Maximal Cardiac Output Research Articles

Development potentials of commonly used high-intensity training strategies on central and peripheral components of maximal oxygen consumption

The aim of this study was to reveal the development potentials of five high-intensity training models on central and peripheral components of maximal oxygen consumption (VO2max). Following VO2max determination, maximal cardiac output (Qmax), maximal stroke volume (SVmax), and maximal arteriovenous O2 difference (a−vO2diff_max) were analysed. Short-interval- (short-HIIT), long-interval (long-HIIT), alternating work-rate continuous (alter-HIT), constant work-rate continuous (const-HIT), and sprint interval (SIT) sessions were performed on separate days with iso-effort and iso-time methods. Time spent (tspent) at > 95% of VO2max was the highest in long-HIIT (p < 0.05). The tspent at > 90% of Qmax was higher in alter-HIT than long-HIIT and SIT (p < 0.05), while there was no significant difference for tspent at > 90% of SVmax amongst high-intensity trainings. The tspent at > 90% of a−vO2diff_max was higher in short-HIIT and long-HIIT than other modalities (p < 0.05). It can be said that continuous modalities seem to have a higher potential to improve central part of VO2max, while interval modalities may be better to develop peripheral component.

Effects of a New Form of Resistance-Type High-Intensity Interval Training on Cardiac Structure, Hemodynamics, and Physiological and Performance Adaptations in Well-Trained Kayak Sprint Athletes.

This study examined the effects of a resistance-type high-intensity interval training (RHIIT) matched with the lowest velocity that elicited O2peak (100% vO2peak) in well-trained kayak sprint athletes. Responses in cardiac structure and function, cardiorespiratory fitness, anaerobic power, exercise performance, muscular strength, and hormonal adaptations were examined. Male kayakers (n = 24, age: 27 ± 4 years) were randomly assigned to one of three 8-wk conditions (N = 8): (RHIIT) resistance training using one-armed cable row at 100% vO2peak; paddling-based HIIT (PHIIT) six sets of paddling at 100% vO2peak; or controls (CON) who performed six sessions including 1-h on-water paddling/sessions at 70–80% maximum HR per week. Significant increases (p < 0.05) in O2peak, vO2peak, maximal cardiac output, resting stroke volume, left ventricular end-systolic dimension, 500-m paddling performance were seen pre- to post-training in all groups. Change in O2peak in response to PHIIT was significantly greater (p = 0.03) compared to CON. Also, 500-m paddling performance changes in response to PHIIT and RHIIT were greater (p = 0.02, 0.05, respectively) than that of CON. Compared with pre-training, PHIIT and RHIIT resulted in significant increases in peak and average power output, maximal stroke volume, end-diastolic volume, ejection fraction, total testosterone, testosterone/cortisol ratio, and 1,000-m paddling performance. Also, the change in 1,000-m paddling performance in response to PHIIT was significantly greater (p = 0.02) compared to that of CON. Moreover, maximum strength was significantly enhanced in response to RHIIT pre- to post-training (p < 0.05). Overall, RHIIT and PHIIT similarly improve cardiac structure and hemodynamics, physiological adaptations, and performance of well-trained kayak sprint athletes. Also, RHIIT enhances cardiorespiratory fitness and muscular strength simultaneously.

Improvements in Maximal Oxygen Uptake After Sprint-Interval Training Coincide with Increases in Central Hemodynamic Factors.

Sprint-interval training has been shown to improve maximal oxygen uptake, in part through peripheral muscle adaptations that increase oxygen utilization. In contrast, the adaptations of central hemodynamic factors in this context remain unexplored. The aim of the current study was to explore the effects of sprint-interval training on maximal oxygen uptake and central hemodynamic factors. Healthy men and women (n = 29; mean age, 27 ± 5 yr; height, 175 ± 8 cm; body mass, 72.5 ± 12.0 kg) performed 6 wk of sprint-interval training consisting of three weekly sessions of 10-min low-intensity cycling interspersed with 3 × 30-s all-out sprints. Maximal oxygen uptake, total blood volume, and maximal cardiac output were measured before and after the intervention. Maximal oxygen uptake increased by 10.3% (P < 0.001). Simultaneously, plasma volume, blood volume, total hemoglobin mass, and cardiac output increased by 8.1% (276 ± 234 mL; P < 0.001), 6.8% (382 ± 325 mL; P < 0.001), 5.7% (42 ± 41 g; P < 0.001), and 8.5% (1.0 ± 0.9 L·min-1; P < 0.001), respectively. Increased total hemoglobin mass along with measures of body surface area had a significant impact on the improvements in maximal oxygen uptake. Six weeks of sprint-interval training results in significant increases in hemoglobin mass, blood volume, and cardiac output. Because these changes were associated with marked improvements in maximal oxygen uptake, we conclude that central hemodynamic adaptations contribute to the improvement in maximal oxygen uptake during sprint-interval training.

