VO2max: what do we know, and what do we still need to know?

Determining V̇O2max in competitive swimmers: Comparing the validity and reliability of cycling, arm cranking, ergometer swimming, and tethered swimming

OBJECTIVES

This study aims to identify the optimal method for determining V̇O2max in competitive swimmers in terms of validity and test-retest reliability.

DESIGN

Controlled experiment.

METHODS

Twenty competitive swimmers performed four maximal incremental exercise tests: cycling, arm cranking, ergometer swimming, and tethered swimming. Gas analysis was conducted to estimate V̇O2max. Validity was assessed in terms of the amount of variance of the performance on a 1500-m time trial explained by the estimated V̇O2max . Test-retest reliability was evaluated using the intraclass correlation coefficient (ICC).

RESULTS

V̇O2max obtained from tethered swimming, ergometer swimming, and cycling explained a similar amount of variance of the 1500-m performance (R2 = 0.64, 0.64 and 0.65, respectively). However, ergometer swimming yielded significantly lower V̇O2max estimates (40.54 ± 6.55 ml/kg/min) than tethered swimming (54.40 ± 6.21 ml/kg/min) and cycling (54.39 ± 5.63 ml/kg/min). Arm cranking resulted in both a lower explained variance (R2 = 0.41) and a significantly lower V̇O2max (43.14 ± 7.81 ml/kg/min). Tethered swimming showed good reliability (ICC = 0.81).

CONCLUSIONS

Bicycle and tethered swimming tests demonstrated high validity with comparable V̇O2max estimates, explaining a large proportion of differences in endurance performance. Choosing between these two methods involves a trade-off between a higher practical applicability and reliability of the bicycle test and the more sport-specific nature of the tethered swimming test.

Wagner diagram for modeling O2pathway-calculation and graphical display by the Helsinki O2Pathway Tool

Objective.Maximal O2uptake (V˙O2max) reflects the individual's maximal rate of O2transport and utilization through the integrated whole-body pathway composed of the lungs, heart, blood, circulation, and metabolically active tissues. As such,V˙O2maxis strongly associated with physical capacity as well as overall health and thus acts as one predictor of physical performance and as a vital sign in determination of status and progress of numerous clinical conditions. Quantifying the contribution of single parts of the multistep O2pathway toV˙O2maxprovides mechanistic insights into exercise (in)tolerance and into therapy-, training-, or disuse-induced adaptations at individual or group levels. We developed a desktop application (Helsinki O2Pathway Tool-HO2PT) to model numerical and graphical display of the O2pathway based on the 'Wagner diagram' originally formulated by Peter D. Wagner and his colleagues.Approach.The HO2PT was developed and programmed in Python to integrate the Fick principle and Fick's law of diffusion into a computational system to import, calculate, graphically display, and export variables of the Wagner diagram.Main results.The HO2PT models O2pathway both numerically and graphically according to the Wagner diagram and pertains to conditions under which the mitochondrial oxidative capacity of metabolically active tissues exceeds the capacity of the O2transport system to deliver O2to the mitochondria. The tool is based on the Python open source code and libraries and freely and publicly available online for Windows, macOS, and Linux operating systems.Significance.The HO2PT offers a novel functional and demonstrative platform for those interested in examiningV˙O2maxand its determinants by using the Wagner diagram. It will improve access to and usability of Wagner's and his colleagues' integrated physiological model and thereby benefit users across the wide spectrum of contexts such as scientific research, education, exercise testing, sports coaching, and clinical medicine.

Impaired longitudinal systolic-diastolic coupling and cardiac response to exercise in patients with hypertrophic cardiomyopathy

BACKGROUND

In patients with hypertrophic cardiomyopathy (HCM), impaired augmentation of stroke volume and diastolic dysfunction contribute to exercise intolerance. Systolic-diastolic (S-D) coupling characterizes how systolic contraction of the left ventricle (LV) primes efficient elastic recoil during early diastole. Impaired S-D coupling may contribute to the impaired cardiac response to exercise in patients with HCM.

METHODS

Patients with HCM (n = 25, age = 47 ± 9 years) and healthy adults (n = 115, age = 49 ± 10 years) underwent a cardiopulmonary exercise testing (CPET) and echocardiogram. S-D coupling was defined as the ratio of LV longitudinal excursion of the mitral annulus during early diastole (EDexc) and systole (Sexc) and compared between groups. Peak oxygen uptake (peak V̇O2) (Douglas bags), cardiac index (C2H2 rebreathe), and stroke volume index (SVi) were assessed during CPET. Linear regression was performed between S-D coupling and peak V̇O2, peak cardiac index, and peak SVi.

RESULTS

S-D coupling was lower in HCM (Controls: 0.63 ± 0.08, HCM: 0.56 ± 0.10, p < 0.001). Peak V̇O2 and stroke volume reserve were lower in patients with HCM (Peak VO2 Controls: 28.5 ± 5.5, HCM: 23.7 ± 7.2 mL/kg/min, p < 0.001, SV reserve: Controls 39 ± 16, HCM 30 ± 18 mL, p = 0.008). In patients with HCM, S-D coupling was associated with peak V̇O2 (r = 0.47, p = 0.018), peak cardiac index (r = 0.60, p = 0.002), and peak SVi (r = 0.63, p < 0.001).

CONCLUSION

Systolic-diastolic coupling was impaired in patients with HCM and was associated with fitness and the cardiac response to exercise. Inefficient S-D coupling may link insufficient stroke volume generation, diastolic dysfunction, and exercise intolerance in HCM.

Changes in red blood cell parameters during incremental exercise in highly trained athletes of different sport specializations

Background

During physical exercise, the level of hematological parameters change depending on the intensity and duration of exercise and the individual's physical fitness. Research results, based on samples taken before and after exercise, suggest that hematological parameters increase during incremental exercise. However, there is no data confirming this beyond any doubt. This study examined how red blood cell (RBC) parameters change during the same standard physical exertion in athletes representing different physiological training profiles determined by sport discipline.

Methods

The study included 39 highly trained male members of national teams: 13 futsal players, 12 sprinters, and 14 triathletes. We used multiple blood sampling to determine RBC, hemoglobin (Hb), hematocrit value (Hct), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), and red blood cell distribution width (RDW) before, during (every 3 min), and after (5, 10, 15, 20, and 30 min) an incremental treadmill exercise test until exhaustion.

Results

There were no significant exercise-induced differences in RBC parameters between athletic groups. No significant changes were recorded in RBC parameters during the low-intensity phase of exercise. RBC, Hb, and Hct increased significantly during incremental physical exercise, and rapidly returned to resting values upon test termination.

Conclusions

The general pattern of exercise-induced changes in RBC parameters is universal regardless of the athlete's physiological profile. The changes in RBC parameters are proportional to the intensity of exercise during the progressive test. The increase in hemoglobin concentration associated with the intensity of exercise is most likely an adaptation to the greater demand of tissues, mainly skeletal muscles, for oxygen.

The cardiovascular changes underlying a low cardiac output with exercise in patients with type 2 diabetes mellitus

The significant morbidity and premature mortality of type 2 diabetes mellitus (T2DM) is largely associated with its cardiovascular consequences. Focus has long been on the arterial atheromatosis of DM giving rise to early stroke and myocardial infarctions, whereas less attention has been given to its non-ischemic cardiovascular consequences. Irrespective of ischemic changes, T2DM is associated with heart failure (HF) most commonly with preserved ejection fraction (HFpEF). Largely due to increasing population ages, hypertension, obesity and T2DM, HFpEF is becoming the most prevalent form of heart failure. Unfortunately, randomized controlled trials of HFpEF have largely been futile, and it now seems logical to address the important different phenotypes of HFpEF to understand their underlying pathophysiology. In the early phases, HFpEF is associated with a significantly impaired ability to increase cardiac output with exercise. The lowered cardiac output with exercise results from both cardiac and peripheral causes. T2DM is associated with left ventricular (LV) diastolic dysfunction based on LV hypertrophy with myocardial disperse fibrosis and significantly impaired ability for myocardial blood flow increments with exercise. T2DM is also associated with impaired ability for skeletal muscle vasodilation during exercise, and as is the case in the myocardium, such changes may be related to vascular rarefaction. The present review discusses the underlying phenotypical changes of the heart and peripheral vascular system and their importance for an adequate increase in cardiac output. Since many of the described cardiovascular changes with T2DM must be considered difficult to change if fully developed, it is suggested that patients with T2DM are early evaluated with respect to their cardiovascular compromise.

Cardiopulmonary Exercise Testing Interpretation in Athletes: What the Cardiologist Should Know

The noninvasive assessment of oxygen consumption, carbon dioxide production, and ventilation during a cardiopulmonary exercise test (CPET) provides insight into the cardiovascular, pulmonary, and metabolic system's ability to respond to exercise. Exercise physiology has been shown to be distinct for competitive athletes and highly active persons (CAHAPs), thus creating more nuanced interpretations of CPET parameters. CPET in CAHAP is an important test that can be used for both diagnosis (provoking symptoms during a truly maximal test) and performance.

