.4 in TW, 29.7±3.6 in CW and 48.4±6.7 in CM (TW vs CW, p<0.05; TW vs CM, p<0.0001).

CONCLUSION

CPC in non-athlete TW showed an intermediate pattern between that in CW and CM. The mean strength and VO2 peak in non-athlete TW while performing physical exertion were higher than those in non-athlete CW and lower than those in CM.

The HERITAGE Family Study: A Review of the Effects of Exercise Training on Cardiometabolic Health, with Insights into Molecular Transducers

The aim of the HERITAGE Family Study was to investigate individual differences in response to a standardized endurance exercise program, the role of familial aggregation, and the genetics of response levels of cardiorespiratory fitness and cardiovascular disease and diabetes risk factors. Here we summarize the findings and their potential implications for cardiometabolic health and cardiorespiratory fitness. It begins with overviews of background and planning, recruitment, testing and exercise program protocol, quality control measures, and other relevant organizational issues. A summary of findings is then provided on cardiorespiratory fitness, exercise hemodynamics, insulin and glucose metabolism, lipid and lipoprotein profiles, adiposity and abdominal visceral fat, blood levels of steroids and other hormones, markers of oxidative stress, skeletal muscle morphology and metabolic indicators, and resting metabolic rate. These summaries document the extent of the individual differences in response to a standardized and fully monitored endurance exercise program and document the importance of familial aggregation and heritability level for exercise response traits. Findings from genomic markers, muscle gene expression studies, and proteomic and metabolomics explorations are reviewed, along with lessons learned from a bioinformatics-driven analysis pipeline. The new opportunities being pursued in integrative -omics and physiology have extended considerably the expected life of HERITAGE and are being discussed in relation to the original conceptual model of the study.

Exercise during Pregnancy: Developmental Programming Effects and Future Directions in Humans

Epidemiological studies show that low birth weight is associated with mortality from cardiovascular disease in adulthood, indicating that chronic diseases could be influenced by hormonal or metabolic insults encountered in utero. This concept, now known as the Developmental Origins of Health and Disease hypothesis, postulates that the intrauterine environment may alter the structure and function of the organs of the fetus as well as the expression of genes that impart an increased vulnerability to chronic diseases later in life. Lifestyle interventions initiated during the prenatal period are crucial as there is the potential to attenuate progression towards chronic diseases. However, how lifestyle interventions such as physical activity directly affect human offspring metabolism and the potential mechanisms involved in regulating metabolic balance at the cellular level are not known. The purpose of this review is to highlight the effects of exercise during pregnancy on offspring metabolic health and emphasize gaps in the current human literature and suggestions for future research.

Effect of Exercise-Induced Reductions in Blood Volume on Cardiac Output and Oxygen Transport Capacity

We wanted to demonstrate the relationship between blood volume, cardiac size, cardiac output and maximum oxygen uptake (V.O_2max) and to quantify blood volume shifts during exercise and their impact on oxygen transport. Twenty-four healthy, non-smoking, heterogeneously trained male participants (27 ± 4.6 years) performed incremental cycle ergometer tests to determine V.O_2max and changes in blood volume and cardiac output. Cardiac output was determined by an inert gas rebreathing procedure. Heart dimensions were determined by 3D echocardiography. Blood volume and hemoglobin mass were determined by using the optimized CO-rebreathing method. The V.O_2max ranged between 47.5 and 74.1 mL⋅kg^–1⋅min^–1. Heart volume ranged between 7.7 and 17.9 mL⋅kg^–1 and maximum cardiac output ranged between 252 and 434 mL⋅kg^–1⋅min^–1. The mean blood volume decreased by 8% (567 ± 187 mL, p = 0.001) until maximum exercise, leading to an increase in [Hb] by 1.3 ± 0.4 g⋅dL^–1 while peripheral oxygen saturation decreased by 6.1 ± 2.4%. There were close correlations between resting blood volume and heart volume (r = 0.73, p = 0.002), maximum blood volume and maximum cardiac output (r = 0.68, p = 0.001), and maximum cardiac output and V.O_2max (r = 0.76, p < 0.001). An increase in maximum blood volume by 1,000 mL was associated with an increase in maximum stroke volume by 25 mL and in maximum cardiac output by 3.5 L⋅min^–1. In conclusion, blood volume markedly decreased until maximal exhaustion, potentially affecting the stroke volume response during exercise. Simultaneously, hemoconcentrations maintained the arterial oxygen content and compensated for the potential loss in maximum cardiac output. Therefore, a large blood volume at rest is an important factor for achieving a high cardiac output during exercise and blood volume shifts compensate for the decrease in peripheral oxygen saturation, thereby maintaining a high arteriovenous oxygen difference.

Genetic approaches toward understanding the individual variation in cardiac structure, function and responses to exercise training

Cardiovascular disease (CVD) accounts for approximately 30% of all deaths worldwide and its prevalence is constantly increasing despite advancements in medical treatments. Cardiac remodeling and dysfunction are independent risk factors for CVD. Recent studies have demonstrated that cardiac structure and function are genetically influenced, suggesting that understanding the genetic basis for cardiac structure and function could provide new insights into developing novel therapeutic targets for CVD. Regular exercise has long been considered a robust non-therapeutic method of treating or preventing CVD. However, recent studies also indicate that there is inter-individual variation in response to exercise. Nevertheless, the genetic basis for cardiac structure and function as well as their responses to exercise training have yet to be fully elucidated. Therefore, this review summarizes accumulated evidence supporting the genetic contribution to these traits, including findings from population-based studies and unbiased large genomic-scale studies in humans.