Effect of Interval Training on the Factors Influencing Maximal Oxygen Consumption: A Systematic Review and Meta-Analysis.

The maximal rate of oxygen consumption (VO2max) is an important measure in exercise science as it is an indicator of cardiorespiratory fitness. Individual studies have identified central and peripheral adaptions to interval training that may underlie improvements in VO2max, but there is no compilation of results. We aimed to systematically review the adaptive responses to high-intensity interval training (HIIT) and sprint interval training (SIT) on the central and peripheral factors influencing VO2max in healthy individuals. SPORTDiscus and MEDLINE (up to and including 13 June, 2020) were explored to conduct the literature search. Reviewed studies met the following criteria: (1) were in the English language; (2) prospective in nature; (3) included at least three interval sessions or were at least 1week in duration; (4) contained HIIT or SIT; (5) involved participants between the ages of 18 and 65years; and (6) included at least one of the following central (blood volume, plasma volume, hemoglobin mass, left ventricular mass, maximal stroke volume, maximal cardiac output) or peripheral factors (capillary density, maximal citrate synthase activity, mitochondrial respiration associated with VO2max). Thirty-two studies (369 participants, 49 were female) were included in the quantitative analyses, consisting of both HIIT (n = 18) and SIT (n = 17) interventions. There were only statistically significant changes in hematological measures (plasma volume) following HIIT. There was a significant increase in left ventricular mass following HIIT (7.4%, p < 0.001) and SIT (5.3%, p = 0.007) in inactive individuals, though the change following SIT may be misleading. There was only a significant increase in maximal stroke volume (14.1%, p = 0.015) and maximal cardiac output (12.6%, p = 0.002) following HIIT. In addition to central factors, there was a significant increase in capillary density (13.8%, p < 0.001) following SIT in active individuals. With respect to maximal citrate synthase activity, there were improvements following HIIT (20.8%, p < 0.001) and SIT (15.7%, p < 0.001, I2 = 97%) in active individuals. The results for mitochondrial respiration suggested that there was no statistically significant improvement following HIIT (5.0%, p = 0.585). Improvements in the central and peripheral factors influencing VO2max were dependent on the interval type. Only HIIT led to a statistically significant improvement in cardiac function. Both HIIT and SIT increased maximal citrate synthase activity, while changes in other peripheral measures (capillary density, mitochondrial respiration) only occurred with SIT.

Physiological Adaptations to High-Intensity Interval Training Combined with Blood Flow Restriction in Masters Road Cyclists.

High-intensity interval training (HIIT) and blood flow restriction (BFR) training have been used to enhance athletic performance and cardiovascular health. Combining these training modalities might be an effective training modality for masters athletes who seek to enhance athletic performance and to reduce cardiovascular risks. Fifty masters road cyclists age 35-49 yr were randomly assigned to the continuous exercise training (n = 16), continuous plus HIIT (n = 17), and continuous plus BFR training combined with HIIT (BFRIT; n = 17) for 12 wk. Both HIIT and BFRIT were performed on a cycle ergometer twice a week. Maximal oxygen consumption (V̇O2max) increased in the HIIT and BFRIT groups (P < 0.05). This was accompanied by significant improvements in maximal cardiac output and stroke volume (P < 0.05). Forty-kilometer time trial performance improved in all three groups (P < 0.05). Peak power output increased in both HIIT and BFRIT groups (P < 0.05). Flow-mediated dilation in both brachial and popliteal arteries increased in all three groups (all P < 0.05). There were no significant changes in carotid intima-media thickness and arterial stiffness in any of the groups. Total lean mass, muscle cross-sectional area and thickness in rectus femoris and vastus lateralis, and peak torque of isokinetic knee extension increased only in the BFRIT group (all P < 0.05). Tissue saturation index decreased only in the BFRIT group (P < 0.05). Changes in 40-km time trial performance were associated with corresponding changes in V̇O2max (r = -0.312, P = 0.029) and peak isokinetic extensor torque (r = -0.432, P = 0.002). Including HIIT particularly with BFR in the routine continuous training may be more effective in enhancing performance and physiological functions in masters road cyclists.

