Blunted Cardiac Output from Overtraining Is Related to Increased Arterial Stiffness

Acute effects of static stretching exercise-induced decrease in arterial stiffness on maximal aerobic capacity

BACKGROUND

We recently have reported that individual day-to-day arterial stiffness variations are associated with maximal aerobic capacity. However, the evidence of this phenomenon was not provided sufficiently. The present study aimed to examine whether a decrease in arterial stiffness through static stretching exercise could enhance maximal aerobic capacity.

METHODS

Twelve healthy young men (age 22±2 years, mean and standard deviation) participated in this study and underwent two separate sessions in a randomized controlled crossover design: a single session of a whole-body static stretching exercise protocol that involved the trunk, upper limb, and lower limb (stretch condition), and sedentary control where they rested in the exercise room. Brachial-ankle pulse wave velocity (baPWV) was measured as an index of systemic arterial stiffness before, immediately after and at 30 min after both conditions. Maximal oxygen uptake (V̇O2max) was assessed using a graded power test on an electronically braked cycle ergometer after these measurements.

RESULTS

As we expected, there was a significant decrease in the baPWV at 30 min after the stretch trial compared to baseline values (P=0.01). The baPWV in the stretch condition was lower than that of the control condition, while V̇O2max in the stretch condition was higher than that of the control condition (P=0.03).

CONCLUSIONS

Based on these findings, it can be inferred that an acute reduction in arterial stiffness may contribute to change in maximal aerobic capacity.

Monitoring fatigue state with heart rate-based and subjective methods during intensified training in recreational runners

The purpose of this study was firstly to examine the sensitivity of heart rate (HR)-based and subjective monitoring markers to intensified endurance training; and secondly, to investigate the validity of these markers to distinguish individuals in different fatigue states. A total of 24 recreational runners performed a 3-week baseline period, a 2-week overload period, and a 1-week recovery period. Performance was assessed before and after each period with a 3000m running test. Recovery was monitored with daily orthostatic tests, nocturnal HR recordings, questionnaires, and exercise data. The participants were divided into subgroups (overreached/OR, n = 8; responders/RESP, n = 12) based on the changes in performance and subjective recovery. The responses to the second week of the overload period were compared between the subgroups. RESP improved their baseline 3000 m time (p < 0.001) after the overload period (-2.5 ± 1.0%), and the change differed (p < 0.001) from OR (0.6 ± 1.2%). The changes in nocturnal HR (OR 3.2 ± 3.1%; RESP -2.8 ± 3.7%, p = 0.002) and HR variability (OR -0.7 ± 1.8%; RESP 2.1 ± 1.6%, p = 0.011) differed between the subgroups. In addition, the decrease in subjective readiness to train (p = 0.009) and increase in soreness of the legs (p = 0.04) were greater in OR compared to RESP. Nocturnal HR, readiness to train, and exercise-derived HR-running power index had ≥85% positive and negative predictive values in the discrimination between OR and RESP individuals. In conclusion, exercise tolerance can vary substantially in recreational runners. The results supported the usefulness of nocturnal HR and subjective recovery assessments in recognizing fatigue states.

Altered carbohydrate oxidation during exercise in overreached endurance athletes is applicable to training monitoring with continuous glucose monitors

PURPOSE

The purpose of the study was to investigate whether carbohydrate utilization is altered during exercise in overreached endurance athletes and examine the utility of continuous glucose monitors (CGM) to detect overreaching status.

METHODS

Eleven endurance athletes (M:8, F:3) completed a 5-week training block consisting of 1 week of reduced training (PRE), 3 weeks of high-intensity overload training (POST), and 1 week of recovery training (REC). Participants completed a Lamberts and Lambert Submaximal Cycling Test (LSCT) and 5 km time-trial at PRE, POST, and REC time points, 15 min following the ingestion of a 50 g glucose beverage with glucose recorded each minute via CGM.