Overdot and overline annotation must be understood to accurately interpret V.O2MAX physiology with the Fick formula

Few formulas have been used in exercise physiology as extensively as the Fick formula, which calculates the rate of oxygen consumption (i.e., V.O2) as the product of cardiac output (Q.) and the difference in oxygen content in arterial and mixed venous blood (Δav ¯ O2). Unfortunately, the physiology of maximum V.O2 (V.O2MAX) is often misinterpreted due to a lack of appreciation for the limitations represented by the oft-ignored superscript annotations in the Fick formula. The purpose of this perspective is to explain the meaning of the superscript annotations and highlight how such annotations influence proper interpretation of V.O2MAX physiology with the Fick formula. First, we explain the significance of the overdots above V.O2 and Q., which indicate a measure per unit of time. As we will show, the presence of an overdot above Q. and lack of one above Δav ¯ O2 denotes they are different types of ratios and should be interpreted in the context of one another-not in contrast to each other as is commonplace. Second, we discuss the significance of the overline above the "v ¯ " in Δav ¯ O2, which indicates the venous sample is an average of blood that comes from mixed sources. The mixed nature of the venous sample has major implications for interpreting the influence of oxygen diffusion and blood flow heterogeneity on V.O2MAX. Ultimately, we give recommendations and insights for using the Fick formula to calculate V.O2 and interpret V.O2MAX physiology.

Vascular dysfunction and the age-related decline in critical power

Ageing results in lower exercise tolerance, manifested as decreased critical power (CP). We examined whether the age-related decrease in CP occurs independently of changes in muscle mass and whether it is related to impaired vascular function. Ten older (63.1 ± 2.5 years) and 10 younger (24.4 ± 4.0 years) physically active volunteers participated. Physical activity was measured with accelerometry. Leg muscle mass was quantified with dual X-ray absorptiometry. The CP and maximum power during a graded exercise test (PGXT ) of single-leg knee-extension exercise were determined over the course of four visits. During a fifth visit, vascular function of the leg was assessed with passive leg movement (PLM) hyperaemia and leg blood flow and vascular conductance during knee-extension exercise at 10 W, 20 W, slightly below CP (90% CP) and PGXT . Despite not differing in leg lean mass (P = 0.901) and physical activity (e.g., steps per day, P = 0.735), older subjects had ∼30% lower mass-specific CP (old = 3.20 ± 0.94 W kg-1 vs. young = 4.60 ± 0.87 W kg-1 ; P < 0.001). The PLM-induced hyperaemia and leg blood flow and/or conductance were blunted in the old at 20 W, 90% CP and PGXT (P < 0.05). When normalized for leg muscle mass, CP was strongly correlated with PLM-induced hyperaemia (R2  = 0.52; P < 0.001) and vascular conductance during knee-extension exercise at 20 W (R2  = 0.34; P = 0.014) and 90% CP (R2  = 0.39; P = 0.004). In conclusion, the age-related decline in CP is not only an issue of muscle quantity, but also of impaired muscle quality that corresponds to impaired vascular function.

Caffeine intake enhances peak oxygen uptake and performance during high-intensity cycling exercise in moderate hypoxia

PURPOSE

We investigated whether caffeine consumption can enhance peak oxygen uptake ([Formula: see text]) by increasing peak ventilation during an incremental cycling test, and subsequently enhance time to exhaustion (TTE) during high-intensity cycling exercise in moderate normobaric hypoxia.

METHODS

We conducted a double-blind, placebo cross-over design study. Sixteen recreational male endurance athletes (age: 20 ± 2 years, [Formula: see text]: 55.6 ± 3.6 ml/kg/min, peak power output: 318 ± 40 W) underwent an incremental cycling test and a TTE test at 80% [Formula: see text] (derived from the placebo trial) in moderate normobaric hypoxia (fraction of inspired O2: 15.3 ± 0.2% corresponding to a simulated altitude of ~ 2500 m) after consuming either a moderate dose of caffeine (6 mg/kg) or a placebo.

RESULTS

Caffeine consumption resulted in a higher peak ventilation [159 ± 21 vs. 150 ± 26 L/min; P < 0.05; effect size (ES) = 0.31]. [Formula: see text] (3.58 ± 0.44 vs. 3.47 ± 0.47 L/min; P < 0.01; ES = 0.44) and peak power output (308 ± 44 vs. 302 ± 44 W; P = 0.02, ES = 0.14) were higher following caffeine consumption than during the placebo trial. During the TTE test, caffeine consumption enhanced minute ventilation (P = 0.02; ES = 0.28) and extended the TTE (426 ± 74 vs. 358 ± 75 s; P < 0.01, ES = 0.91) compared to the placebo trial. There was a positive correlation between the percent increase of [Formula: see text] following caffeine consumption and the percent increase in TTE (r = 0.49, P < 0.05).

CONCLUSION

Moderate caffeine consumption stimulates breathing and aerobic metabolism, resulting in improved performance during incremental and high-intensity endurance exercises in moderate normobaric hypoxia.

Similar improvements in 5-km performance and maximal oxygen uptake with submaximal and maximal 10-20-30 training in runners, but increase in muscle oxidative phosphorylation occur only with maximal effort training

OBJECTIVE

The aim of the present study was to examine whether 10-20-30 training (consecutive 1-min intervals consisting of 30 s at low-speed, 20 s at moderate-speed, and 10 s at high-speed), performed with submaximal effort during the 10-s high-speed runs, would lead to improved performance as well as increased maximum oxygen uptake (VO2 -max) and muscle oxidative phosphorylation (OXPHOS). In addition, to examine to what extent the effects would compare to 10-20-30 running conducted with maximal effort.

DESIGN

Nineteen males were randomly assigned to 10-20-30 running performed with either submaximal (SUBMAX; n = 11) or maximal (MAX; n = 8) effort, which was conducted three times/week for 6 weeks (intervention; INT). Before and after INT, subjects completed a 5-km running test and a VO2 -max test, and a biopsy was obtained from m. vastus lateralis.

RESULTS

After compared to before INT, SUBMAX and MAX improved (p < 0.05) 5-km performance by 3.0% (20.8 ± 0.4 (means±SE) vs. 21.5 ± 0.4 min) and 2.3% (21.2 ± 0.4 vs. 21.6 ± 0.4 min), respectively, and VO2 -max was ~7% higher (p < 0.01) in both SUBMAX (57.0 ± 1.3 vs. 53.5 ± 1.1 mL/min/kg) and MAX (57.8 ± 1.2 vs. 53.7 ± 0.9 mL/min/kg), with no difference in the changes between groups. In SUBMAX, muscle OXPHOS was unchanged, whereas in MAX, muscle OXPHOS subunits (I-IV) and total OXPHOS (5.5 ± 0.3 vs 4.7 ± 0.3 A.U.) were 9%-29% higher (p < 0.05) after compared to before INT.

CONCLUSION

Conducting 10-20-30 training with a non-maximal effort during the 10-s high-speed runs is as efficient in improving 5-km performance and VO2 -max as maximal effort exercise, whereas increase in muscle OXPHOS occur only when the 10-s high-speed runs are performed with maximal effort.

High or hot-Perspectives on altitude camps and heat-acclimation training as preparation for prolonged stage races

Adaptation to heat stress and hypoxia are relevant for athletes participating in Tour de France or similar cycling races taking place during the summertime in landscapes with varying altitude. Both to minimize detrimental performance effects associated with arterial desaturation occurring at moderate altitudes in elite athletes, respectively, reduce the risk of hyperthermia on hot days, but also as a pre-competition acclimatization strategy to boost blood volume in already highly adapted athletes. The hematological adaptations require weeks of exposure to manifest, but are attractive as an augmented hemoglobin mass may improve arterial oxygen delivery and hence benefit prolonged performances. Altitude training camps have in this context a long history in exercise physiology and are still common practice in elite cycling. However, heat-acclimation training provides an attractive alternative for some athletes either as a stand-alone approach or in combination with altitude. The present paper provides an update and practical perspectives on the potential to utilize hypoxia and heat exposure to optimize hematological adaptations. Furthermore, we will consider temporal aspects both in terms of onset and decay of the adaptations relevant for improved thermoregulatory capacity and respiratory adaptations to abate arterial desaturation during altitude exposure. From focus on involved physiological mechanisms, time course, and responsiveness in elite athletes, we will provide guidance based on our experience from practical implementation in cyclists preparing for prolonged stage races such as the Tour de France.

The effects of intermittent hypoxic training on the aerobic capacity of exercisers: a systemic review and meta-analysis

OBJECTIVE

To systematically review the effects of intermittent hypoxic training on the aerobic capacity of exercisers.

METHODS

PubMed, Embase, The Cochrane Library, and Web of Science databases were electronically searched to collect studies on the effects of intermittent hypoxic training on the aerobic capacity of exercisers from January 1, 2000, to January 12, 2023. Two reviewers independently screened the literature, extracted data, and assessed the risk of bias of the included studies. Then, meta-analysis was performed by using Stata SE 16.0 software.

RESULTS

A total of 19 articles from 27 studies were included. The results of the meta-analysis showed that compared with the control group, the intermittent hypoxic training group had significantly increased maximal oxygen uptake [weighted mean difference = 3.20 (95%CI: 1.33 ~ 5.08)] and hemoglobin [weighted mean difference = 0.25 (95%CI: 0.04 ~ 0.45)].