Sustained high levels of physical activity lead to improved performance among "Race Across the USA" athletes

OBJECTIVE

To investigate physiological and performance adaptations associated with extremely high daily sustained physical activity levels, we followed six runners participating in the 2015 Race Across the USA. Participants completed over 42.2 km a day for 140 days, covering nearly 5,000 km. This analysis examines the improvement in running speed and potential adaptation in mean submaximal heart rate (SHR) throughout the race.

METHODS

Data were collected during three 1-week long periods corresponding to the race beginning, middle, and end and included heart rates (HRs), body mass, running distances and speeds. HR data were collected using ActiTrainer HR monitors. Running speeds and distances were also recorded throughout the entire race.

RESULTS

Athletes ran significantly faster as the race progressed (p < .001), reducing their mean marathon time by over 63 min. Observed mean SHR during the middle of the race was significantly lower than at the beginning (p = .003); however, there was no significant difference between mean SHR at the middle and end of the race (p = .998).

CONCLUSION

These results indicate an early training effect in SHR during the first half of the race, which suggests that other physiological and biomechanical mechanisms were responsible for the continued improvement in running speed and adaptation to the high levels of sustained physical activity.

Sex-Specific Ventricular and Vascular Adaptations to Exercise

Increasing data suggest that there are sex differences in ventricular and vascular adaptations to aerobic (endurance) exercise, which may be attributed to different physical and physiological features in men and women. Despite that cardiovascular control during acute exercise at the same relative work rate (e.g., the percentage of peak oxygen uptake) appears to be similar between the sexes, women have blunted responses or adaptations to prolonged (e.g., ≥1 year) exercise training compared with men. Currently, there is little evidence to suggest that exercise-induced vascular adaptations are different between men and women. Furthermore, sex differences in skeletal muscle adaptations to exercise, and how this influences cardiovascular function, remain unclear. Identifying potential differences and the mechanisms behind such exercise-induced adaptations is important for the optimization of exercise interventions between men and women across the life span.

Aerobic interval training reduces vascular resistances during submaximal exercise in obese metabolic syndrome individuals

PURPOSE

The aim of this study was to determine the effects of high-intensity aerobic interval training (AIT) on exercise hemodynamics in metabolic syndrome (MetS) volunteers.

METHODS

Thirty-eight, MetS participants were randomly assigned to a training (TRAIN) or to a non-training control (CONT) group. TRAIN consisted of stationary interval cycling alternating bouts at 70-90% of maximal heart rate during 45 min day^-1 for 6 months.

RESULTS

CONT maintained baseline physical activity and no changes in cardiovascular function or MetS factors were detected. In contrast, TRAIN increased cardiorespiratory fitness (14% in VO_2PEAK; 95% CI 9-18%) and improved metabolic syndrome (-42% in Z score; 95% CI 83-1%). After TRAIN, the workload that elicited a VO₂ of 1500 ml min^-1 increased 15% (95% CI 5-25%; P < 0.001). After TRAIN when subjects pedaled at an identical submaximal rate of oxygen consumption, cardiac output increased by 8% (95% CI 4-11%; P < 0.01) and stroke volume by 10% (95% CI, 6-14%; P < 0.005) being above the CONT group values at that time point. TRAIN reduced submaximal exercise heart rate (109 ± 15-106 ± 13 beats min^-1; P < 0.05), diastolic blood pressure (83 ± 8-75 ± 8 mmHg; P < 0.001) and systemic vascular resistances (P < 0.01) below CONT values. Double product was reduced only after TRAIN (18.2 ± 3.2-17.4 ± 2.4 bt min^-1 mmHg 10^-3; P < 0.05).

CONCLUSIONS

The data suggest that intense aerobic interval training improves hemodynamics during submaximal exercise in MetS patients. Specifically, it reduces diastolic blood pressure, systemic vascular resistances, and the double product. The reduction in double product, suggests decreased myocardial oxygen demands which could prevent the occurrence of adverse cardiovascular events during exercise in this population. CLINICALTRIALS.

GOV IDENTIFIER

NCT03019796.

Physical activity levels determine exercise-induced changes in brain excitability

Emerging evidence suggests that regular physical activity can impact cortical function and facilitate plasticity. In the present study, we examined how physical activity levels influence corticospinal excitability and intracortical circuitry in motor cortex following a single session of moderate intensity aerobic exercise. We aimed to determine whether exercise-induced short-term plasticity differed between high versus low physically active individuals. Participants included twenty-eight young, healthy adults divided into two equal groups based on physical activity level determined by the International Physical Activity Questionnaire: low-to-moderate (LOW) and high (HIGH) physical activity. Transcranial magnetic stimulation was used to assess motor cortex excitability via motor evoked potential (MEP) recruitment curves for the first dorsal interosseous (FDI) muscle at rest (MEP_REST) and during tonic contraction (MEP_ACTIVE), short-interval intracortical inhibition (SICI) and facilitation (SICF), and intracortical facilitation (ICF). All dependent measures were obtained in the resting FDI muscle, with the exception of AMT and MEP_ACTIVE recruitment curves that were obtained during tonic FDI contraction. Dependent measures were acquired before and following moderate intensity aerobic exercise (20 mins, ~60% of the age-predicted maximal heart rate) performed on a recumbent cycle ergometer. Results indicate that MEP_REST recruitment curve amplitudes and area under the recruitment curve (AURC) were increased following exercise in the HIGH group only (p = 0.002 and p = 0.044, respectively). SICI and ICF were reduced following exercise irrespective of physical activity level (p = 0.007 and p = 0.04, respectively). MEP_ACTIVE recruitment curves and SICF were unaltered by exercise. These findings indicate that the propensity for exercise-induced plasticity is different in high versus low physically active individuals. Additionally, these data highlight that a single session of aerobic exercise can transiently reduce inhibition in the motor cortex regardless of physical activity level, potentially priming the system for plasticity induction.