RESULTS

Performance in the 5 km time-trial was reduced at POST (∆-7 ± 10 W, p = 0.04,η p 2  = 0.35) and improved at REC (∆12 ± 9 W from PRE, p = 0.01,η p 2  = 0.66), with reductions in peak lactate (∆-3.0 ± 2.0 mmol/L, p = 0.001,η p 2  = 0.71), peak HR (∆-6 ± 3 bpm, p < 0.001,η p 2  = 0.86), and Hooper-Mackinnon well-being scores (∆10 ± 5 a.u., p < 0.001,η p 2  = 0.79), indicating athletes were functionally overreached. The respiratory exchange ratio was suppressed at POST relative to REC during the 60% (POST: 0.80 ± 0.05, REC: 0.87 ± 0.05, p < 0.001,η p 2  = 0.74), and 80% (POST: 0.93 ± 0.05, REC: 1.00 ± 0.05, p = 0.003,η p 2  = 0.68) of HR-matched submaximal stages of the LSCT. CGM glucose was reduced during HR-matched submaximal exercise in the LSCT at POST (p = 0.047,η p 2  = 0.36), but not the 5 km time-trial (p = 0.07,η p 2  = 0.28) in overreached athletes.

CONCLUSION

This preliminary investigation demonstrates a reduction in CGM-derived glucose and carbohydrate oxidation during submaximal exercise in overreached athletes. The use of CGM during submaximal exercise following standardized nutrition could be employed as a monitoring tool to detect overreaching in endurance athletes.

A Simple Model for Diagnosis of Maladaptations to Exercise Training

Background

The concept of overreaching and super compensation is widely in use by athletes and coaches seeking to maximize performance and adaptations to exercise training. The physiological aspects of acute fatigue, overreaching and non-functional overreaching are, however, not well understood, and well-defined negative physiological outcomes are missing. Instead, the concept relies heavily on performance outcomes for differentiating between the states. Recent advancements in the field of integrated exercise physiology have associated maladaptations in muscular oxidative function to high loads of exercise training.

Method

Eleven female and male subjects that exercised regularly but did not engage in high-intensity interval training (HIIT) were recruited to a 4-week long training intervention where the responses to different training loads were studied. Highly monitored HIIT sessions were performed on a cycle ergometer in a progressive fashion with the intent to accomplish a training overload. Throughout the intervention, physiological and psychological responses to HIIT were assessed, and the results were used to construct a diagnostic model that could indicate maladaptations during excessive training loads.

Results

We here use mitochondrial function as an early marker of excessive training loads and show the dynamic responses of several physiological and psychological measurements during different training loads. During HIIT, a loss of mitochondrial function was associated with reduced glycolytic, glucoregulatory and heart rate responses and increased ratings of perceived exertion in relation to several physiological measurements. The profile of mood states was highly affected after excessive training loads, whereas performance staled rather than decreased. By implementing five of the most affected and relevant measured parameters in a diagnostic model, we could successfully, and in all the subjects, identify the training loads that lead to maladaptations.

Conclusions

As mitochondrial parameters cannot be assessed without donating a muscle biopsy, this test can be used by coaches and exercise physiologists to monitor adaptation to exercise training for improving performance and optimizing the health benefits of exercise.

Clinical trial registry numberNCT04753021. Retrospectively registered 2021-02-12.

Considerations for Sex-Cognizant Research in Exercise Biology and Medicine

As the fields of kinesiology, exercise science, and human movement developed, the majority of the research focused on male physiology and extrapolated findings to females. In the medical sphere, basing practice on data developed in only males resulted in the removal of drugs from the market in the late 1990s due to severe side effects (some life-threatening) in females that were not observed in males. In response to substantial evidence demonstrating exercise-induced health benefits, exercise is often promoted as a key modality in disease prevention, management, and rehabilitation. However, much like the early days of drug development, a historical literature knowledge base of predominantly male studies may leave the exercise field vulnerable to overlooking potentially key biological differences in males and females that may be important to consider in prescribing exercise (e.g., how exercise responses may differ between sexes and whether there are optimal approaches to consider for females that differ from conventional approaches that are based on male physiology). Thus, this review will discuss anatomical, physiological, and skeletal muscle molecular differences that may contribute to sex differences in exercise responses, as well as clinical considerations based on this knowledge in athletic and general populations over the continuum of age. Finally, this review summarizes the current gaps in knowledge, highlights the areas ripe for future research, and considerations for sex-cognizant research in exercise fields.