CONCLUSION

Intermittent hypoxic training can significantly improve the aerobic capacity of exercisers. Due to the limited quantity and quality of the included studies, more high-quality studies are needed to verify the above conclusion.

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.

The Biological Basis of Sex Differences in Athletic Performance: Consensus Statement for the American College of Sports Medicine

ABSTRACT

Biological sex is a primary determinant of athletic performance because of fundamental sex differences in anatomy and physiology dictated by sex chromosomes and sex hormones. Adult men are typically stronger, more powerful, and faster than women of similar age and training status. Thus, for athletic events and sports relying on endurance, muscle strength, speed, and power, males typically outperform females by 10%-30% depending on the requirements of the event. These sex differences in performance emerge with the onset of puberty and coincide with the increase in endogenous sex steroid hormones, in particular testosterone in males, which increases 30-fold by adulthood, but remains low in females. The primary goal of this consensus statement is to provide the latest scientific knowledge and mechanisms for the sex differences in athletic performance. This review highlights the differences in anatomy and physiology between males and females that are primary determinants of the sex differences in athletic performance and in response to exercise training, and the role of sex steroid hormones (particularly testosterone and estradiol). We also identify historical and nonphysiological factors that influence the sex differences in performance. Finally, we identify gaps in the knowledge of sex differences in athletic performance and the underlying mechanisms, providing substantial opportunities for high-impact studies. A major step toward closing the knowledge gap is to include more and equitable numbers of women to that of men in mechanistic studies that determine any of the sex differences in response to an acute bout of exercise, exercise training, and athletic performance.

Use of new paediatric VO2max reference equations to evaluate aerobic fitness in overweight or obese children with congenital heart disease

AIMS

Overweight and obesity in children with congenital heart disease (CHD) represent an alarming cardiovascular risk. Promotion of physical activity and cardiac rehabilitation in this population requires assessing the level of aerobic fitness (VO2max) by a cardiopulmonary exercise test (CPET). Nevertheless, the interpretation of CPET in overweight/obese children with CHD remains challenging as VO2max is affected by both the cardiac condition and the body mass index (BMI). The new paediatric VO2max  Z-score reference equations, based on a logarithmic function of VO2max, height and BMI, were applied to overweight/obese children with a CHD and compared with overweight/obese children without any other chronic condition.

METHODS AND RESULTS

In this cross-sectional controlled study, 344 children with a BMI > 85th percentile underwent a CPET (54% boys; mean age 11.5 ± 3.1 years; 100 CHD; 244 controls). Using the VO2max  Z-score equations, aerobic fitness was significantly lower in obese/overweight CHD children than that in matched obese/overweight control children (-0.43 ± 1.27 vs. -0.01 ± 1.09; P = 0.02, respectively), and the proportion of children with impaired aerobic fitness was significantly more important in obese/overweight CHD children than in matched controls (17% vs.6%, P = 0.02, respectively). The paediatric VO2max  Z-score reference equations also identified specific complex CHD at risk of aerobic fitness impairment (univentricular heart and right outflow tract anomalies). Using Cooper's weight- and height-based linear equations, similar matched-comparisons analyses found no significant group differences.

CONCLUSIONS

As opposed to the existing linear models, the new paediatric VO2max  Z-score equations can discriminate the aerobic fitness of obese/overweight children with CHD from that of obese/overweight children without any chronic disease.

REGISTRATION

ClinicalTrials.gov NCT04815577.

The V˙O2max Legacy of Hill and Lupton (1923)-100 Years On

PURPOSE

One hundred years ago, Hill and Lupton introduced the concept of maximal oxygen uptake (V˙O2max), which is regarded as "the principal progenitor of sports physiology." We provide a succinct overview of the evolvement of research on V˙O2max, from Hill and Lupton's initial findings to current debates on limiting factors for V˙O2max and the associated role of convective and diffusive components. Furthermore, we update the current use of V˙O2max in elite endurance sport and clinical settings. Practical Applications and Conclusions: V˙O2max is a healthy and active centenarian that remains a very important measure in elite endurance sports and additionally contributes as an important vital sign of cardiovascular function and fitness in clinical settings. Over the past 100 years, guidelines for the test protocols and exhaustion criteria, as well as the understanding of limiting factors for V˙O2max, have improved dramatically. Presently, possibilities of accurate and noninvasive determination of the convective versus diffusive components of V˙O2max by wearable sensors represent an important future application. V˙O2max is not only an indicator of cardiorespiratory function, fitness, and endurance performance but also represents an important biomarker of cardiovascular function and health to be included in routine assessment in clinical practice.

The relationship between hemoglobin and [Formula: see text]: A systematic review and meta-analysis

OBJECTIVE

There is widespread agreement about the key role of hemoglobin for oxygen transport. Both observational and interventional studies have examined the relationship between hemoglobin levels and maximal oxygen uptake ([Formula: see text]) in humans. However, there exists considerable variability in the scientific literature regarding the potential relationship between hemoglobin and [Formula: see text]. Thus, we aimed to provide a comprehensive analysis of the diverse literature and examine the relationship between hemoglobin levels (hemoglobin concentration and mass) and [Formula: see text] (absolute and relative [Formula: see text]) among both observational and interventional studies.

METHODS

A systematic search was performed on December 6th, 2021. The study procedures and reporting of findings followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Article selection and data abstraction were performed in duplicate by two independent reviewers. Primary outcomes were hemoglobin levels and [Formula: see text] values (absolute and relative). For observational studies, meta-regression models were performed to examine the relationship between hemoglobin levels and [Formula: see text] values. For interventional studies, meta-analysis models were performed to determine the change in [Formula: see text] values (standard paired difference) associated with interventions designed to modify hemoglobin levels or [Formula: see text]. Meta-regression models were then performed to determine the relationship between a change in hemoglobin levels and the change in [Formula: see text] values.

RESULTS

Data from 384 studies (226 observational studies and 158 interventional studies) were examined. For observational data, there was a positive association between absolute [Formula: see text] and hemoglobin levels (hemoglobin concentration, hemoglobin mass, and hematocrit (P<0.001 for all)). Prespecified subgroup analyses demonstrated no apparent sex-related differences among these relationships. For interventional data, there was a positive association between the change of absolute [Formula: see text] (standard paired difference) and the change in hemoglobin levels (hemoglobin concentration (P<0.0001) and hemoglobin mass (P = 0.006)).

CONCLUSION

These findings suggest that [Formula: see text] values are closely associated with hemoglobin levels among both observational and interventional studies. Although our findings suggest a lack of sex differences in these relationships, there were limited studies incorporating females or stratifying results by biological sex.

Age, sex, endurance capacity, and chronic heart failure affect central and peripheral factors of oxygen uptake measured by non-invasive and continuous technologies: support of pioneer work using invasive or non-continuous measures

Introduction

It is known that maximum oxygen uptake depends on age, sex, endurance capacity, and chronic heart failure. However, due to the required invasive or often applied non-continuous approaches, less is known on underlying central and peripheral factors. Thus, this study aimed to investigate the effects of age, sex, endurance capacity, and chronic heart failure on non-invasively and continuously measured central and peripheral factors of oxygen uptake.

Methods

15 male children (11 ± 1 years), 15 male (24 ± 3 years) and 14 female recreationally active adults (23 ± 2 years), 12 male highly trained endurance athletes (24 ± 3 years), and 10 male elders (59 ± 6 years) and 10 chronic heart failure patients (62 ± 7 years) were tested during a cardiopulmonary exercise test on a cycling ergometer until exhaustion for: blood pressure, heart rate, stroke volume, cardiac output, cardiac power output, vastus lateralis muscle oxygen saturation, and (calculated) arterio-venous oxygen difference. For the non-invasive and continuous measurement of stroke volume and muscle oxygen saturation, bioreactance analysis and near-infrared spectroscopy were used, respectively. A two-factor repeated measure ANOVA and partial eta-squared effect sizes (η p 2 ) were applied for statistical analyses at rest, 80, and 100% of oxygen uptake.

Results

For the age effect, there were statistically significant group differences for all factors (p ≤ .033; η p 2 ≥ .169 ). Concerning sex, there were group differences for all factors (p ≤ .010; η p 2 ≥ .223 ), except diastolic blood pressure and heart rate (p ≥ .698; η p 2 ≤ .006 ). For the effect of endurance capacity, there were no group differences for any of the factors (p ≥ .065; η p 2 ≤ .129 ). Regarding chronic heart failure, there were group differences for the heart rate and arterio-venous oxygen difference (p ≤ .037; η p 2 ≥ .220 ).

Discussion

Age, sex, endurance capacity, and chronic heart failure affect central and peripheral factors of oxygen uptake measured by non-invasive and continuous technologies. Since most of our findings support pioneer work using invasive or non-continuous measures, the validity of our applied technologies is indirectly confirmed. Our outcomes allow direct comparison between different groups serving as reference data and framework for subsequent studies in sport science and medicine aiming to optimise diagnostics and interventions in athletes and patients.