Exercise Training Combined with Calanus Oil Supplementation Improves the Central Cardiodynamic Function in Older Women.

The aim of this study was to investigate the possible beneficial effects of exercise training (ET) with omega-3/Calanus oil supplementation on cardiorespiratory and adiposity parameters in elderly women. Fifty-five women (BMI: 19–37 kg/m2, 62–80 years old) were recruited and randomly assigned to the 4 month intervention with ET and omega-3 supplementation (Calanus oil, ET-Calanus) or ET and the placebo (sunflower oil; ET-Placebo). The body composition was determined by dual-energy X-ray absorptiometry (DXA), and cardiorespiratory parameters were measured using spiroergometry and PhysioFlow hemodynamic testing. Both interventions resulted in an increased lean mass whereas the fat mass was reduced in the leg and trunk as well as the android and gynoid regions. The content of trunk fat (in percent of the total fat) was lower and the content of the leg fat was higher in the ET-Calanus group compared with the ET-Placebo. Although both interventions resulted in similar improvements in cardiorespiratory fitness (VO2max), it was explained by an increased peripheral oxygen extraction (a-vO2diff) alone in the ET-Placebo group whereas increased values of both a-vO2diff and maximal cardiac output (COmax) were observed in the ET-Calanus group. Changes in COmax were associated with changes in systemic vascular resistance, circulating free fatty acids, and the omega-3 index. In conclusion, Calanus oil supplementation during a 4 month ET intervention in elderly women improved the cardiorespiratory function, which was due to combined central and peripheral cardiodynamic mechanisms.

Revisiting the limitation to with ageing: is mitochondrial (dys)function the key?

Revisiting the limitation to with ageing: is mitochondrial (dys)function the key?

Effect of small vs large muscle mass endurance training on maximal oxygen uptake in organ transplanted recipients

Maximal oxygen consumption (V̇O2max) is impaired in heart (HTx), kidney (KTx), and liver (LTx) transplanted recipients and the contribution of the cardiovascular, central, and peripheral (muscular) factors in affecting V̇O2max improvement after endurance training (ET) has never been quantified in these patients. ET protocols involving single leg cycling (SL) elicit larger improvements of the peripheral factors affecting O2 diffusion and utilization than the double leg (DL) cycling ET. Therefore, this study aimed to compare the effects of SL-ET vs DL-ET on V̇O2max. We determined the DL-V̇O2max and maximal cardiac output before and after 24 SL-ET vs DL-ET sessions on 33 patients (HTx= 13, KTx= 11 and LTx= 9). The DL-V̇O2max increased by 13.8%± 8.7 (p< 0.001) following the SL-ET, due to a larger maximal O2 systemic extraction; meanwhile, V̇O2max in DL-ET increased by 18.6%± 12.7 (p< 0.001) because of concomitant central and peripheral adaptations. We speculate that in transplanted recipients, SL-ET is as effective as DL-ET to improve V̇O2max and that the impaired peripheral O2 extraction and/or utilization play an important role in limiting V̇O2max in these types of patients. Novelty: SL-ET increases V̇O2max in transplanted recipients because of improved peripheral O2 extraction and/or utilization. SL-ET is as successful as DL-ET to improve the cardiorespiratory fitness in transplanted recipients. The model of V̇O2max limitation indicates the peripheral factors as a remarkable limitation to the V̇O2max in these patients.

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 (O2max) 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 O2max 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 O2max 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 O2max (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.