Differences between Elite Male and Female Badminton Athletes Regarding Heart Rate Variability, Arterial Stiffness, and Aerobic Capacity

Cardiovascular health and aerobic capacity play crucial roles in determining the performance of athletes in the highly competitive sport of badminton. Few studies have directly compared heart rate variability (HRV), arterial stiffness, and aerobic capacity between male and female athletes, especially among badminton athletes. This study investigated sex differences in HRV, arterial stiffness, and aerobic capacity in badminton athletes. Elite badminton athletes were recruited and divided into male (n = 20, 21.0 ± 1.8 years old) and female (n = 16, 21.2 ± 2.3 years old) groups. Both groups performed an incremental treadmill running test for the evaluation of maximal oxygen consumption (V.O2max), anaerobic threshold, and time to exhaustion. They started exercising at a treadmill speed of 2.7 km/h and an inclination of 10% gradient for 3 min, and the speed and inclination were gradually increased every 3 min until they were exhausted or fatigued volitionally. HRV was examined using the Polar heart rate monitor over a period of 5 min at rest in the supine position. Subsequently, the index of arterial stiffness was examined under the same condition. Our results revealed significant differences between the male and female athletes in V.O2max (men: 60.38 ± 8.98 mL/kg/min, women: 48.13 ± 7.72 mL/kg/min, p < 0.05), anaerobic threshold (men: 41.50 ± 7.26 mL/kg/min, women: 32.51 ± 6.19 mL/kg/min, p < 0.05), time to exhaustion (men: 902.15 ± 120.15 s, women: 780.56 ± 67.63 s, p < 0.05), systolic blood pressure (men: 125.27 ± 7.76 mmHg, women: 107.16 ± 11.09 mmHg, p < 0.05), and arterial stiffness index (men: 63.56 ± 12.55, women: 53.83 ± 8.03, p < 0.05). However, no significant differences in HRV measures were observed between the two groups. These findings suggested that the male badminton athletes demonstrated significantly higher aerobic capacity than did the female athletes, but there were no significant differences in HRV measures. The female athletes exhibited superior arterial function, compared with their male counterparts.

Effects of Recurring IPC vs. rIPC Maneuvers on Exercise Performance, Pulse Wave Velocity, and Red Blood Cell Deformability: Special Consideration of Reflow Varieties

Beneficial effects of (remote) ischemia preconditioning ((r)IPC), short episodes of blood occlusion and reperfusion, are well-characterized, but there is no consensus regarding the effectiveness of (r)IPC on exercise performance. Additionally, direct comparisons of IPC and rIPC but also differences between reflow modes, low reflow (LR) and high reflow (HR) in particular, are lacking, which were thus the aims of this study. Thirty healthy males conducted a performance test before and after five consecutive days with either IPC or rIPC maneuvers (n = 15 per group). This procedure was repeated after a two-week wash-out phase to test for both reflow conditions in random order. Results revealed improved exercise parameters in the IPC LR and to a lesser extent in the rIPC LR intervention. RBC deformability increased during both rIPC LR and IPC LR, respectively. Pulse wave velocity (PWV) and blood pressures remained unaltered. In general, deformability and PWV positively correlated with performance parameters. In conclusion, occlusion of small areas seems insufficient to affect large remote muscle groups. The reflow condition might influence the effectiveness of the (r)IPC intervention, which might in part explain the inconsistent findings of previous investigations. Future studies should now focus on the underlying mechanisms to explain this finding.