Influence of the Type of Training Sport Practised on Psychological and Physiological Parameters during Exhausting Endurance Exercises

The present purpose was to study the influence of the type of training sport practised (long distance running, sprinting, handball) on ratings of perceived exertion (RPE), estimation of time limit (ETL), and heart rate (HR) on running tests. It was hypothesised that these parameters would be related to the type of training sport practised. 31 trained women (10 endurance-trained runners, 10 sprinters, and 11 handball players) performed two exercises to exhaustion on an outdoor track. The first test was a graded run to estimate maximal aerobic speed (SMA), i.e., the minimal speed which elicited maximal oxygen uptake. The second test was a constant all-out run at speed delta 50 (SΔ50), which corresponded to the speed halfway between SMA and the speed at lactate threshold (SLT), to specify time to exhaustion at this intensity (TLIM). Sensations regarding RPE, ETL, and HR were recorded during these tests. SMA, SΔ50, and SLT, expressed in absolute values (km · hr.−1) were statistically significantly different between groups ( p<.05) whereas TLIM was not. The covariance analysis showed that endurance-trained runners perceived the exercise as lighter and presented lower HR than handball players and sprinters for a same running %SMA ( p<.05). Moreover, endurance-trained runners felt that they could endure more than the other groups at a given %SMA or relative exhaustion time (%TLIM). These results mean that the type of training sport which has been performed may mediate perceptual responses and influence physiological parameters during exhausting exercises. These results are likely in part related to sport-specificity of the exercise mode used in tests. This point must be taken into consideration by physical trainers who have to prescribe exercise intensities during athletic seasons for different groups of athletes.

Regulation of increased blood flow (hyperemia) to muscles during exercise: a hierarchy of competing physiological needs

This review focuses on how blood flow to contracting skeletal muscles is regulated during exercise in humans. The idea is that blood flow to the contracting muscles links oxygen in the atmosphere with the contracting muscles where it is consumed. In this context, we take a top down approach and review the basics of oxygen consumption at rest and during exercise in humans, how these values change with training, and the systemic hemodynamic adaptations that support them. We highlight the very high muscle blood flow responses to exercise discovered in the 1980s. We also discuss the vasodilating factors in the contracting muscles responsible for these very high flows. Finally, the competition between demand for blood flow by contracting muscles and maximum systemic cardiac output is discussed as a potential challenge to blood pressure regulation during heavy large muscle mass or whole body exercise in humans. At this time, no one dominant dilator mechanism accounts for exercise hyperemia. Additionally, complex interactions between the sympathetic nervous system and the microcirculation facilitate high levels of systemic oxygen extraction and permit just enough sympathetic control of blood flow to contracting muscles to regulate blood pressure during large muscle mass exercise in humans.

Pulse transit time measured by photoplethysmography improves the accuracy of heart rate as a surrogate measure of cardiac output, stroke volume and oxygen uptake in response to graded exercise

Heart rate (HR) is a valuable and widespread measure for physical training programs, although its description of conditioning is limited to the cardiac response to exercise. More comprehensive measures of exercise adaptation include cardiac output (Q̇), stroke volume (SV) and oxygen uptake (V̇O2), but these physiological parameters can be measured only with cumbersome equipment installed in clinical settings. In this work, we explore the ability of pulse transit time (PTT) to represent a valuable pairing with HR for indirectly estimating Q̇, SV and V̇O2 non-invasively. PTT was measured as the time interval between the peak of the electrocardiographic (ECG) R-wave and the onset of the photoplethysmography (PPG) waveform at the periphery (i.e. fingertip) with a portable sensor. Fifteen healthy young subjects underwent a graded incremental cycling protocol after which HR and PTT were correlated with Q̇, SV and V̇O2 using linear mixed models. The addition of PTT significantly improved the modeling of Q̇, SV and V̇O2 at the individual level ([Formula: see text] for SV, 0.548 for Q̇, and 0.771 for V̇O2) compared to predictive models based solely on HR ([Formula: see text] for SV, 0.503 for Q̇, and 0.745 for V̇O2). While challenges in sensitivity and artifact rejection exist, combining PTT with HR holds potential for development of novel wearable sensors that provide exercise assessment largely superior to HR monitors.

The relationship between workloads, physical performance, injury and illness in adolescent male football players

BACKGROUND

The expectation that training enhances performance is well explored in professional sport. However, the additional challenges of physical and cognitive maturation may require careful consideration when determining workloads to enhance performance in adolescents.

OBJECTIVE

The objective of this study was to determine the state of knowledge on the relationship between workloads, physical performance, injury and/or illness in adolescent male football players.

METHODS

A systematic review of workloads, physical performance, injury and illness in male adolescent football players was conducted. Studies for this review were identified through a systematic search of six electronic databases (Academic Search Complete, CINAHL, PsycINFO, PubMed, SPORTDiscus, and Web of Science). For the purpose of this review, load was defined as the cumulative amount of stress placed on an individual from multiple training sessions and games over a period of time, expressed in terms of either the external workloads performed (e.g., resistance lifted, kilometres run) or the internal response (e.g., heart rate, rating of perceived exertion) to that workload.