Developing a Large Animal Model of Heart Failure with Preserved Ejection Fraction

Objective Heart failure with preserved ejection fraction (HFpEF) is a clinical syndrome representing more than 50% of heart failure cases. Currently, available treatment options do not improve patient outcomes and the mechanics of HFpEF remain largely misunderstood. This makes animal models of HFpEF a valuable resource and currently there are few animal models that replicate the clinical characteristics of this disease. Previous studies have replicated associated cardiac hypertrophy and diastolic dysfunction, however exercise intolerance is a cardinal sign of HFpEF but is rarely investigated in animal models. The aim of this study was to develop a clinically relevant large animal model of HFpEF using the two-kidney-one-clip renovascular hypertension method and investigate exercise intolerance. We hypothesized that chronic hypertension would lead to a reduced cardiac output (CO) and stunted heart rate (HR) response during exercise. Methods Hypertension (HTN) was induced by clipping of the renal artery in adult female sheep (N=4), while the contralateral kidney remained intact. Sheep were left to develop HTN for 6 weeks, after which sheep were instrumented to record cardiac output (CO), heart rate (HR) and mean arterial pressure (MAP). A normal cohort (N=3) of sheep also underwent this same instrumentation surgery. After recovery from surgery, the animals were acclimatized to walk on a treadmill and following acclimatization, they entered a treadmill protocol where the incline and speed was increased every 3 min. Results Renal artery clipping caused a significant rise in MAP (123±6 mmHg from 77±9 mmHg) while CO was not different. In normotensive sheep exercise led to large changes in CO (17±2 L/min from 9+/-0.7 L/min) and HR (153±15 bpm from 107±14 bpm). Exercise in the hypertensive sheep led to attenuated increases in CO (11+/-1 L/min from 6±0.4 L/min) and HR (137±7 bpm from 115±8 bpm). Interestingly, the hypertensive sheep reached their maximum heart rates earlier than the normotensive sheep. Discussion/Conclusion Our data suggest that chronic hypertension leads to a decrease in the maximum cardiac output reached during exercise suggesting a loss of cardiac reserve. Overall this indicates that the 2-kidney-1-clip renovascular HTN model may be a good method to induce HFpEF.

Abstract 14433: High Intensity Exercise Training Safely Increases Cardiorespiratory Fitness in Patients With Hypertrophic Cardiomyopathy

Introduction: Patients with hypertrophic cardiomyopathy (HCM) are excluded from high intensity activities due to perceived fear of sudden cardiac death. Observational data from athletes with HCM suggest that engaging in high intensity exercise (HIE) may be safe and is associated with higher cardiorespiratory fitness. Whether HIE can safely elicit a superior increase in fitness compared to moderate intensity exercise in patients with HCM is unclear. Methods: Nine HCM patients (49 ± 7 years, 3 female) were assessed for maximal oxygen uptake (VO 2 max, Douglas Bag method), cardiac output (Q c , acetylene rebreathing), and peripheral oxygen extraction (av-O 2 diff, Fick equation) before randomization and after 5 months of MIE or HIE training. Patients completed 3-4 sessions of MIE each week, while the HIE group also incorporated 1-2 supervised high intensity interval training sessions/week from month 3 onwards. Arrhythmias were monitored via pre-existing implantable cardiac defibrillators or implantable loop recorders placed prior to training. Results: Five months of MIE increased absolute VO 2 max by 3% and relative VO 2 max by 4%, while HIE consistently increased absolute VO 2 max by 6% and relative VO 2 max by 5% (Figure). Maximal Q c did not change after MIE but increased in all HIE patients (+1.2L/min, 95% CI -1.4 to 3.9), while maximal av-O 2 diff remained stable in both groups. Training compliance was 84 ± 15% in HIE and 93 ± 11% in MIE. There were no serious exercise-related adverse events in either group though two HIE subjects had arrhythmias at rest: 1) 14-beat run of wide complex tachycardia of uncertain mechanism given underlying conduction disease prior to a training session, and 2) 11 beats of non-sustained ventricular tachycardia prior to post exercise testing. Conclusions: Preliminary findings show that five months of HIE safely and consistently increased cardiorespiratory fitness in patients with HCM, though overall the improvements were comparable to MIE.

From diastolic dysfunction to exercise intolerance: an in silico simulation study on the phenotypic markers of heart failure with preserved ejection fraction