Endurance and Sprint Training Improve Glycemia and V˙O2peak but only Frequent Endurance Benefits Blood Pressure and Lipidemia

PURPOSE

Sprint interval training (SIT) has gained popularity as a time-effective alternative to moderate-intensity endurance training (END). However, whether SIT is equally effective for decreasing cardiometabolic risk factors remains debatable, as many beneficial effects of exercise are thought to be transient, and unlike END, SIT is not recommended daily. Therefore, in line with current exercise recommendations, we examined the ability of SIT and END to improve cardiometabolic health in overweight/obese males.

METHODS

Twenty-three participants were randomized to perform 6 wk of constant workload SIT (3 d·wk-1, 4-6 × 30 s ~170% Wpeak, 2 min recovery, n = 12) or END (5 d·wk-1, 30-40 min, ~60% Wpeak, n = 11) on cycle ergometers. Aerobic capacity (V˙O2peak), body composition, blood pressure (BP), arterial stiffness, endothelial function, glucose and lipid tolerance, and free-living glycemic regulation were assessed pre- and posttraining.

RESULTS

Both END and SIT increased V˙O2peak (END ~15%, SIT ~5%) and glucose tolerance (~20%). However, only END decreased diastolic BP, abdominal fat, and improved postprandial lipid tolerance, representing improvements in cardiovascular risk factors that did not occur after SIT. Although SIT, but not END, increased endothelial function, arterial stiffness was not altered in either group. Indices of free-living glycemic regulation were improved after END and trended toward an improvement after SIT (P = 0.06-0.09). However, glycemic control was better on exercise compared with rest days, highlighting the importance of exercise frequency. Furthermore, in an exploratory nature, favorable individual responses (V˙O2peak, BP, glucose tolerance, lipidemia, and body fat) were more prevalent after END than low-frequency SIT.

CONCLUSION

As only high-frequency END improved BP and lipid tolerance, free-living glycemic regulation was better on days that participants exercised, and favorable individual responses were consistent after END, high-frequency END may favorably improve cardiometabolic health.

Functional Overreaching in Endurance Athletes: A Necessity or Cause for Concern?

There are variable responses to short-term periods of increased training load in endurance athletes, whereby some athletes improve without deleterious effects on performance, while others show diminished exercise performance for a period of days to months. The time course of the decrement in performance and subsequent restoration, or super compensation, has been used to distinguish between the different stages of the fitness-fatigue adaptive continuum termed functional overreaching (FOR), non-functional overreaching (NFOR) or overtraining syndrome. The short-term transient training-induced decrements in performance elicited by increases in training load (i.e. FOR) are thought be a sufficient and necessary component of a training program and are often deliberately induced in training to promote meaningful physiological adaptations and performance super-compensation. Despite the supposition that deliberately inducing FOR in athletes may be necessary to achieve performance super-compensation, FOR has been associated with various negative cardiovascular, hormonal and metabolic consequences. Furthermore, recent studies have demonstrated dampened training and performance adaptations in FOR athletes compared to non-overreached athletes who completed the same training program or the same relative increase in training load. However, this is not always the case and a number of studies have also demonstrated substantial performance super-compensation in athletes who were classified as being FOR. It is possible that there are a number of contextual factors that may influence the metabolic consequences associated with FOR and classifying this training-induced state of fatigue based purely on a decrement in performance may be an oversimplification. Here, the most recent research on FOR in endurance athletes will be critically evaluated to determine (1) if there is sufficient evidence to indicate that inducing a state of FOR is necessary and required to induce a performance super-compensation; (2) the metabolic consequences that are associated with FOR; (3) strategies that may prevent the negative consequences of overreaching.