The relevance of body composition assessment for the rating of perceived exertion in trained and untrained women and men

Introduction: Mechanic power output (MPO) and oxygen consumption (VO2) reflect endurance capacity and are often stated relative to body mass (BM) but less often per skeletal muscle mass (SMM). Rating of perceived exertion (RPE) has previously shown conflicting results between sexes at submaximal intensities. Individual body composition, however, largely differs due to sex and training status. It was the aim of this study to evaluate RPE of untrained and trained individuals of both sexes considering body composition and to estimate whether RPE could be improved as a tool to determine endurance capacity. Methods: The study included 34 untrained adults (age 26.18 ± 6.34 years, 18 women) and 29 endurance trained (age 27.86 ± 5.19, 14 women) who were measured for body composition (InBody 770, InBody Europe B.V., Germany) and tested on a treadmill (Pulsar, H/P/Cosmos, Germany) for aerobic capacity (Metalyzer 3B, Cortex Biophysik GmbH, Germany) in an all-out exercise test applying the Bruce-protocol. VO2, MPO, heart rate (HR), and RPE were obtained at each exercise stage. VO2 and MPO were calculated per BM and SMM. RPE values were correlated with absolute VO2 and MPO, as well as relative to BM, and SMM. HR values and the parameters' standardized values served for comparison to standard procedures. Results: VO2 and MPO were higher in men compared to women and in trained compared to untrained participants. No differences between groups and sexes exist when VO2 and MPO were calculated per BM. When calculated per SMM, VO2 and MPO indicate opposite results already at low intensity stages of exercise test. RPE values had highest correlation with MPO per SMM (R2 = 0.8345) compared to absolute MPO (R2 = 0.7609), or MPO per BM (R2 = 0.8176). Agreement between RPE and MPO per SMM was greater than between RPE and HR (p = 0.008). Conclusion: Although RPE represents a subjective value at first glance, it was shown that RPE constitutes a valuable tool to estimate endurance capacity, which can be further enhanced if individual body composition is considered. Furthermore, MPO and VO2 should be considered relative to SMM. These findings might help to avoid over-exertion, especially among untrained people, by adjusting the training intensity for each subject according to the individual strain evaluated in an exercise test based on individual body composition.

Accuracy of a Clinical Applicable Method for Prediction of VO2max Using Seismocardiography

Cardiorespiratory fitness measured as ˙VO2max is considered an important variable in the risk prediction of cardiovascular disease and all-cause mortality. Non-exercise ˙VO2max prediction models are applicable, but lack accuracy. Here a model for the prediction of ˙VO2max using seismocardiography (SCG) was investigated. 97 healthy participants (18-65 yrs., 51 females) underwent measurement of SCG at rest in the supine position combined with demographic data to predict ˙VO2max before performing a graded exercise test (GET) on a cycle ergometer for determination of ˙VO2max using pulmonary gas exchange measurements for comparison. Accuracy assessment revealed no significant difference between SCG and GET ˙VO2max (mean±95% CI; 38.3±1.6 and 39.3±1.6 ml·min-1·kg-1, respectively. P=0.075). Further, a Pearson correlation of r=0.73, a standard error of estimate (SEE) of 5.9 ml·min-1·kg-1, and a coefficient of variation (CV) of 8±1% were found. The SCG ˙VO2max showed higher accuracy, than the non-exercise model based on the FRIENDS study, when this was applied to the present population (bias=-3.7±1.3 ml·min-1·kg-1, p<0.0001. r=0.70. SEE=7.4 ml·min-1·kg-1, and CV=12±2%). The SCG ˙VO2max prediction model is an accurate method for the determination of ˙VO2max in a healthy adult population. However, further investigation on the validity and reliability of the SCG ˙VO2max prediction model in different populations is needed for consideration of clinical applicability.

Cardiorespiratory fitness and body fat percentage in young adults

Relevance. Maximal oxygen consumption (VO2max) is the maximum amount of oxygen an individual can breathe in and utilize it to produce energy aerobically. The global epidemic of overweight and obesity -’globesity’ is emerging as a public health problem in many parts of the world. Almost 30-65 % of adult urban Indians is either overweight or obese or has abdominal obesity. Recently, cardiovascular ailments are increasing in the younger generation. Low levels of cardiovascular fitness and unfavorable cardiovascular risk profiles are detected in them. Total body fatness and aerobic capacity are frequently used in association with each other and it is often implied that these parameters are strongly inter-related. Both body fatness and status aerobic fitness have been shown to be risk factors for future health outcomes. The aim of this study was to assess the correlation of cardio-respiratory fitness with body fat percentage in young adults. Materials and Methods. This was a pilot study conducted in a group of 100 subjects of age group 18 to 25 years. Ethical clearance was obtained from institutional ethical committee and written informed consent were taken from all subjects participated in the study. Following parameters were taken (a) anthropometric parameters, (b) body fat percentage, (c) physical activity level and (d) VO2max. Results and Discussion. The mean ± SD for age, height, weight, global physical activity questionnaire (GPAQ score) and VO2max was found to be higher in male participants as compared to female participants while BMI was almost equal in both the genders but body fat percentage was higher in female participants. There was positive non-significant correlation of VO2max with body mass index and global physical activity in female subjects but positive significant in male subjects. And moderate negative correlation between body fat percentage and VO2max in male and female subjects but not significant (p 0.05). Conclusion. Body fat percentage was negatively correlated with maximum oxygenconsumption (VO2 max).

Effects of gypenoside L-containing Gynostemma pentaphyllum extract on fatigue and physical performance: A double-blind, placebo-controlled, randomized trial

This study was conducted to investigate the effect of Gynostemma pentaphyllum extract containing gypenoside L (GPE) on improving the cognitive aspects of fatigue and performance of the motor system. One hundred healthy Korean adults aged 19-60 years were randomized to the treatment (GPE for 12 weeks) and control groups, and efficacy and safety-related parameters were compared between the two groups. Maximal oxygen consumption (VO₂ max) and O₂ pulse were significantly higher in the treatment group than in the control group (p = 0.007 and p = 0.047, respectively). After 12 weeks, the treatment group showed significant changes such as decreases in the levels of free fatty acids (p = 0.042). In addition, there were significant differences in the rating of perceived exertion (RPE) (p < 0.05) and value of temporal fatigue between the treatment and control groups on the multidimensional fatigue scale (p < 0.05). Moreover, the level of endothelial nitric oxide synthase (eNOS) in the blood was significantly higher in the treatment group than in the control group (p = 0.047). In summary, oral administration of GPE has a positive effect on resistance to exercise-induced physical and mental fatigue.

Cardiorespiratory Fitness and All-Cause Mortality in Women with Metabolic Syndrome

Purpose: To examine the association between cardiorespiratory fitness (fitness) and all-cause mortality in women with metabolic syndrome (MetSyn). Methods: The sample included 1798 women with MetSyn (mean age 50.2 years) who received a comprehensive preventive baseline examination between 1978 and 2016, with mortality follow-up through December 31, 2017. MetSyn was identified using Adult Treatment Panel-III Guidelines. Fitness was determined by duration of a maximal treadmill exercise test and grouped as fit or unfit on the basis of the upper 80% and lower 20% of the age-standardized fitness distribution. Age- and smoking-adjusted hazard ratios (HRs) with 95% confidence intervals (CIs) were estimated in a proportional hazards regression model. Results: During a mean follow-up of 16.6 ± 8.7 years, 204 deaths occurred. Crude all-cause mortality rates were 6.8 and 6.9 deaths per 10,000 woman-years in fit and unfit groups, respectively. The adjusted HR (95% CI) for all-cause mortality in unfit versus fit women (referent) with MetSyn was 1.36 (95% CI 1.01-1.83). Conclusions: Higher levels of fitness significantly attenuate the risk of all-cause mortality in women with MetSyn. In accordance with the American Heart Association scientific statement, to more accurately determine mortality risk in this population, health care professionals should measure or estimate fitness and should strongly encourage women to meet current public health guidelines for physical activity with the goal of reaching higher fitness levels.

Strength training for arterial hypertension treatment: a systematic review and meta-analysis of randomized clinical trials

Cardiovascular diseases are the leading cause of death in the world and arterial hypertension (AH) accounts for 13.8% of deaths caused by cardiovascular diseases. Strength training interventions could be an important alternative tool for blood pressure control, however, consistent evidence and the most effective training protocol for this purpose are yet to be established. The current study used the Cochrane methodology to systematically review randomized controlled trials (RCTs) that investigated the effect of strength training on blood pressure in hypertensive patients. A systematic search was conducted in the PubMed, EMBASE, Scopus, Cochrane Library, and World Health Organization databases. This review included controlled trials that evaluated the effect of strength training for 8 weeks or more in adults with arterial hypertension, published up to December 2020. Data are described and reported as the weighted mean difference of systolic and diastolic pressure and a 95% confidence interval. Protocol registration: PROSPERO registration number CRD42020151269. A total of 14 studies were identified, including a combined total of 253 participants with hypertension. The meta-analysis showed that mean values of systolic blood pressure (SBP) and diastolic blood pressure (DBP) decreased significantly after strength training interventions. The strongest effect of strength training on decreasing blood pressure was observed in protocols with a moderate to vigorous load intensity (> 60% of one-repetition maximum-1RM), a frequency of at least 2 times per week, and a minimum duration of 8 weeks. We concluded that strength training interventions can be used as a non-drug treatment for arterial hypertension, as they promote significant decreases in blood pressure.