Abstract Background Left ventricular (LV) diastolic dysfunction, i.e. impaired LV relaxation function and/or increased LV stiffness, has been hypothesized to be responsible for at least part of the exercise intolerance in heart failure with preserved ejection fraction (HFpEF). Yet the mechanisms remain largely unknown. Purpose To determine in silico if and how abnormal LV diastolic function causes reduction in maximum cardiac output (COmax), i.e. exercise intolerance. Methods We used a cardiovascular model (CircAdapt) to simulate the effects of impaired LV relaxation and increased LV myocardial stiffness on cardiac hemodynamics. The model was initialized using a reference simulation with hypertension (systolic blood pressure: 150 mmHg) and concentric LV hypertrophy (LV wall mass: +25%). Impaired LV relaxation was introduced by increasing tau from 35 ms to 65 ms. LV stiffness was increased by increasing LV end-diastolic elastance from 0.15 mmHg/ml to 0.60 mmHg/ml and 2.00 mmHg/ml (moderate and severe LV stiffness, respectively). In each simulation, LV ejection fraction (LVEF), E/A ratio and mean left atrial (LA) pressure (mLAP) was assessed. To evaluate the effect on exercise tolerance, COmax was determined by gradually increasing cardiac output and heart rate in a predefined manner until mLAP exceeded 35 mmHg. Results In all simulations, LVEF remained unchanged and preserved (i.e. 60%). In rest, impaired LV relaxation decreased E/A ratio from 1.1 to 0.8 (impaired filling pattern) and increased mLAP from 7.2 mmHg to 8.0 mmHg (Figure top: gray vs. orange). Total LV filling time was reduced at rest, reducing diastolic reserve capacity and thereby of COmax, by 15% compared to the reference (Figure bottom: gray vs. orange). Moderate LV stiffness increased E/A ratio to 1.1 (pseudo-normal filling pattern) and mLAP to 15.0 mmHg (Figure top: gray vs. red). COmax was reduced by 40% due to a steep increase of mLAP with exercise intensity. Severe LV stiffness increased E/A ratio to 2.2 (i.e. restrictive filling pattern), but resulted in a non-physiological mLAP of 40 mmHg at rest. However, when combining moderate LV stiffness with LA dysfunction (i.e. reduced LA contractility and increased LA stiffness) also led to restrictive filling pattern (E/A ratio &amp;gt;2.0) with mLAP 19 mmHg (Figure top: red vs. dashed blue). COmax reduced most severely by 53%, emphasizing the importance of LA function in LV diastolic dysfunction (Figure bottom: gray vs. dashed blue). Conclusions Through variations in LV and LA function, we linked the progression of LV diastolic dysfunction to LV and LA properties. Increased LV stiffness, more than impaired LV relaxation, is associated with substantially reduced exercise tolerance. The combination of LV and LA dysfunction led to the most severe exercise intolerance. Our unique in silico framework enables future studies to investigate other potential cardiac and vascular mechanisms underlying exercise intolerance in HFpEF. Figure 1 Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): This work was funded by the Netherlands Organisation for Scientific Research and the Dutch Heart Foundation.

Effects of low intensity resistance training of blood flow restriction with different occlusion pressure on lower limb muscle and cardiopulmonary function of college students

Objective: The study compared the effects of low intensity resistance training with blood flow restriction (BFR) with different occlusion pressure on lower limb muscle and cardiopulmonary function. Methods: Twenty-seven college students were randomly divided into three groups by different occlusion pressure: 0 mmHg (group C), 120 mmHg (group L) and 180 mmHg (group H). Before and after training (3 times a week for 12 weeks) with an inflatable cuff (20% 1RM, half squat), the muscle thickness(MTH)of rectus femoris and medius femoris, relative peak knee extensor moment(rM), peak power(P), relative maximal oxygen uptake(rVO2max), stroke volume(SV), cardiac output(CO), ejection fraction(EF) and other indicators were measured for all subjects. Results: When compared with pre-training, and rectus femoris, the MTH of medius femoris, rM, rVO2max, SV, CO and EF were significantly increased in group L and group H after 12 weeks training(P＜0.05, P＜0.01), as well as compared with group C after training(P＜0.05, P＜0.01). There was no significant difference between group L and group H after training. Conclusion: BFR training protocols under 120 mmHg or 180 mmHg pressure were effective in improving muscle and cardiopulmonary function.