RESULTS

A total of 2,081 studies were initially retrieved from the six databases, of which 892 were duplicates. After screening the titles, abstracts and full texts, we identified 23 articles meeting our criteria around adolescent football players, workloads, physical performance, injury and/or illness. Seventeen articles addressed the relationship between load and physical performance, four articles addressed the relationship between load and injury and two articles addressed both. A wide range of training modalities were employed to improve the physical performance of adolescent football players, with strength training, high-intensity interval training, dribbling and small-sided games training, and a combination of these modalities in addition to normal football training, resulting in improved performances on a wide range of physiological and skill assessments. Furthermore, there was some (limited) evidence that higher workloads may be associated with the development of better physical qualities, with one study demonstrating enhanced submaximal interval shuttle run performance with each additional hour of training or game play. Of the few studies examining negative consequences associated with workloads, increases in training load led to increases in injury rates, while longer training duration was associated with a greater incidence of illness.

CONCLUSION

The combined capacity for adolescent males to grow, train and improve physical performance highlights and underscores an exciting responsiveness to training in the football environment. However, the capacity to train has some established barriers for adolescents experiencing high workloads, which could also result in negative consequences. Additional research on stage-appropriate training for adolescent male footballers is required in order to address the knowledge gaps and enhance safe and efficient training practices.

Personalized preventive medicine: genetics and the response to regular exercise in preventive interventions

Regular exercise and a physically active lifestyle have favorable effects on health. Several issues related to this theme are addressed in this report. A comment on the requirements of personalized exercise medicine and in-depth biological profiling along with the opportunities that they offer is presented. This is followed by a brief overview of the evidence for the contributions of genetic differences to the ability to benefit from regular exercise. Subsequently, studies showing that mutations in TP53 influence exercise capacity in mice and humans are succinctly described. The evidence for effects of exercise on endothelial function in health and disease also is covered. Finally, changes in cardiac and skeletal muscle in response to exercise and their implications for patients with cardiac disease are summarized. Innovative research strategies are needed to define the molecular mechanisms involved in adaptation to exercise and to translate them into useful clinical and public health applications.

Maximal oxygen consumption in healthy humans: theories and facts

This article reviews the concept of maximal oxygen consumption ([Formula: see text]) from the perspective of multifactorial models of [Formula: see text] limitation. First, I discuss procedural aspects of [Formula: see text] measurement: the implications of ramp protocols are analysed within the theoretical work of Morton. Then I analyse the descriptive physiology of [Formula: see text], evidencing the path that led to the view of monofactorial cardiovascular or muscular [Formula: see text] limitation. Multifactorial models, generated by the theoretical work of di Prampero and Wagner around the oxygen conductance equation, represented a radical change of perspective. These models are presented in detail and criticized with respect to the ensuing experimental work. A synthesis between them is proposed, demonstrating how much these models coincide and converge on the same conclusions. Finally, I discuss the cases of hypoxia and bed rest, the former as an example of the pervasive effects of the shape of the oxygen equilibrium curve, the latter as a neat example of adaptive changes concerning the entire respiratory system. The conclusion is that the concept of cardiovascular [Formula: see text] limitation is reinforced by multifactorial models, since cardiovascular oxygen transport provides most of the [Formula: see text] limitation, at least in normoxia. However, the same models show that the role of peripheral resistances is significant and cannot be neglected. The role of peripheral factors is greater the smaller is the active muscle mass. In hypoxia, the intervention of lung resistances as limiting factors restricts the role played by cardiovascular and peripheral factors.

Genomics and genetics in the biology of adaptation to exercise

This article is devoted to the role of genetic variation and gene-exercise interactions in the biology of adaptation to exercise. There is evidence from genetic epidemiology research that DNA sequence differences contribute to human variation in physical activity level, cardiorespiratory fitness in the untrained state, cardiovascular and metabolic response to acute exercise, and responsiveness to regular exercise. Methodological and technological advances have made it possible to undertake the molecular dissection of the genetic component of complex, multifactorial traits, such as those of interest to exercise biology, in terms of tissue expression profile, genes, and allelic variants. The evidence from animal models and human studies is considered. Data on candidate genes, genome-wide linkage results, genome-wide association findings, expression arrays, and combinations of these approaches are reviewed. Combining transcriptomic and genomic technologies has been shown to be more powerful as evidenced by the development of a recent molecular predictor of the ability to increase VO2max with exercise training. For exercise as a behavior and physiological fitness as a state to be major players in public health policies will require that the role of human individuality and the influence of DNA sequence differences be understood. Likewise, progress in the use of exercise in therapeutic medicine will depend to a large extent on our ability to identify the favorable responders for given physiological properties to a given exercise regimen.

Fine mapping of a QTL on chromosome 13 for submaximal exercise capacity training response: the HERITAGE Family Study