Improved Oxygen Uptake Efficiency Parameters Are Not Correlated with VO2peak or Running Economy and Are Not Affected by Omega-3 Fatty Acid Supplementation in Endurance Runners

Peak oxygen uptake (VO_2peak) is one of the most reliable parameters of exercise capacity; however, maximum effort is required to achieve this. Therefore, alternative, and repeatable submaximal parameters, such as running economy (RE), are needed. Thus, we evaluated the suitability of oxygen uptake efficiency (OUE), oxygen uptake efficiency plateau (OUEP) and oxygen uptake efficiency at the ventilatory anaerobic threshold (OUE@VAT) as alternatives for VO_2peak and RE. Moreover, we evaluated how these parameters are affected by endurance training and supplementation with omega-3 fatty acids. A total of 26 amateur male runners completed a 12-week endurance program combined with omega-3 fatty acid supplementation or medium-chain triglycerides as a placebo. Before and after the intervention, the participants were subjected to a treadmill test to determine VO_2peak, RE, OUE, OUEP and OUE@VAT. Blood was collected at the same timepoints to determine eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in erythrocytes. OUE correlated moderately or weakly with VO_2peak (R² = 0.338, p = 0.002) and (R² = 0.226, p = 0.014) before and after the intervention, respectively. There was a weak or no correlation between OUEP, OUE@VAT, VO_2peak and RE despite steeper OUE, increased OUEP and OUE@VAT values in all participants. OUE parameters cannot be treated as alternative parameters for VO_2peak or RE and did not show changes following supplementation with omega-3 fatty acids in male amateur endurance runners.

Effects of different exercise intensities of race-walking on brain functional connectivity as assessed by functional near-infrared spectroscopy

Introduction

Race-walking is a sport that mimics normal walking and running. Previous studies on sports science mainly focused on the cardiovascular and musculoskeletal systems. However, there is still a lack of research on the central nervous system, especially the real-time changes in brain network characteristics during race-walking exercise. This study aimed to use a network perspective to investigate the effects of different exercise intensities on brain functional connectivity.

Materials and methods

A total of 16 right-handed healthy young athletes were recruited as participants in this study. The cerebral cortex concentration of oxyhemoglobin was measured by functional near-infrared spectroscopy in the bilateral prefrontal cortex (PFC), the motor cortex (MC) and occipital cortex (OC) during resting and race-walking states. Three specific periods as time windows corresponding to different exercise intensities were divided from the race-walking time of participants, including initial, intermediate and sprint stages. The brain activation and functional connectivity (FC) were calculated to describe the 0.01-0.1 Hz frequency-specific cortical activities.

Results

Compared to the resting state, FC changes mainly exist between MC and OC in the initial stage, while PFC was involved in FC changes in the intermediate stage, and FC changes in the sprint stage were widely present in PFC, MC and OC. In addition, from the initial-development to the sprint stage, the significant changes in FC were displayed in PFC and MC.

Conclusion

This brain functional connectivity-based study confirmed that hemodynamic changes at different exercise intensities reflected different brain network-specific characteristics. During race-walking exercise, more extensive brain activation might increase information processing speed. Increased exercise intensity could facilitate the integration of neural signals such as proprioception, motor control and motor planning, which may be an important factor for athletes to maintain sustained motor coordination and activity control at high intensity. This study was beneficial to understanding the neural mechanisms of brain networks under different exercise intensities.

Effects of Exercise Training Intensity and Duration on Skeletal Muscle Capillarization in Healthy Subjects: A Meta-analysis

PURPOSE

This study aimed to investigate the effect of intensity and duration of continuous and interval exercise training on capillarization in skeletal muscle of healthy adults.

METHODS

PubMed and Web of Science were searched from inception to June 2021. Eligibility criteria for studies were endurance exercise training >2 wk in healthy adults, and the capillary to fiber ratio (C:F) and/or capillary density (CD) reported. Meta-analyses were performed, and subsequent subgroup analyses were conducted by the characteristics of participants and training scheme.

RESULTS

Fifty-seven trials from 38 studies were included (10%/90%, athletic/sedentary). C:F was measured in 391 subjects from 47 trials, whereas CD was measured in 428 subjects from 50 trials. Exercise training increased C:F (mean difference, 0.33 (95% confidence interval, 0.30-0.37)) with low heterogeneity ( I2 = 45.08%) and CD (mean difference, 49.8 (36.9-62.6) capillaries per millimeter squared) with moderate heterogeneity ( I2 = 68.82%). Compared with low-intensity training (<50% of maximal oxygen consumption (V̇O 2max )), 21% higher relative change in C:F was observed after continuous moderate-intensity training (50%-80% of V̇O 2max ) and 54% higher change after interval training with high intensity (80%-100% of V̇O 2max ) in sedentary subjects. The magnitude of capillary growth was not dependent on training intervention duration. In already trained subjects, no additional increase in capillarization was observed with various types of training.

CONCLUSIONS

In sedentary subjects, continuous moderate-intensity training and interval training with high intensity lead to increases in capillarization, whereas low-intensity training has less effect. Within the time frame studied, no effect on capillarization was established regarding training duration in sedentary subjects. The meta-analysis highlights the need for further studies in athlete groups to discern if increased capillarization can be obtained, and if so, which combination is optimal (time vs intensity).

Cardiac stroke volume in females and its correlation to blood volume and cardiac dimensions

We aimed to continuously determine the stroke volume (SV) and blood volume (BV) during incremental exercise to evaluate the individual SV course and to correlate both variables across different exercise intensities. Twenty-six females with heterogeneous endurance capacities performed an incremental cycle ergometer test to continuously determine the oxygen uptake (V̇O₂), cardiac output (Q̇) and changes in BV. Q̇ was determined by impedance cardiography and resting cardiac dimensions by 2D echocardiography. Hemoglobin mass and BV were determined using a carbon monoxide-rebreathing method. V̇O_2max ranged from 32 to 62 mL·kg⁻¹·min⁻¹. Q̇_max and SV_max ranged from 16.4 to 31.6 L·min⁻¹ and 90–170 mL, respectively. The SV significantly increased from rest to 40% and from 40% to 80% V̇O_2max. Changes in SV from rest to 40% V̇O_2max were negatively (r = −0.40, p = 0.05), between 40% and 80% positively correlated with BV (r = 0.45, p < 0.05). At each exercise intensity, the SV was significantly correlated with the BV and the cardiac dimensions, i.e., left ventricular muscle mass (LVMM) and end-diastolic diameter (LVEDD). The BV decreased by 280 ± 115 mL (5.7%, p = 0.001) until maximum exercise. We found no correlation between the changes in BV and the changes in SV between each exercise intensity. The hemoglobin concentration [Hb] increased by 0.8 ± 0.3 g·dL⁻¹, the capillary oxygen saturation (ScO₂) decreased by 4.0% (p < 0.001). As a result, the calculated arterial oxygen content significantly increased (18.5 ± 1.0 vs. 18.9 ± 1.0 mL·dL⁻¹, p = 0.001). A 1 L higher BV at V̇O_2max was associated with a higher SV_max of 16.2 mL (r = 0.63, p < 0.001) and Q̇_max of 2.5 L·min⁻¹ (r = 0.56, p < 0.01). In conclusion, the SV strongly correlates with the cardiac dimensions, which might be the result of adaptations to an increased volume load. The positive effect of a high BV on SV is particularly noticeable at high and severe intensity exercise. The theoretically expected reduction in V̇O_2max due to lower SV as a consequence of reduced BV is apparently compensated by the increased arterial oxygen content due to a higher [Hb].

Heart Failure With Preserved Ejection Fraction as an Exercise Deficiency Syndrome: JACC Focus Seminar 2/4

Across differing spectrums of cardiac function and cardiac pathologies, there are strong associations between measures of cardiorespiratory fitness and burden of symptoms, quality of life, and prognosis. In this part 2 of a 4-part series, we contend that there is a strong association among physical activity, cardiorespiratory fitness, and cardiac function. We argue that a chronic lack of exercise is a major risk factor for heart failure with preserved ejection fraction in some patients. In support of this hypothesis, increasing physical activity is associated with greater cardiac mass, greater stroke volumes, greater cardiac output and peak oxygen consumption, and fewer clinical events. Conversely, physical inactivity results in cardiac atrophy, reduced output, reduced chamber size, and decreased ability to augment cardiac performance with exercise. Moreover, physical inactivity is a strong predictor of heart failure risk and death. In sum, exercise deficiency should be considered part of the broad heart failure with preserved ejection fraction phenotype.

Sports Obstetrics: Implications of Pregnancy in Elite Sportswomen, a Narrative Review

Increasing numbers of females are participating in elite sports, with a record number having competed at the Tokyo Olympic Games. Importantly, the ages of peak performance and fertility are very likely to coincide; as such, it is inevitable that pregnancy will occur during training and competition. Whilst there is considerable evidence to promote regular exercise in pregnancy, with benefits including a reduction in hypertensive disorders, gestational diabetes, and reduced rates of post-natal depression, few studies have been conducted which include elite athletes. Indeed, there are concerns that high-intensity exercise may lead to increased rates of miscarriage and preterm labour, amongst other pregnancy-related complications. There is minimal guidance on the obstetric management of athletes, and consequently, healthcare professionals frequently adopt a very conservative approach to managing such people. This narrative review summarises the evidence on the antenatal, intrapartum, and postpartum outcomes in elite athletes and provides recommendations for healthcare providers, demonstrating that generally, pregnant athletes can continue their training, with a few notable exceptions. It also summarises the physiological changes that occur in pregnancy and reviews the literature base regarding how these changes may impact performance, with benefits arising from pregnancy-associated cardiovascular adaptations at earlier gestations but later changes causing an increased risk of injury and fatigue.