High Intensity Exercise Training In Patients With Hypertrophic Cardiomyopathy

Patients with hypertrophic cardiomyopathy (HCM) are excluded from high intensity activities due to perceived fear of sudden cardiac death though data from athletes with HCM suggest competitive sport may be safe for some. Low cardiorespiratory fitness in sedentary HCM patients may confer a greater lifetime cardiovascular event risk than exercise per se. While moderate intensity exercise training in patients with HCM modestly increases fitness, high intensity exercise may be superior. PURPOSE: To compare the efficacy of five months of moderate intensity exercise and high intensity exercise training to improve cardiorespiratory fitness (V̇O2max) in patients with HCM. METHODS: Eight patients with HCM (50 ± 7 years, 3 female) were assessed for maximal oxygen uptake (V̇O2max, Douglas Bag method), cardiac output (Q̇c, acetylene rebreathing), and peripheral oxygen extraction (av-O2 diff, Fick equation) before randomization and after 5 months of moderate or high intensity exercise training. Patients completed 3-4 sessions of moderate intensity exercise each week, while the high intensity group also incorporated a weekly interval training session. RESULTS: Five months of moderate intensity exercise increased absolute V̇O2max by 3% and relative V̇O2max by 4%, while high intensity exercise consistently increased absolute V̇O2max by 6% and relative V̇O2max by 5% (Figure). Maximal Q̇c did not change after moderate intensity exercise (+0.0L [95% CI -2.0 to 1.7]) but increased in all three patients after high intensity exercise (+1.2L [95% CI -1.4 to 3.9]), while maximal av-O2 diff remained stable in both groups (moderate intensity: +0.8mL/100mL [95% CI -1.0 to 2.6]; high intensity: -0.5mL/100mL [95% CI -3.6 to 2.7]). CONCLUSION: Preliminary findings show similar increases in cardiorespiratory fitness following five months of moderate and high intensity exercise training in patients with HCM, although improvements were more consistent after high intensity exercise.

SEX DIFFERENCES IN MAXIMAL OXYGEN UPTAKE: WHAT ARE THE BIGGEST CONTRIBUTORS?

Previous investigations in maximal aerobic capacity (VO2max) have attributed sex differences to anatomical and physiological parameters. PURPOSE: To determine the main factor affecting VO2max in a sample of physically active young adults. METHODS: Sixteen college-aged students (18-25 years, 8 males and 8 females) participated in one laboratory visit including body composition, hematocrit (HCT), and VO2max assessment. Lean body mass (LBM) and fat mass (FM) were obtained from a whole-body DEXA scan. Hematocrit (HCT) was determined using a finger prick blood sample and validated by measures of urine specific gravity (USG) to control for hydration status. A graded exercise test was performed on the cycle ergometer using 25 watt (W) per minute and 20 W per minute incremental protocols for men and women respectively. VO2max, cardiac output max (Qmax) and stroke volume max (SVmax) were recorded using the COSMED Quark CPET metabolic cart. Cardiac output was determined using the Fick principle. Test measure means were grouped by sex and analyzed for significance using a one-way ANOVA. A Pearson’s R correlation was performed to determine the association between variables of HCT, LBM, SVmax, Qmax, absolute VO2max. RESULTS: Males showed significantly greater measures of height (177.94 cm ± 5.74 cm vs. 166.6 cm ± 3.1 cm; p<0.01), LBM (63.70 kg ± 7.51 kg vs. 43.85 kg ± 1.90 kg; p<0.01), HCT (46.9% ± 3.5% vs. 42.2% ± 3.0%; p<0.05), absolute VO2max (3.377 L/min ± 0.464L/min vs. 2.439 L/min ± 0.300 L/min; p<0.05), Qmax (20.4 L/min ± 2.3 L/min vs. 14.84 L/min ± 1.80 L/min; p<0.01) and SVmax (110.1 mL ± 13.5 mL vs. 78.24 mL ± 7.47 mL; p<0.01) compared to females. Pearson’s R correlation analysis showed that absolute VO2max (L/min) was positively correlated with Qmax (R= 0.989), SVmax (R= 0.958) and LBM (R= 0.777). CONCLUSIONS: Sex differences in maximal aerobic capacity should be understood predominantly as a consequence of maximal cardiac output and sex-related differences in body size and lean mass.

Short-Term Sprint Interval Training Increases Maximal Oxygen Uptake Without Changing Maximal Cardiac Output