Although regular exercise improves submaximal aerobic capacity, there is large variability in its response to exercise training. While this variation is thought to be partly due to genetic differences, relatively little is known about the causal genes. Submaximal aerobic capacity traits in the current report include the responses of oxygen consumption (ΔVO(2)60), power output (ΔWORK60), and cardiac output (ΔQ60) at 60% of VO2max to a standardized 20-week endurance exercise training program. Genome-wide linkage analysis in 475 HERITAGE Family Study Caucasians identified a locus on chromosome 13q for ΔVO(2)60 (LOD = 3.11). Follow-up fine mapping involved a dense marker panel of over 1,800 single-nucleotide polymorphisms (SNPs) in a 7.9-Mb region (21.1-29.1 Mb from p-terminus). Single-SNP analyses found 14 SNPs moderately associated with both ΔVO(2)60 at P ≤ 0.005 and the correlated traits of ΔWORK60 and ΔQ60 at P < 0.05. Haplotype analyses provided several strong signals (P < 1.0 × 10(-5)) for ΔVO(2)60. Overall, association analyses narrowed the target region and included potential biological candidate genes (MIPEP and SGCG). Consistent with maximal heritability estimates of 23%, up to 20% of the phenotypic variance in ΔVO(2)60 was accounted for by these SNPs. These results implicate candidate genes on chromosome 13q12 for the ability to improve submaximal exercise capacity in response to regular exercise. Submaximal exercise at 60% of maximal capacity is an exercise intensity that falls well within the range recommended in the Physical Activity Guidelines for Americans and thus has potential public health relevance.

KIF5B gene sequence variation and response of cardiac stroke volume to regular exercise

A genome-wide linkage scan for endurance training-induced changes in stroke volume detected a quantitative trait locus on chromosome 10p11 in white families of the HERITAGE Family Study. Dense microsatellite mapping narrowed down the linkage region to a 7 Mb area containing 16 known and 14 predicted genes. Association analyses with 90 single nucleotide polymorphisms (SNPs) provided suggestive evidence (P values from 0.03 to 0.06) for association in the kinesin heavy chain (KIF5B) gene locus in the whole cohort. The associations at the KIF5B locus were stronger (P values from 0.001 to 0.008) when the analyses were performed on linkage-informative families only (family-specific logarithm of the odds ratio scores >0.025 at peak linkage location). Resequencing the coding and regulatory regions of KIF5B revealed no new exonic SNPs. However, the putative promoter region was particularly polymorphic, containing eight SNPs with at least 5% minor allele frequency within 1850 bp upstream of the start codon. Functional analyses using promoter haplotype reporter constructs led to the identification of sequence variants that had significant effects on KIF5B promoter activity. Analogous inhibition and overexpression experiments showed that changes in KIF5B expression alter mitochondrial localization and biogenesis in a manner that could affect the ability of the heart to adjust to regular exercise. Our data suggest that KIF5B is a strong candidate gene for the response of stroke volume to regular exercise. Furthermore, training-induced changes in submaximal exercise stroke volume may be due to mitochondrial function and variation in KIF5B expression as determined by functional SNPs in its promoter.

Genes, exercise, growth, and the sedentary, obese child

It is still not possible to provide an evidence-based answer to the question of whether regular exercise is essential for normal growth. It is also unclear whether very low levels of exercise result in growth deficits. Regular exposure to exercise is characterized by heterogeneity in responsiveness, with most individuals experiencing improvements in fitness traits but a significant proportion showing only very minor gains. Whether a sedentary mode of life during the growing years results in a permanent deficit in cardiorespiratory fitness or a diminished ability to respond favorably to regular exercise later in life remains to be investigated. Although several genes have been associated with fitness levels or response to regular exercise, the quality of the evidence is weak mainly because studies are statistically underpowered. The special case of the obese, sedentary child is discussed, and the importance of the "energy gap" in the excess weight gain during growth is highlighted. Obese, sedentary children have high blood pressure, dyslipidemia, elevated glycemia and type 2 diabetes, hepatic steatosis, respiratory problems, orthopedic complications, and other health disorders more frequently than normal weight, physically active children. The role of genetic differences in the inclination to be sedentary or physically active is reviewed. An understanding of the true role of genetic differences and regular exercise on the growth of children will require more elaborate paradigms incorporating not only DNA sequence variants and exercise exposure but also information on nutrition, programming, and epigenetic events during fetal life and early postnatal years.

Association between HMOX-1 genotype and cardiac function during exercise

The human gene for heme oxygenase-1 (HMOX-1) plays an important role in the regulation of cardiovascular function and its adaptive response to a variety of stressors. The purpose of this study was to examine the possible association between HMOX-1 genotypes (for –1135A/G, –413A/T, and rs5755720 polymorphisms) and cardiac structural and functional parameters at rest and during submaximal cycle-ergometer exercise (50, 100, and 150 W) in a pre-training state (baseline) and after endurance training (18 weeks, 95%~105% individual ventilatory threshold). The study population consisted of 102 Chinese young males (non-athletes) of Han origin. For the –1135A/G polymorphism, we found a significant genotype effect (p < 0.05) in cardiac output (Q) corrected for body surface area (BSA; Q·BSA–1) at 50 W and stroke volume (SV) corrected for BSA (SV·BSA–1) at 100 W. For the –413A/T polymorphism, we found a significant genotype effect (p < 0.05) in ejection fraction (EF) at 100 W. For the rs5755720 polymorphism, we found a significant genotype effect (p < 0.01 or p < 0.05) in most variables (Q·BSA–1 across all workloads, SV·BSA–1 at 100 W, and EF at 50 and 100 W). Briefly, rs5755720 individuals with a CC genotype presented overall higher values in the different cardiac variables than their CT and (or) TT counterparts. In summary, although more research is needed with diseased populations and other ethnic groups, we found preliminary evidence of an association between cardiac response to submaximal exercise and HMOX-1 genotype. The present preliminary findings could provide insights to future studies searching for cardioprotective genotypes.

Effects of Gender on Physiological Responses during Submaximal Exercise and Recovery

PURPOSE

This investigation was conducted to compare the physiological responses of men and women, both during and following an exercise bout at the same relative submaximal intensity.