Limits to Submaximal and Maximal Exercise in Patients with Hypertrophic Cardiomyopathy

BACKGROUND

Patients with hypertrophic cardiomyopathy (HCM) often have reduced exercise capacity, and it is unclear whether cardiovascular regulation during exercise is intact in these patients. We aimed to determine the relationship between cardiac output (Q̇_c) and oxygen uptake (V̇O₂), and stroke volume (SV) reserve in HCMcompared to healthy participants and participants with left ventricular hypertrophy (LVH) but not HCM.

METHODS

Sixteen patients with HCM (48±7 years, 44% female), 16 participants with LVH (49±5 years, 44% female), and 61 healthy controls (CON: 52±5 years, 52% female) completed submaximal steady-state treadmill exercise followed by a maximal exercise test. V̇O₂, Q̇_c,SV and arterio-venous oxygen difference were measured during rest and exercise, and Q̇_c/V̇O₂ slopes were constructed.

RESULTS

The Q̇_c/V̇O₂ slopewas blunted in HCM compared to CON and LVH (HCM 4.9±0.7 vs. CON 5.5± 1.0 [P = 0.027], vs LVH 6.0±1.0AU [P = 0.002]) and participants with HCM had a lower SV reserve (HCM 53±33%, controls 83±33%, LVH 82±22%; HCM vs. controls P = 0.002; HCM vs. LVH P = 0.015). Despite a blunted Q̇_c/V̇O₂ slope, 75% of patients with HCM achieved ≥80% predicted V̇O₂max by augmenting a-vO₂ difference at maximal exercise (16.0±0.8 mL/100mL vs 13.8±2.7 mL/100mL, P = 0.021).

CONCLUSIONS

Patients with HCM do not appropriately match Q̇_c to metabolic demand, primarily due to inadequate stroke volume augmentation. Despite this central limitation, many patients achieve normal exercise capacities by significantly increasing peripheral oxygen extraction.

A change of heart: mechanisms of cardiac adaptation to acute and chronic hypoxia

Over the last 100 years, high‐altitude researchers have amassed a comprehensive understanding of the global cardiac responses to acute, prolonged and lifelong hypoxia. When lowlanders are exposed to hypoxia, the drop in arterial oxygen content demands an increase in cardiac output, which is facilitated by an elevated heart rate at the same time as ventricular volumes are maintained. As exposure is prolonged, haemoconcentration restores arterial oxygen content, whereas left ventricular filling and stroke volume are lowered as a result of a combination of reduced blood volume and hypoxic pulmonary vasoconstriction. Populations native to high‐altitude, such as the Sherpa in Asia, exhibit unique lifelong or generational adaptations to hypoxia. For example, they have smaller left ventricular volumes compared to lowlanders despite having larger total blood volume. More recent investigations have begun to explore the mechanisms underlying such adaptive responses by combining novel imaging techniques with interventions that manipulate cardiac preload, afterload, and/or contractility. This work has revealed the contributions and interactions of (i) plasma volume constriction; (ii) sympathoexcitation; and (iii) hypoxic pulmonary vasoconstriction with respect to altering cardiac loading, or otherwise preserving or enhancing biventricular systolic and diastolic function even amongst high altitude natives with excessive erythrocytosis. Despite these advances, various areas of investigation remain understudied, including potential sex‐related differences in response to high altitude. Collectively, the available evidence supports the conclusion that the human heart successfully adapts to hypoxia over the short‐ and long‐term, without signs of myocardial dysfunction in healthy humans, except in very rare cases of maladaptation.

Exercise Stress Testing in Athletes

Exercise stress testing (EST) is indicated for diagnostic and prognostic purposes in the general population. In athletes, stress tests can also be useful to inform the risk of high-intensity training and competition, to assess athletic conditioning, and to refine training regimens. Many specific indications for EST are unique to athletes. Treadmill and cycle ergometer protocols each have their strengths and disadvantages; extensive protocol customization may be necessary to answer the clinical question at hand. A comprehensive understanding of the available tools for exercise testing, their strengths, and their limitations is crucial to providing cardiovascular care to athletic individuals.

Influence of respiratory loading on left-ventricular function in cervical spinal cord injury

KEY POINTS

Cervical spinal cord injury (C-SCI) alters both the cardiac and respiratory systems, however little is known as to how these systems interact following injury. Here, we manipulated inspiratory or expiratory intrathoracic pressure (ITP) to mechanistically test the role of the respiratory pump on circulatory function in highly-trained individuals with C-SCI and an able-bodied reference group. In individuals with C-SCI, greater ITP during expiratory loading caused dynamic hyperinflation that was associated with impaired left-ventricular filling. More negative ITP during inspiratory loading did not significantly alter left-ventricular volumes in either group. Interventions that prevent dynamic hyperinflation and/or enhance the ability to generate expiratory pressures may help preserve left-ventricular filling in individuals with C-SCI.

ABSTRACT

Cervical spinal cord injury (C-SCI) negatively impacts cardiac and respiratory function. As the heart and lungs are linked via the pulmonary circuit these systems are interdependent. Here, we utilized inspiratory and expiratory loading to assess whether augmenting the respiratory pump improves left-ventricular (LV) filling and output in individuals with motor-complete C-SCI. We hypothesized LV end-diastolic volume (LVEDV) would increase and decrease with inspiratory and expiratory loading, respectively. Participants (C-SCI: 7M/1F, 35±7 years; able-bodied: 7M/1F, 32±6 years) were assessed under five conditions during 45° head-up tilt; unloaded, inspiratory loading with -10 and -20cmH₂ O esophageal pressure (Pes) on inspiration, and expiratory loading with +10 and +20cmH₂ O Pes on expiration. An esophageal balloon catheter monitored Pes and LV structure and function were assessed by echocardiography. In C-SCI only, (1) +20cmH₂ O reduced LVEDV vs. unloaded (81±15 vs. 88±11 mL, p = 0.006); (2) heart rate was higher during +20cmH₂ O compared to unloaded (p = 0.001) and +10cmH₂ O (p = 0.002); (3) cardiac output was higher during +20cmH₂ O than unloaded (p = 0.002); and (4) end-expiratory lung volume was higher during +20cmH₂ O vs. unloaded (63±10 vs. 55±13% total lung capacity, p = 0.003) but was unaffected by inspiratory loading. In both groups, -10 and -20cmH₂ O had no significant effect on LVEDV. These findings suggest greater expiratory positive pressure acutely impairs LV filling in C-SCI, potentially via impaired venous return, mediastinal constraint and/or direct ventricular interaction subsequent to dynamic hyperinflation. Inspiratory loading did not significantly improve LV function in C-SCI and neither inspiratory nor expiratory loading affected cardiac function or lung volumes in able-bodied participants. Abstract figure legend Background: Cervical spinal cord injury (C-SCI) alters both the cardiac and respiratory systems. However, expiratory function is compromised to a greater extent than inspiratory function. Experimental set up: To examine how the cardiac and respiratory systems interact following C-SCI we manipulated inspiratory or expiratory intrathoracic pressure (ITP) to mechanistically test how changes in ITP and lung volumes influence cardiac function in highly-trained individuals with C-SCI and an able-bodied reference group. Participants were assessed under five conditions during 45° head-up tilt; unloaded, two inspiratory loading, and two expiratory loading conditions.

KEY FINDINGS

Following C-SCI, greater ITP during expiratory loading increased lung volumes and was associated with impaired left-ventricular filling. Interventions that prevent increases in lung volumes and/or enhance the ability to generate expiratory pressures may help preserve left-ventricular filling in individuals with C-SCI. A portion of this figure was created with biorender.com This article is protected by copyright. All rights reserved.

Temporal Skin Temperature as an Indicator of Cardiorespiratory Fitness Assessed with Selected Methods

The aim of this study was to determine whether there are associations between cardiovascular fitness (and aerobic capacity) and changes in temporal skin temperature during and after a single bout of high-intensity exercise. Twenty-three men with varying levels of physical activity (VO2max: 59.03 ± 11.19 (mL/kg/min), body mass 71.5 ± 10.4 (kg), body height 179 ± 8 (cm)) participated in the study. Each subject performed an incremental test and, after a 48-h interval, a 110%Pmax power test combined with an analysis of the thermal parameters, heart rate recovery and heart rate variability. Thermal radiation density from the body surface (temple) was measured using a Sonel KT384 thermal imaging camera immediately after warm-up (Tb), immediately after exercise (Te) and 120 sec after the end of exercise (Tr). The differences between measurements were then calculated. The correlation analysis between the thermal and cardiovascular function parameters during the recovery period showed strong positive associations between the Tr-Te difference and measures of cardiovascular fitness (50 < r < 69, p < 0.05). For example, the correlation coefficient between Tr-Te and VO2max reached 0.55 and between Tr-Te and Pmax reached 0.68. The results obtained indicate that the measurement of temporal temperature during and after an intense 3-min bout of exercise can be used to assess aerobic physical capacity and cardiovascular fitness.