Traditional moderate intensity continuous training increases maximal oxygen uptake (VO2max). This effect is primarily attributed to an increased maximal cardiac output (Qmax), as predicted by the Fick principle. Sprint interval training (SIT) increases VO2max similar to MICT, often despite a lower training volume, but the effect on Qmax is unclear. PURPOSE: To determine the effect of 6 sessions of SIT over 2 wk on VO2max, Qmax and exercise performance in healthy, untrained adults [n=12 (9 females); 21±2 y; mean±SD]. METHODS: Training was performed on a cycle ergometer and involved a 2-min warm-up (50 W), 3 x 20-s ‘all-out’ bouts interspersed with 2-min of recovery (50 W), and a 3-min cool-down (50 W). VO2max was determined using a ramp test to exhaustion. Qmax was subsequently determined using inert gas rebreathing (Innocor) over a 2-min period of exercise performed at 90% of the peak work rate attained during the VO2max test. Pilot testing confirmed this protocol elicited VO2max over the 2-min period of Qmax measurement. The performance test was a 2 kJ/kg body weight cycling time trial. All measurements were performed twice at baseline, and reproducibility determined as a coefficient of variation (CV). The CV for VO2max, Qmax and time trial performance was 5.8, 4.7 and 4.2%, respectively. Pre- and post-training measurements were compared using a paired t-test. RESULTS: VO2max increased after SIT from 37.0±7.3 to 40.7±8.3 ml/kg/min (p<0.001), but Qmax was unchanged (17.2±3.8 vs 17.7±4.6 L/min; p>0.05). Exercise performance improved after SIT from 1040±247 to 938±238 s (p<0.001). Absolute VO2max was positively correlated with Qmax (r2 = 0.86, p < 0.001). CONCLUSION: Six sessions of SIT increased VO2max without changing Qmax in previously untrained individuals. These data support previous suggestions that the early increase in VO2max after SIT may be due mainly to peripheral responses (i.e., enhanced oxygen extraction by skeletal muscle), rather than a central change in blood oxygen delivery. Supported by NSERC

Contribution of oxygen extraction fraction to maximal oxygen uptake in healthy young men.

We analysed the importance of systemic and peripheral arteriovenous O2 difference ( a-v¯O2 difference and a‐vfO2 difference, respectively) and O2 extraction fraction for maximal oxygen uptake ( V˙O2max). Fick law of diffusion and the Piiper and Scheid model were applied to investigate whether diffusion versus perfusion limitations vary with V˙O2max. Articles (n = 17) publishing individual data (n = 154) on V˙O2max, maximal cardiac output ( Q˙max; indicator‐dilution or the Fick method), a-v¯O2 difference (catheters or the Fick equation) and systemic O2 extraction fraction were identified. For the peripheral responses, group‐mean data (articles: n = 27; subjects: n = 234) on leg blood flow (LBF; thermodilution), a‐vfO2 difference and O2 extraction fraction (arterial and femoral venous catheters) were obtained. Q˙max and two‐LBF increased linearly by 4.9‐6.0 L · min–1 per 1 L · min–1 increase in V˙O2max (R 2 = .73 and R 2 = .67, respectively; both P < .001). The a-v¯O2 difference increased from 118‐168 mL · L–1 from a V˙O2max of 2‐4.5 L · min–1 followed by a reduction (second‐order polynomial: R 2 = .27). After accounting for a hypoxemia‐induced decrease in arterial O2 content with increasing V˙O2max (R 2 = .17; P < .001), systemic O2 extraction fraction increased up to ~90% ( V˙O2max: 4.5 L · min–1) with no further change (exponential decay model: R 2 = .42). Likewise, leg O2 extraction fraction increased with V˙O2max to approach a maximal value of ~90‐95% (R 2 = .83). Muscle O2 diffusing capacity and the equilibration index Y increased linearly with V˙O2max (R 2 = .77 and R 2 = .31, respectively; both P < .01), reflecting decreasing O2 diffusional limitations and accentuating O2 delivery limitations. In conclusion, although O2 delivery is the main limiting factor to V˙O2max, enhanced O2 extraction fraction (≥90%) contributes to the remarkably high V˙O2max in endurance‐trained individuals.

The Menopause Alters Aerobic Adaptations to High-Intensity Interval Training.