METHODS

Ten untrained men (20.7+/-0.5 yr, 178.4+/-2.3 cm, 79.6+/-4.8 kg; mean+/-SE) and 10 untrained women (20.3+/-0.3 yr, 163.8+/-2.2 cm, 59.5+/-2.1 kg) cycled for 30 min at 60-65% of their predetermined peak oxygen uptake. Physiological variables were measured before exercise, at 15 and 30 min of exercise, and at 5 and 15 min postexercise. For each variable of interest, a two-way repeated-measures of analysis was used to assess the main effects of gender and time, along with potential interactive effects.

RESULTS

Our data revealed that for many variables including HR, relative HR (% peak value), mean arterial pressure, and rectal temperature, men and women responded similarly both during exercise and throughout the recovery period. In contrast, significant (P<or=0.05) gender-related differences were noted for RER, plasma lactate, systolic blood pressure, and plasma volume shifts. In each of those variables, values displayed by men during exercise were significantly greater than those observed among women. However, with the exception of plasma lactate, those gender-related differences did not persist into recovery.

CONCLUSION

During exercise of the same relative submaximal intensity, some physiological parameters responded likewise in young men and young women, whereas others did not. Among those variables that demonstrated significant gender-related differences, all but one (plasma lactate) were obscured within 5 min of postexercise recovery.

DNA sequence variation in the promoter region of the VEGF gene impacts VEGF gene expression and maximal oxygen consumption

In its role as an endothelial cell proliferation and migration factor, vascular endothelial growth factor (VEGF) can affect peripheral circulation and therefore impact maximal oxygen consumption (Vo2 max). Because of the role of VEGF, and because variation in the VEGF gene has the ability to alter VEGF gene expression and VEGF protein level, we hypothesized that VEGF gene polymorphisms are related to VEGF gene expression in human myoblasts and Vo2 max before and after aerobic exercise training. We analyzed the effects of the VEGF -2578/-1154/-634 promoter region haplotype on VEGF gene expression by using a luciferase reporter assay in cultured human myoblasts and found that the AAG and CGC haplotypes resulted in significantly higher hypoxia-stimulated VEGF gene expression than the AGG and CGG haplotypes. Consistent with these results, we found that individuals with at least one copy of the AAG or CGC haplotype had higher Vo2 max before and after aerobic exercise training than did subjects with only the AGG and/or CGG haplotype. In conclusion, we found that VEGF -2578/-1154/-634 haplotype impacts VEGF gene expression in human myoblasts and is associated with Vo2 max. These results have potential implications for aerobic exercise training and may prove relevant in the study of pathological conditions that can be affected by angiogenesis, such as coronary artery disease and peripheral artery disease.

Quantitative trait loci for maximal exercise capacity phenotypes and their responses to training in the HERITAGE Family Study

The purpose of this study was to identify regions of the human genome linked to maximal oxygen uptake (V̇o2 max) and maximal power output (MPO), and their response to a standardized 20-wk endurance-training program in sedentary black and white subjects. A total of 509 polymorphic markers covering the 22 autosomes were used in the genome-wide linkage scan. Baseline phenotypes were adjusted for age, sex, and body mass, whereas the training responses were adjusted for age, sex, and the baseline values. Regression-based single- and multipoint linkage analyses were used. In the sedentary state, a total of 351 and 102 sibling pairs were available for whites and blacks, respectively, and 329 and 90 sibling pairs, respectively, for the training response phenotypes. Baseline V̇o2 maxshowed promising linkage ( P < 0.0023) with 11p15.1 (whites), and suggestive evidence of linkage (0.01 > P > 0.0023) was found on 1p31, 7q32, and 7q36 (blacks). Baseline MPO exhibited promising linkage on 10q23 and suggestive evidence of linkage on 13q33 and 18q11-q12 (whites). V̇o2 maxtraining response yielded promising linkages with markers on 1p31 (blacks) and suggestive on 4q27, 7q34, and 13q12 (whites) and on 16q22 and 20q13.1 (blacks). Training-induced changes in MPO showed promising linkages on 5q23 (whites) and suggestive on 1q21, 4p15.1, and 4p13 (whites) and on 1q22 and 13q11 (blacks). In conclusion, the strongest evidence of linkage was found on chromosomal regions 11p15 and 10q23 for V̇o2 maxand MPO in the sedentary state and on chromosomes 1p31 and 5q23 for their responsiveness to training. These chromosomal regions harbor several candidate genes that deserve further investigation.

Effect of habitual running on human Achilles tendon load-deformation properties and cross-sectional area

Whether the cross-sectional area (CSA) and mechanical properties of the human Achilles tendon change in response to habitual exercise remains largely unexplored. The present study evaluated the CSA and contraction-induced displacement of the aponeurosis-tendon complex of the triceps surae in 11 untrained subjects before (tests 1 and 2) and after (test 3) approximately 9 mo of regular running ( approximately 78 training sessions). Displacement of the tendon-aponeurosis complex obtained by ultrasonography; electromyography of the gastrocnemius, soleus, and dorsiflexor muscles; and joint angular rotation were recorded during graded isometric plantarflexion ramps. Tendon CSA and moment arm were measured by using MRI, and tendon force was calculated from joint moments and tendon moment arm. A treadmill test was used to determine submaximal oxygen consumption (Vo2) at a given speed and maximal Vo2. The total running duration was approximately 43 h, distributed over 34 wk. Maximal Vo2 increased 8.6% (P < 0.01), and submaximal Vo2 decreased 6.2% (P < 0.05). Tendon-aponeurosis displacement during maximal voluntary contraction was unchanged (tests 1-3, 5.2 +/- 0.6, 5.2 +/- 0.5, and 5.3 +/- 0.4 mm, respectively) and yielded a structural stiffness of 365 +/- 50, 358 +/- 40, and 384 +/- 52 N/mm for tests 1-3, respectively (P > 0.05). Tendon CSA also remained unchanged (tests 1-3, 34.2 +/- 2.2, 33.9 +/- 2.2, and 33.8 +/- 2.1 mm2, respectively). In conclusion, a total training stimulus of approximately 9 mo of running in previously untrained subjects was adequate to induce significant cardiovascular improvements, although it did not result in any changes in the mechanical properties of the triceps surea tendon-aponeurosis complex or in the dimensions of Achilles tendon.