Matching of O2 Utilization and O2 Delivery in Contracting Skeletal Muscle in Health, Aging, and Heart Failure

Skeletal muscle is one of the most dynamic metabolic organs as evidenced by increases in metabolic rate of >150-fold from rest to maximal contractile activity. Because of limited intracellular stores of ATP, activation of metabolic pathways is required to maintain the necessary rates of ATP re-synthesis during sustained contractions. During the very early phase, phosphocreatine hydrolysis and anaerobic glycolysis prevails but as activity extends beyond ∼1 min, oxidative phosphorylation becomes the major ATP-generating pathway. Oxidative metabolism of macronutrients is highly dependent on the cardiovascular system to deliver O₂ to the contracting muscle fibres, which is ensured through a tight coupling between skeletal muscle O₂ utilization and O₂ delivery. However, to what extent O₂ delivery is ideal in terms of enabling optimal metabolic and contractile function is context-dependent and determined by a complex interaction of several regulatory systems. The first part of the review focuses on local and systemic mechanisms involved in the regulation of O₂ delivery and how integration of these influences the matching of skeletal muscle O₂ demand and O₂ delivery. In the second part, alterations in cardiovascular function and structure associated with aging and heart failure, and how these impact metabolic and contractile function, will be addressed. Where applicable, the potential of exercise training to offset/reverse age- and disease-related cardiovascular declines will be highlighted in the context of skeletal muscle metabolic function. The review focuses on human data but also covers animal observations.

JA, Duque L, Chaves-Gomez S, Cristancho-Mejía E, Schmidt WFJ. Hemoglobin Mass, Blood Volume and VO2max of Trained and Untrained Children and Adolescents Living at Different Altitudes

Introduction: To a considerable extent, the magnitude of blood volume (BV) and hemoglobin mass (Hbmass) contribute to the maximum O2-uptake (VO2max), especially in endurance-trained athletes. However, the development of Hbmass and BV and their relationships with VO2max during childhood are unknown. The aim of the present cross-sectional study was to investigate Hbmass and BV and their relationships with VO2max in children and adolescents. In addition, the possible influence of endurance training and chronic hypoxia was evaluated.

Methods: A total of 475 differently trained children and adolescents (girls n = 217, boys n = 258; untrained n = 171, endurance trained n = 304) living at two different altitudes (∼1,000 m, n = 204, ∼2,600 m, n = 271) and 9–18 years old participated in the study. The stage of puberty was determined according to Tanner; Hbmass and BV were determined by CO rebreathing; and VO2max was determined by cycle ergometry and for runners on the treadmill.

Results: Before puberty, there was no association between training status and Hbmass or BV. During and after puberty, we found 7–10% higher values in the trained groups. Living at a moderate altitude had a uniformly positive effect of ∼7% on Hbmass in all groups and no effect on BV. The VO2max before, during and after puberty was strongly associated with training (pre/early puberty: boys +27%, girls +26%; mid puberty: +42% and +45%; late puberty: +43% and +47%) but not with altitude. The associated effects of training in the pre/early pubertal groups were independent of Hbmass and BV, while in the mid- and late pubertal groups, 25% of the training effect could be attributed to the elevated Hbmass.

Conclusions: The associated effects of training on Hbmass and BV, resulting in increased VO2max, can only be observed after the onset of puberty.

Parkinson's disease and intensive exercise therapy - An updated systematic review and meta-analysis

In 2015, Uhrbrand et al. published the first review on Parkinson´s disease (PD) and exercise entirely based on randomized controlled trials (RCT) applying strict exercise definitions. The present review aimed to update the PD literature by assessing the effects of different intensive exercise modalities: resistance training (RT), endurance training (ET), and other intensive exercise modalities (OITM). An updated systematic literature search identified 33 new RCTs. Qualitative and quantitative analyses were performed. A total of 18 RT, 14 ET, and 1 OITM studies were identified (adding to the 8 RT, 6 ET, and 4 OITM studies identified by Uhrbrand et al. in 2015). RT, ET, and OITM were feasible, safe, and did not worsen PD symptoms. Furthermore, RT, ET, and OITM may positively affect functional outcomes (e.g., balance) and depressive symptoms in PD but inconsistencies across these findings warrant cautious conclusions. Meta-analyses showed that RT had a positive impact on muscle strength (standardized mean difference (SMD) = 0.83 [95% CI;0.54, 1.12]), functional capacity (Timed Up and Go Test (TUG): SMD = -0.62 [-1.01, -0.24]), and quality of life (SMD = -0.41 [-0.72, -0.09]), while ET had a positive impact on cardiorespiratory fitness (SMD = 0.27 [0.07, 0.47]) and functional capacity (TUG: SMD = -0.21 [-0.46, 0.04], 6-Min Walk Test: SMD = 0.89 [0.17, 1.62]), and a potentially positive impact on "on-medication" UPDRS-III (SMD = -0.15 [-0.38, 0.09]) and "off-medication" UPDRS-III (SMD = -0.19 [-0.41, 0.04]). In conclusion, RT, ET, and OITM all represent safe, feasible, and beneficial adjunct rehabilitation strategies in PD, with particularly RT and ET showing solid effects.

High Intensity Interval Training: A Potential Method for Treating Sarcopenia

Sarcopenia, an age-related disease characterized by loss of muscle strength and muscle mass, has attracted the attention of medical experts due to its severe morbidity, low living quality, high expenditure of health care, and mortality. Traditionally, persistent aerobic exercise (PAE) is considered as a valid way to attenuate muscular atrophy. However, nowadays, high intensity interval training (HIIT) has emerged as a more effective and time-efficient method to replace traditional exercise modes. HIIT displays comprehensive effects on exercise capacity and skeletal muscle metabolism, and it provides a time-out for the recovery of cardiopulmonary and muscular functions without causing severe adverse effects. Studies demonstrated that compared with PAE, HIIT showed similar or even higher effects in improving muscle strength, enhancing physical performances and increasing muscle mass of elder people. Therefore, HIIT might become a promising way to cope with the age-related loss of muscle mass and muscle function. However, it is worth mentioning that no study of HIIT was conducted directly on sarcopenia patients, which is attributed to the suspicious of safety and validity. In this review, we will assess the effects of different training parameters on muscle and sarcopenia, summarize previous papers which compared the effects of HIIT and PAE in improving muscle quality and function, and evaluate the potential of HIIT to replace the status of PAE in treating old people with muscle atrophy and low modality; and point out drawbacks of temporary experiments. Our aim is to discuss the feasibility of HIIT to treat sarcopenia and provide a reference for clinical scientists who want to utilize HIIT as a new way to cope with sarcopenia.

Genetics and sports performance: the present and future in the identification of talent for sports based on DNA testing

The impact of genetics on physiology and sports performance is one of the most debated research aspects in sports sciences. Nearly 200 genetic polymorphisms have been found to influence sports performance traits, and over 20 polymorphisms may condition the status of the elite athlete. However, with the current evidence, it is certainly too early a stage to determine how to use genotyping as a tool for predicting exercise/sports performance or improving current methods of training. Research on this topic presents methodological limitations such as the lack of measurement of valid exercise performance phenotypes that make the study results difficult to interpret. Additionally, many studies present an insufficient cohort of athletes, or their classification as elite is dubious, which may introduce expectancy effects. Finally, the assessment of a progressively higher number of polymorphisms in the studies and the introduction of new analysis tools, such as the total genotype score (TGS) and genome-wide association studies (GWAS), have produced a considerable advance in the power of the analyses and a change from the study of single variants to determine pathways and systems associated with performance. The purpose of the present study was to comprehensively review evidence on the impact of genetics on endurance- and power-based exercise performance to clearly determine the potential utility of genotyping for detecting sports talent, enhancing training, or preventing exercise-related injuries, and to present an overview of recent research that has attempted to correct the methodological issues found in previous investigations.

Biomarkers and genetic polymorphisms associated with maximal fat oxidation during physical exercise: implications for metabolic health and sports performance

The maximal fat oxidation rate (MFO) assessed during a graded exercise test is a remarkable physiological indicator associated with metabolic flexibility, body weight loss and endurance performance. The present review considers existing biomarkers related to MFO, highlighting the validity of maximal oxygen uptake and free fatty acid availability for predicting MFO in athletes and healthy individuals. Moreover, we emphasize the role of different key enzymes and structural proteins that regulate adipose tissue lipolysis (i.e., triacylglycerol lipase, hormone sensitive lipase, perilipin 1), fatty acid trafficking (i.e., fatty acid translocase cluster of differentiation 36) and skeletal muscle oxidative capacity (i.e., citrate synthase and mitochondrial respiratory chain complexes II-V) on MFO variation. Likewise, we discuss the association of MFO with different polymorphism on the ACE, ADRB3, AR and CD36 genes, identifying prospective studies that will help to elucidate the mechanisms behind such associations. In addition, we highlight existing evidence that contradict the paradigm of a higher MFO in women due to ovarian hormones activity and highlight current gaps regarding endocrine function and MFO relationship.