Improved Carotid Elasticity but Altered Central Hemodynamics and Carotid Structure in Young Athletes

Young athletes most often exceed the physical activity recommendations of the World Health Organization. Therefore, they are of special interest for investigating cardiovascular adaptions to exercise. This study aimed to examine the arterial structure and function of young athletes 12-17 years old and compare these parameters to reference values of healthy cohorts. Carotid intima-media thickness (cIMT), carotid diameter, cIMT÷carotid diameter-ratio (cIDR), arterial compliance (AC), elastic modulus (Ep), β stiffness index (β), and carotid pulse wave velocity (PWVβ) were determined using ultrasound in 331 young athletes (77 girls; mean age, 14.6 ± 1.30 years). Central systolic blood pressure (cSBP) and aortic PWV (aPWV) were measured using the oscillometric device Mobil-O-Graph. Standard deviation scores (SDS) of all parameters were calculated according to German reference values. The 75th and 90th percentiles were defined as the threshold for elevated cIMT and arterial stiffness, respectively. Activity behavior was assessed with the MoMo physical activity questionnaire, and maximum power output with a standard cardiopulmonary exercise test. One-sample t-tests were performed to investigate the significant deviations in SDS values compared to the value "0". All subjects participated in competitive sports for at least 6 h per week (565.6 ± 206.0 min/week). Of the 331 young athletes, 135 (40.2%) had cIMT >75th percentile, 71 (21.5%) had cSBP >90th percentile, and 94 (28.4%) had aPWV>90th percentile. We observed higher cIMT SDS (p < 0.001), cIDR SDS (p = 0.009), and AC SDS (p < 0.001) but lower β SDS (p < 0.001), Ep SDS (p < 0.001), and PWVβ SDS (p < 0.001) compared to the reference cohort. The cSBP SDS (p < 0.001) and aPWV SDS (p < 0.001) were elevated. In conclusion, cIMT and cIDR were higher in young athletes than in a reference cohort. Furthermore, young athletes presented better carotid elasticity and lower arterial stiffness of the carotid artery. However, central arterial stiffness was higher compared to the reference cohort. The thickening of the carotid intima-media complex in combination with a reduction in arterial stiffness indicates a physiological adaptation to exercise in youth.

Vascular Function Is Differentially Altered by Distance after Prolonged Running

PURPOSE

Ultraendurance exercise is steadily growing in popularity; however, the effect of increasingly prolonged durations of exercise on the vascular endothelium is unknown. The aim of this study was to characterize the effect of various ultramarathon running distances on vascular form and function.

METHODS

We evaluated vascular endothelial function via flow-mediated dilation (FMD) in the superficial femoral artery, as well as microvascular function, inflammatory factors, and central artery stiffness, before and after participants completed 25-km (7M:2F), 50-km (11M:10F), 80-km (9M:4F), or 160-km (9M:2F) trail races all run on the same day and course.

RESULTS

Completion required 149 ± 20, 386 ± 111, 704 ± 130, and 1470 ± 235 min, with corresponding average paces of 6.0 ± 0.8, 7.7 ± 2.2, 8.6 ± 1.3, and 9.6 ± 1.3 min·km-1, respectively. At baseline, there were no differences in participant characteristics across race distance groups. Shear rate stimulus trended toward an increase after the race (P = 0.07), but resting postrace artery diameter (P < 0.001) was elevated to a similar extent in all conditions. There was a reduction in FMD after the 50-km race (Δ -1.9% ± 2.2%, P < 0.01), but not the 25-km (Δ +0.3% ± 2.9%, P = 0.8), the 80-km (Δ -1.5% ± 3.2%, P = 0.1), or the 160-km (Δ +0.5% ± 2.5%, P = 0.5) race. Inflammatory markers increased most after 160 km, but arterial stiffness and microvascular function were not differently affected by race distance.

CONCLUSIONS

Although the superficial femoral artery baseline diameter was larger postexercise regardless of race distance, only the 50-km race reduced FMD, whereas a short-duration higher-intensity race (25 km) and longer-duration lower-intensity races (160 km) did not. Therefore, a 50-km ultramarathon may represent the intersection between higher-intensity exercise over a prolonged duration, causing reduced endothelial function not seen in shorter or longer distances.