Titin is a candidate gene for stroke volume response to endurance training: the HERITAGE Family Study

A genome-wide linkage scan for endurance training-induced changes in submaximal exercise stroke volume (DeltaSV50) in the HERITAGE Family Study revealed two chromosomal regions (2q31-q32 and 10p11.2) with at least suggestive evidence of linkage among white families. Here we report a further characterization of the quantitative trait locus (QTL) in chromosome 2q31 and provide evidence that titin (TTN) is likely a candidate gene involved. The original linkage was detected with two markers (D2S335 and D2S1391), and the QTL covered approximately 25 million base pairs (Mb). We added 12 microsatellite markers resulting in an average marker density of one marker per 2.3 Mb. The evidence of linkage increased from P = 0.006 to P = 0.0002 and 0.00002 in the multi- and single-point analyses, respectively. The strongest evidence of linkage was seen with two markers in and near the TTN gene. Transmission/disequilibrium test (TDT) with the same marker set provided evidence for association with one of the TTN markers (D2S385; P = 0.004). TTN is a major contributor to the elasticity of cardiomyocytes and a key regulator of the Frank-Starling mechanism. Since TTN is the largest gene in the human genome, the challenge is to identify the DNA sequence variants contributing to the interindividual differences in cardiac adaptation to endurance training.

The effects of interval training on oxygen pulse and performance in supra-threshold runs

The aim of this study was to examine (i) the effects of a severe interval training period on oxygen pulse kinetics (O2-p, the ratio between VO2 and heart rate), and (ii) to study the consequences of these effects on the variation of performance (time to exhaustion) during severe runs. Seven athletes were tested before and after an eight-weeks period of a specific intermittent training at v Delta 50, i.e., the intermediate velocity between the lactate threshold (vLT) and the velocity associated with VO2max (vVO2max ). During the test sessions, athletes performed an incremental test and an all-out test at the pretraining v Delta 50. After the training period they also completed an additional all-out test at the posttraining v Delta 50 (v Delta 50bis). Results showed that after training there was i) an increase in the O2-p maximal value during the incremental test (22.7 +/- 1.5 mlO2.b-1 vs. 20.6 +/- 1.5 mlO2.b-1; p < 0.04), ii) a decrease in the time to reach the O2-p steady state (TRO2-p ) at the same absolute v Delta 50 (33 +/- 7 s vs. 60 +/- 27 s; p < 0.04) and iii) an increase in the O2-p steady state duration (TSSO2-p) at the same absolute v Delta 50 (552 +/- 201 s vs. 407 +/- 106 s; p < 0.04). However, there was no relationship between the improvement of these two O 2 -p kinetics parameters (TRO2-p and TSS O2-p) and those of the performance. This study found that after an individualised interval-training program conducted at the same absolute velocity, the O2-p kinetics reached a steady state quicker and for a longer duration than before training. This is however not related with the improvement of performance.

Cardiovascular responses to endurance training in children: effect of gender

BACKGROUND

The aim of the present study was to determine in healthy children the effect of a well-controlled endurance training programme on cardiac function at maximal exercise and to define whether gender affects the training-induced cardiovascular response. The contribution of factors potentially involved in those adaptations such as cardiac dimensions and diastolic and systolic function was also investigated.

METHODS

Thirty-five l0-11-year-old children took part in this study: 19 children (10 girls and nine boys) were assigned to participate in a 13-week endurance training programme (3 x 1 h week-1, intensity: > 80% HR max), and 16 (seven girls and nine boys) served as a control group. A resting echocardiographic evaluation and a maximal upright cycle test, including measurement of stroke volume (SV), cardiac output (Q) and blood pressure, were performed in all children before and after the study period.

RESULTS

The training programme led to a rise in maximal O2 uptake (VO2max), brought about however, only by an increase in SVmax in both genders. Moreover, the boys increased their VO2max to a greater extent than the girls (boys: +15%; girls: +8%) only because of a higher SVmax improvement (boys: +15%; girls: +11%). No alterations were noticed in the SV pattern from rest to maximal exercise, indicating that the increase in SVrest was a key factor in the improvement of SVmax and thus VO2max. Regarding resting echocardiographic data, an increase in the left ventricular end-diastolic diameter, concomitant with an improvement in diastolic function, was observed after training and constituted an essential element in the rise in VO2max after training in these children. Moreover, during maximal exercise, a decrease in systemic vascular resistances, probably indicating peripheral cardiovascular adaptive changes, might also play an important role in the increase in VO2max.

CONCLUSION

Whatever gender, aerobic training increases VO2max in children, mediated by an improvement in SVmax only. Similar mechanisms, including loading conditions and cardiac morphology, seem to be involved in both genders in order to explain such an improvement.

The effects of aging and activity on muscle blood flow

BACKGROUND

Our purpose was to determine if aging had an influence on muscle blood flow independent of habitual physical activity levels.