Postmenopausal women have lower resting cardiac function than premenopausal women, but whether the menopause influences maximal cardiac output and hence exercise capacity is unclear. It is possible that premenopausal and postmenopausal women achieve similar improvements in maximal aerobic capacity (V˙O2max) and cardiac output with exercise training via different regional left ventricular muscle function ("LV mechanics"), as suggested by in vitro and animal studies. The aim of this study was to investigate the effects of the menopause on LV mechanics and adaptations to exercise training. Twenty-five healthy untrained middle-age women (age, 45-58 yr; 11 premenopausal, 14 postmenopausal) completed 12 wk of exercise training. Before and after exercise training, (i) V˙O2max and blood volume were determined, and (ii) LV mechanics were assessed using echocardiography at rest and during two submaximal physiological tests - lower-body negative pressure and supine cycling. The increase in V˙O2max after exercise training was 9% smaller in postmenopausal than premenopausal women, concomitant with a smaller increase in blood volume (P < 0.05). However, cardiac output and LV volumes were not different between premenopausal and postmenopausal women (P > 0.05) despite altered regional LV muscle function, as indicated by higher basal mechanics in premenopausal women during the physiological tests after exercise training (P < 0.05). These findings are the first to confirm altered LV mechanics in postmenopausal women. In addition, the reduced aerobic adaptability to exercise training in postmenopausal women does not appear to be a central cardiac limitation and may be due to altered blood volume distribution and lower peripheral adaptations.

Appropriate heart rate during exercise in Fontan patients.

To evaluate heart rate against workload and oxygen consumption during exercise in Fontan patients. Fontan patients (n = 27) and healthy controls (n = 25) underwent cardiopulmonary exercise testing with linear increase of load. Heart rate and oxygen uptake were measured during tests. Heart rate recovery was recorded for 10 minutes. Heart rate at midpoint (140 ± 14 versus 153 ± 11, p < 0.001) and at maximal effort (171 ± 14 versus 191 ± 10 beats per minute, p < 0.001) of test was lower for patients than controls. Heart rate recovery was similar between groups. Heart rate in relation to workload was higher for patients than controls both at midpoint and maximal effort. Heart rate in relation to oxygen uptake was similar between groups throughout test. Oxygen pulse, an indirect surrogate measure of stroke volume, was reduced at maximal effort in patients compared to controls (6.6 ± 1.1 versus 7.5 ± 1.4 ml·beat-1·m-2, p < 0.05) and increased significantly less from midpoint to maximal effort for patients than controls (p < 0.05). Heart rate is increased in relation to workload in Fontan patients compared with controls. At higher loads, Fontan patients seem to have reduced heart rate and smaller increase in oxygen pulse, which may be explained by inability to further increase stroke volume and cardiac output. Reduced ability to increase or maintain stroke volume at higher heart rates may be an important limiting factor for maximal cardiac output, oxygen uptake, and physical performance.

Multilevel allometric modelling of maximum cardiac output, maximum arteriovenous oxygen difference, and peak oxygen uptake in 11\u201313-year-olds

PurposesTo investigate longitudinally (1) the contribution of morphological covariates to explaining the development of maximum cardiac output ({dot{text{Q}}} max) and maximum arteriovenous oxygen difference (a-vO2 diff max), (2) sex differences in {dot{text{Q}}} max and a-vO2 diff max once age, maturity status, and morphological covariates have been controlled for, and, (3) the contribution of concurrent changes in morphological and cardiovascular covariates to explaining the sex-specific development of peak oxygen uptake (dot{{V}}{mathrm{O}}_{2}).MethodsFifty-one (32 boys) 11–13-year-olds had their peak dot{{V}}{mathrm{O}}_{2}, maximum heart rate (HR max), {dot{text{Q}}} max, and a-vO2 diff max determined during treadmill running on three annual occasions. The data were analysed using multilevel allometric modelling.ResultsThere were no sex differences in HR max which was not significantly (p > 0.05) correlated with age, morphological variables, or peak dot{{V}}{mathrm{O}}_{2}. The best-fit models for {dot{text{Q}}} max and a-vO2 diff max were with fat-free mass (FFM) as covariate with age, maturity status, and haemoglobin concentration not significant (p > 0.05). FFM was the dominant influence on the development of peak dot{{V}}{mathrm{O}}_{2}. With FFM controlled for, the introduction of either {dot{text{Q}}} max or a-vO2 diff max to multilevel models of peak dot{{V}}{mathrm{O}}_{2} resulted in significant (p < 0.05) additional contributions to explaining the sex difference.Conclusions(1) With FFM controlled for, there were no sex differences in {dot{text{Q}}} max or a-vO2 diff max, (2) FFM was the dominant influence on the development of peak dot{{V}}{mathrm{O}}_{2}, and (3) with FFM and either {dot{text{Q}}} max or a-vO2 diff max controlled for, there remained an unresolved sex difference of ~ 4% in peak dot{{V}}{mathrm{O}}_{2} .