Arterial Stiffness and Left Ventricular Diastolic Function in Endurance Athletes

The present study investigated the relationship between arterial stiffness and left ventricular diastolic function in endurance-trained athletes. Sixteen young male endurance-trained athletes and nine sedentary of similar age men participated in this study. Resting measures in carotid-femoral pulse wave velocity were obtained to assess arterial stiffness. Left ventricular diastolic function was assessed using 2-dimensional echocardiography. The athletes tended to have lower arterial stiffness than the controls (P=0.071). Transmitral A-waves in the athletes were significantly lower (P=0.018) than the controls, and left ventricular mass (P=0.034), transmitral E-wave/A-wave (P=0.005) and peak early diastolic mitral annular velocity at the septal site (P=0.005) in the athletes were significantly greater than the controls. A significant correlation was found between arterial stiffness and left ventricular diastolic function (E-wave: r=- 0.682, P=0.003, E-wave/A-wave: r=- 0.712, P=0.002, peak early diastolic mitral annular velocity at the septal site: r=- 0.557, P=0.025) in the athletes, whereas no correlation was found in controls. These results suggest that lower arterial stiffness is associated with higher left ventricular diastolic function in endurance-trained athletes.

In vitro ketone-supported mitochondrial respiration is minimal when other substrates are readily available in cardiac and skeletal muscle

KEY POINTS

Ketone bodies are proposed to represent an alternative fuel source driving energy production, particularly during exercise. Biologically, the extent to which mitochondria utilize ketone bodies compared to other substrates remains unknown. We demonstrate in vitro that maximal mitochondrial respiration supported by ketone bodies is low when compared to carbohydrate-derived substrates in the left ventricle and red gastrocnemius muscle from rodents, and in human skeletal muscle. When considering intramuscular concentrations of ketone bodies and the presence of other carbohydrate and lipid substrates, biological rates of mitochondrial respiration supported by ketone bodies are predicted to be minimal. At the mitochondrial level, it is therefore unlikely that ketone bodies are an important source for energy production in cardiac and skeletal muscle, particularly when other substrates are readily available.

ABSTRACT

Ketone bodies (KB) have recently gained popularity as an alternative fuel source to support mitochondrial oxidative phosphorylation and enhance exercise performance. However, given the low activity of ketolytic enzymes and potential inhibition from carbohydrate oxidation, it remains unknown if KBs can contribute to energy production. We therefore determined the ability of KBs (sodium dl-β-hydroxybutyrate, β-HB; lithium acetoacetate, AcAc) to stimulate in vitro mitochondrial respiration in the left ventricle (LV) and red gastrocnemius (RG) of rats, and in human vastus lateralis. Compared to pyruvate, the ability of KBs to maximally drive respiration was low in isolated mitochondria and permeabilized fibres (PmFb) from the LV (∼30-35% of pyruvate), RG (∼10-30%), and human vastus lateralis (∼2-10%). In PmFb, the concentration of KBs required to half-maximally drive respiration (LV: 889 µm β-HB, 801 µm AcAc; RG: 782 µm β-HB, 267 µm AcAc) were greater than KB content representative of the muscle microenvironment (∼100 µm). This would predict low rates (∼1-4% of pyruvate) of biological KB-supported respiration in the LV (8-14 pmol s^-1 mg^-1 ) and RG (3-6 pmol s^-1 mg^-1 ) at rest and following exercise. Moreover, KBs did not increase respiration in the presence of saturating pyruvate, submaximal pyruvate (100 µm) reduced the ability of physiological β-HB to drive respiration, and addition of other intracellular substrates (succinate + palmitoylcarnitine) decreased maximal KB-supported respiration. As a result, product inhibition is likely to limit KB oxidation. Altogether, the ability of KBs to drive mitochondrial respiration is minimal and they are likely to be outcompeted by other substrates, compromising their use as an important energy source.