METHODS

Blood flow was measured in the femoral artery by Doppler ultrasound after cuff occlusion of 10 minutes. Active and inactive older subjects (73 +/- 7 years) were compared to active and inactive young subjects (26 +/- 6 years).

RESULTS

Peak blood flow capacity when normalized to lean muscle mass was related to activity level (p < 0.001), but not to age. Specifically, the young active group had higher peak blood flows than the young inactive (p = 0.031) or older inactive (p = 0.005) groups. Resting blood flow and conductance were not significantly different between groups. Mean arterial pressure was significantly higher in the older compared to young group (p = 0.002). Conductance was related to both activity (p = 0.002) and age (p = 0.003). A prolonged time for blood flow to recover was found in the older compared to the young group (p = 0.038) independent of activity status.

CONCLUSIONS

The prolonged recovery time in the older subjects may suggest a reduced vascular reactivity associated with increased cardiovascular disease risk. Peak blood flow capacity is maintained in older subjects by physical activity. In summary, maximal flow capacity and prolonged recovery of blood flow are influenced by different mechanisms in young and older active and inactive subjects.

Major gene effects on exercise ventilatory threshold: the HERITAGE Family Study

This study investigates whether there are major gene effects on oxygen uptake at the ventilatory threshold (VO(2VT)) and the VO(2VT) maximal oxygen uptake (VT%VO(2 max)), at baseline and in response to 20 wk of exercise training by using data on 336 whites and 160 blacks. Segregation analysis was performed on the residuals of VO(2VT) and VT%VO(2 max). In whites, there was strong evidence of a major gene, with 3 and 2% of the sample in the upper distribution, that accounted for 52 and 43% of the variance in baseline VO(2VT) and VT%VO(2 max), respectively. There were no genotype-specific covariate effects (sex, age, weight, fat mass, and fat-free mass). The segregation results were inconclusive for the training response in whites, and for the baseline and training response in blacks, probably due to insufficient power because of reduced sample sizes or smaller gene effect or both. The strength of the genetic evidence for VO(2VT) and VT%VO(2 max) suggests that these traits should be further investigated for potential relations with specific candidate genes, if they can be identified, and explored through a genome-wide scan.

Genome-wide linkage scan for exercise stroke volume and cardiac output in the HERITAGE Family Study

A genome-wide linkage scan was performed for genes affecting submaximal exercise cardiac output (Q) and stroke volume (SV) in the sedentary state and their responses to a standardized 20-wk endurance training program. A total of 509 polymorphic markers were used, and 328 pairs of siblings from 99 white nuclear families and 102 sibling pairs from 105 black family units were available. Q and SV were measured in relative steady state during exercise at 50 W (Q50 and SV50, respectively). Baseline phenotypes were adjusted for age, sex, and body surface area (BSA), and the training responses (post-training - baseline, Delta) were adjusted for age, sex, baseline BSA, and baseline value of the phenotype. Three analytical strategies were used: a multipoint variance components linkage analysis using all the family data, and regression-based single- and multipoint linkage analyses using pairs of siblings. In whites, baseline SV50 and DeltaSV50 showed promising linkages (P < 0.0023) with markers on chromosomes 14q31.1 and 10p11.2, respectively. Suggestive evidence of linkage (0.01 > P > 0.0023) for DeltaSV50 and Delta Q50 was detected on chromosome 2q31.1 and for baseline SV50 and Q50 on chromosome 9q32-q33. In blacks, markers on 18q11.2 showed promising linkages with baseline Q50. Suggestive evidence of linkage was found in three regions for baseline SV50 (1p21.3, 3q13.3, 12q13.2) and one for baseline SV50 and Q50 (10p14). All these chromosomal regions include several potential candidate genes and therefore warrant further studies in the HERITAGE cohort and other studies.

G protein beta 3 polymorphism and hemodynamic and body composition phenotypes in the HERITAGE Family Study

A C825T polymorphism of the G protein beta3 (GNB3) gene has been reported to be associated with hypertension and obesity. We analyzed the associations between the GNB3 C825T polymorphism and hemodynamic and body composition phenotypes in the sedentary state and their responses to endurance training in mainly normotensive white (n = 473) and black (n = 255) men and women. Blood pressure (BP) and heart rate (HR) were measured at rest and during submaximal exercise at constant power output (50 W), and stroke volume and cardiac output were obtained during exercise. Body composition was assessed with underwater weighing. Baseline systolic BP (SBP) at 50 W was slightly higher in the white CC homozygotes (P = 0.036), whereas in blacks the CC genotype was associated with a lower resting HR (P = 0.012). In blacks, the CC homozygotes showed a greater training-induced reduction in HR at 50 W (P = 0.013) and a similar trend was observed also in whites (P = 0.053). Black women carrying the CC genotype showed significantly greater reductions in resting SBP and diastolic BP (DBP) than the TT homozygotes, whereas in black men the changes in resting BP were similar across the genotypes (P < 0.05 for sex-by-GNB3 interactions). The GNB3 genotype was not associated with baseline body composition in blacks or whites. In blacks, the TT genotype was associated with a greater training-induced decrease in fat mass (P = 0.012) and percent body fat (P = 0.006). These data suggest that DNA sequence variation in the GNB3 locus is not a major modifier of endurance training-induced changes in hemodynamic and body composition phenotypes in healthy but previously sedentary subjects. The GNB3 genotype may play a minor role in HR and body fatness regulation in blacks and in responsiveness of resting BP to endurance training in black women.