Leveraging Spaceflight to Advance Cardiovascular Research on Earth

The direct (eg, radiation, microgravity) and indirect (eg, lifestyle perturbations) effects of spaceflight extend across multiple systems resulting in whole-organism cardiovascular deconditioning. For over 50 years, National Aeronautics and Space Administration has continually enhanced a countermeasures program designed to characterize and offset the adverse cardiovascular consequences of spaceflight. In this review, we provide a historical overview of research evaluating the effects of spaceflight on cardiovascular health in astronauts and outline mechanisms underpinning spaceflight-related cardiovascular alterations. We also discuss how spaceflight could be leveraged for aging, industry, and model systems such as human induced pluripotent stem cell-derived cardiomyocytes, organoid, and organ-on-a-chip technologies. Finally, we outline the increasing opportunities for scientists and clinicians to engage in cardiovascular research in space and on Earth.

Differences in Cardiac Output and Aerobic Capacity Between Sexes Are Explained by Blood Volume and Oxygen Carrying Capacity

Whether average sex differences in cardiorespiratory fitness can be mainly explained by blood inequalities in the healthy circulatory system remains unresolved. This study evaluated the contribution of blood volume (BV) and oxygen (O₂) carrying capacity to the sex gap in cardiac and aerobic capacities in healthy young individuals. Healthy young women and men (n = 28, age range = 20–43 years) were matched by age and physical activity. Echocardiography, blood pressures, and O₂ uptake were measured during incremental exercise. Left ventricular end-diastolic volume (LVEDV), stroke volume (SV), cardiac output (Q), peak O₂ uptake (VO_2peak), and BV were assessed with precise methods. The test was repeated in men after blood withdrawal and reduction of O₂ carrying capacity, reaching women’s levels. Before blood normalization, exercise cardiac volumes and output (LVEDV, SV, Q) adjusted by body size and VO_2peak (42 ± 9 vs. 50 ± 11 ml⋅min^–1⋅kg^–1, P < 0.05) were lower in women relative to men. Blood normalization abolished sex differences in cardiac volumes and output during exercise (P ≥ 0.100). Likewise, VO_2peak was similar between women and men after blood normalization (42 ± 9 vs. 40 ± 8 ml⋅min^–1⋅kg^–1, P = 0.416). In conclusion, sex differences in cardiac output and aerobic capacity are not present in experimental conditions matching BV and O₂ carrying capacity between healthy young women and men.

Cardiac Cachexia: Unaddressed Aspect in Cancer Patients

Tumor-derived cachectic factors such as proinflammatory cytokines and neuromodulators not only affect skeletal muscle but also affect other organs, including the heart, in the form of cardiac muscle atrophy, fibrosis, and eventual cardiac dysfunction, resulting in poor quality of life and reduced survival. This article reviews the holistic approaches of existing diagnostic, pathophysiological, and multimodal therapeutic interventions targeting the molecular mechanisms that are responsible for cancer-induced cardiac cachexia. The major drivers of cardiac muscle wasting in cancer patients are autophagy activation by the cytokine-NFkB, TGF β-SMAD³, and angiotensin II-SOCE-STIM-Ca²⁺ pathways. A lack of diagnostic markers and standard treatment protocols hinder the early diagnosis of cardiac dysfunction and the initiation of preventive measures. However, some novel therapeutic strategies, including the use of Withaferin A, have shown promising results in experimental models, but Withaferin A’s effectiveness in human remains to be verified. The combined efforts of cardiologists and oncologists would help to identify cost effective and feasible solutions to restore cardiac function and to increase the survival potential of cancer patients.

The physiological and clinical importance of cardiorespiratory fitness in people with abdominal aortic aneurysm

New Findings

What is the topic of this review?

This review focuses on the physiological impact of abdominal aortic aneurysm (AAA) on cardiorespiratory fitness and the negative consequences of low fitness on clinical outcomes in AAA. We also discuss the efficacy of exercise training for improving cardiorespiratory fitness in AAA.

What advances does it highlight?

We demonstrate the negative impact of low fitness on disease progression and clinical outcomes in AAA. We highlight potential mechanistic determinants of low fitness in AAA and present evidence that exercise training can be an effective treatment strategy for improving cardiorespiratory fitness, postoperative mortality and disease progression.

Abstract

An abdominal aortic aneurysm (AAA) is an abnormal enlargement of the aorta, below the level of the renal arteries, where the aorta diameter increases by >50%. As an aneurysm increases in size, there is a progressive increase in the risk of rupture, which ranges from 25 to 40% for aneurysms >5.5 cm in diameter. People with AAA are also at a heightened risk of cardiovascular events and associated mortality. Cardiorespiratory fitness is impaired in people with AAA and is associated with poor (postoperative) clinical outcomes, including increased length of hospital stay and postoperative mortality after open surgical or endovascular AAA repair. Although cardiorespiratory fitness is a well‐recognized prognostic marker of cardiovascular health and mortality, it is not assessed routinely, nor is it included in current clinical practice guidelines for the management of people with AAA. In this review, we discuss the physiological impact of AAA on cardiorespiratory fitness, in addition to the consequences of low cardiorespiratory fitness on clinical outcomes in people with AAA. Finally, we summarize current evidence for the effect of exercise training interventions on cardiorespiratory fitness in people with AAA, including the associated improvements in postoperative mortality, AAA growth and cardiovascular risk. Based on this review, we propose that cardiorespiratory fitness should be considered as part of the routine risk assessment and monitoring of people with AAA and that targeting improvements in cardiorespiratory fitness with exercise training might represent a viable adjunct treatment strategy for reducing postoperative mortality and disease progression.

Davies R. The Effect of Exercise Training Intensity on VO2max in Healthy Adults: An Overview of Systematic Reviews and Meta-Analyses

This study aimed to evaluate systematic reviews and meta-analyses that have examined the effect of exercise training on VO2max in healthy individuals at different intensities. Five databases were searched: EBSCOhost, MEDLINE/PubMed, SPORTDiscus, Web of Science, and Google Scholar. Eligibility criteria for selecting reviews included systematic reviews and meta-analyses of healthy adults that examined the effect of lower intensity training (LIT) and/or high intensity training (HIT) on VO2max. Eleven reviews met the eligibility criteria. All reviews were of moderate-to-very strong methodological quality. The included reviews reported data from 179 primary studies with an average of 23 ± 10 studies per review. All reviews included in this overview showed that exercise training robustly increased VO2max at all intensities. Three meta-analyses that compared LIT versus HIT protocols on VO2max reported small/moderate beneficial effects for HIT over LIT; however, the beneficial effects of HIT on VO2max appear to be moderated by training variables other than intensity (e.g., training impulse, interval length, training volume, and duration) and participants' baseline characteristics (e.g., age and fitness levels). Overall, evidence from this overview suggests that the apparent differences between LIT and HIT protocols on VO2max were either small, trivial, or inconclusive, with several methodological considerations required to standardise research designs and draw definitive conclusions.

Validity of the Wattbike 3-Minute Aerobic Test: Measurement and Estimation of V̇o2max

ABSTRACT

Hanson, NJ, Scheadler, CM, Katsavelis, D, and Miller, MG. Validity of the Wattbike 3-minute aerobic test: measurement and estimation of V̇o2max. J Strength Cond Res 36(2): 400-404, 2022-The Wattbike includes a 3-minute aerobic test (3mAT) along with an estimation of V̇o2max. The estimation equation that is used is from a previous study using a different protocol and sedentary subjects. The purpose of this study was to determine whether (a) the 3mAT is able to elicit V̇o2max, and (b) whether this estimation is accurate. Thirteen cyclists (10 men; age: 29.2 ± 10.0 years, height 178.7 ± 8.3 cm, and mass 75.1 ± 12.5 kg) with a range of experience volunteered for this study. At the first visit, a self-paced V̇o2max (SPV) test was performed to obtain the "true" V̇o2max. At the second session, subjects completed the 3mAT. Primary dependent variables included maximal values of oxygen consumption (V̇o2), carbon dioxide production (V̇co2), heart rate (HR), ventilation (VE), and respiratory exchange ratio (RER). A repeated-measures analysis of variance showed no difference (p = 0.367) between V̇o2max values (3mAT estimation: 54.3 ± 9.3 ml·kg-1·min-1, 3mAT measured: 52.5 ± 8.7, SPV: 54.0 ± 9.7). Paired-samples t-tests showed that HR (p = 0.027) was higher in the SPV (184.7 ± 10.6 vs. 180.9 ± 6.3 b·min-1), whereas RER and V̇co2 were both higher in the 3mAT (1.29 ± 0.10 vs. 1.19 ± 0.06 and 4.92 ± 1.01 vs. 4.62 ± 0.98, respectively; both p < 0.05). The intraclass correlation between the V̇o2max measured from the SPV and 3mAT was 0.96 (95% CI: 0.88-0.99, p < 0.001), and between the 3mAT measured and estimated values was 0.91 (95% CI: 0.71-0.97 p < 0.001). If an athlete has access to a Wattbike, they can complete the 3mAT, receive their V̇o2max estimation, and be confident of its accuracy.