Defective autophagy in vascular smooth muscle cells increases passive stiffness of the mouse aortic vessel wall

Aging and associated progressive arterial stiffening are both important predictors for the development of cardiovascular diseases. Recent evidence showed that autophagy, a catabolic cellular mechanism responsible for nutrient recycling, plays a major role in the physiology of vascular cells such as endothelial cells and vascular smooth muscle cells (VSMCs). Moreover, several autophagy inducing compounds are effective in treating arterial stiffness. Yet, a direct link between VSMC autophagy and arterial stiffness remains largely unidentified. Therefore, we investigated the effects of a VSMC-specific deletion of the essential autophagy-related gene Atg7 in young mice (3.5 months) (Atg7^F/F SM22α-Cre⁺ mice) on the biomechanical properties of the aorta, using an in-house developed Rodent Oscillatory Tension Set-up to study Arterial Compliance (ROTSAC). Aortic segments of Atg7^F/F SM22α-Cre⁺ mice displayed attenuated compliance and higher arterial stiffness, which was more evident at higher distention pressures. Passive aortic wall remodeling, rather than differences in VSMC tone, is responsible for these phenomena, since differences in compliance and stiffness between Atg7^+/+ SM22α-Cre⁺ and Atg7^F/F SM22α-Cre⁺ aortas were more pronounced when VSMCs were completely relaxed by the addition of exogenous nitric oxide. These observations are supported by histological data showing a 13% increase in medial wall thickness and a 14% decrease in elastin along with elevated elastin fragmentation. In addition, expression of the calcium-binding protein S100A4, which is linked to matrix remodeling, was elevated in aortic segments of Atg7^F/F SM22α-Cre⁺ mice. Overall, these findings illustrate that autophagy exerts a crucial role in defining arterial wall compliance.

Cardiac remodeling after six weeks of high-intensity interval training to exhaustion in endurance-trained men

High-intensity interval training (HIIT) improves physical performance of endurance athletes, although studies examining its cardiovascular effects are sparse. We evaluated the impact of HIIT on blood pressure, heart rate, and cardiac cavities' size and function in endurance-trained adults. Seventeen endurance-trained men underwent 24-h ambulatory blood pressure monitoring and Doppler echocardiography at baseline and after 6 wk of HIIT. Participants were divided into 2 groups [85% maximal aerobic power (HIIT₈₅), n = 8 and 115% maximal aerobic power (HIIT₁₁₅), n = 9] to compare the impact of different HIIT intensities. Ambulatory blood pressure monitoring and cardiac chambers' size and function were similar between groups at baseline. HIIT reduced heart rate (55 ± 8 vs. 51 ± 7 beats/min; P = 0.003), systolic blood pressure (121 ± 11 vs. 118 ± 9 mmHg; P = 0.01), mean arterial pressure (90 ± 8 vs. 89 ± 6 mmHg; P = 0.03), and pulse pressure (52 ± 6 vs. 49 ± 5 mmHg; P = 0.01) irrespective of training intensity. Left atrium volumes increased after HIIT (maximal: 50 ± 14 vs. 54 ± 14 mL; P = 0.02; minimal: 15 ± 5 vs. 20 ± 8 mL; P = 0.01) in both groups. Right ventricle global longitudinal strain lowered after training in the HIIT₈₅ group only (20 ± 4 vs. 17 ± 3%, P = 0.04). In endurance-trained men, 6 wk of HIIT reduced systolic blood pressure and mean arterial pressure and increased left atrium volumes irrespective of training intensity, whereas submaximal HIIT deteriorated right ventricle systolic function.NEW & NOTEWORTHY The novel findings of this study are that 6 wk of high-intensity interval training increases left atrial volumes irrespective of training intensity (85 or 115% maximal aerobic power), whereas the submaximal training decreases right ventricular systolic function in endurance-trained men. These results may help identify the exercise threshold for potential toxicity of intense exercise training for at-risk individuals and ideal exercise training regimens conferring optimal cardiovascular protection and adapted endurance training for athletes.