High-intensity Endurance Training Research Articles

Endurance Training Improves Leg Proton Release and Decreases Potassium Release During High-Intensity Exercise in Normoxia and Hypobaric Hypoxia.

To assess the impact of endurance training on skeletal muscle release of H+ and K+. Nine participants performed one-legged knee extension endurance training at moderate and high intensities (70%-85% of Wpeak), three to four sessions·week-1 for 6 weeks. Post-training, the trained and untrained (control) leg performed two-legged knee extension at low, moderate, and high intensities (40%, 62%, and 83% of Wpeak) in normoxia and hypoxia (~4000 m). The legs were exercised simultaneously to ensure identical arterial inflow concentrations of ions and metabolites, and identical power output was controlled by visual feedback. Leg blood flow was measured (ultrasound Doppler), and acid-base variables, lactate- and K+ concentrations were assessed in arterial and femoral venous blood to study K+ and H+ release. Ion transporter abundances were assessed in muscle biopsies. Lactate-dependent H+ release was similar in hypoxia to normoxia (p = 0.168) and was lower in the trained than the control leg at low-moderate intensities (p = 0.060-0.006) but similar during high-intensity exercise. Lactate-independent and total H+ releases were higher in hypoxia (p < 0.05) and increased more with power output in the trained leg (leg-by-power output interactions: p = 0.02). K+ release was similar at low intensity but lower in the trained leg during high-intensity exercise in normoxia (p = 0.024) and hypoxia (p = 0.007). The trained leg had higher abundances of Na+/H+ exchanger 1 (p = 0.047) and Na+/K+ pump subunit α (p = 0.036). Moderate- to high-intensity endurance training increases lactate-independent H+ release and reduces K+ release during high-intensity exercise, coinciding with increased Na+/H+ exchanger 1 and Na+/K+ pump subunit α muscle abundances.

Endurance Training Improves Leg Proton Release and Decreases Potassium Release During High-Intensity Exercise in Normoxia and Hypobaric Hypoxia.

To assess the impact of endurance training on skeletal muscle release of H+ and K+. Nine participants performed one-legged knee extension endurance training at moderate and high intensities (70%-85% of Wpeak), three to four sessions·week-1 for 6 weeks. Post-training, the trained and untrained (control) leg performed two-legged knee extension at low, moderate, and high intensities (40%, 62%, and 83% of Wpeak) in normoxia and hypoxia (~4000 m). The legs were exercised simultaneously to ensure identical arterial inflow concentrations of ions and metabolites, and identical power output was controlled by visual feedback. Leg blood flow was measured (ultrasound Doppler), and acid-base variables, lactate- and K+ concentrations were assessed in arterial and femoral venous blood to study K+ and H+ release. Ion transporter abundances were assessed in muscle biopsies. Lactate-dependent H+ release was similar in hypoxia to normoxia (p = 0.168) and was lower in the trained than the control leg at low-moderate intensities (p = 0.060-0.006) but similar during high-intensity exercise. Lactate-independent and total H+ releases were higher in hypoxia (p < 0.05) and increased more with power output in the trained leg (leg-by-power output interactions: p = 0.02). K+ release was similar at low intensity but lower in the trained leg during high-intensity exercise in normoxia (p = 0.024) and hypoxia (p = 0.007). The trained leg had higher abundances of Na+/H+ exchanger 1 (p = 0.047) and Na+/K+ pump subunit α (p = 0.036). Moderate- to high-intensity endurance training increases lactate-independent H+ release and reduces K+ release during high-intensity exercise, coinciding with increased Na+/H+ exchanger 1 and Na+/K+ pump subunit α muscle abundances.

The Impact of Normobaric Hypoxia and Intermittent Hypoxic Training on Cardiac Biomarkers in Endurance Athletes: A Pilot Study.

This study explores the effects of normobaric hypoxia and intermittent hypoxic training (IHT) on the physiological condition of the cardiac muscle in swimmers. Hypoxia has been reported to elicit both beneficial and adverse changes in the cardiovascular system, but its impact on the myocardium during acute exercise and altitude/hypoxic training remains less understood. We aimed to determine how a single bout of intense interval exercise and a four-week period of high-intensity endurance training under normobaric hypoxia affect cardiac marker activity in swimmers. Sixteen young male swimmers were divided into two groups: one undergoing training in hypoxia and the other in normoxia. Cardiac markers, including troponin I and T (cTnI and cTnT), heart-type fatty acid-binding protein (H-FABP), creatine kinase-MB isoenzyme (CK-MB), and myoglobin (Mb), were analyzed to assess the myocardium's response. We found no significant differences in the physiological response of the cardiac muscle to intense physical exertion between hypoxia and normoxia. Four weeks of IHT did not alter the resting levels of cTnT, cTnI, and H-FABP, but it resulted in a noteworthy decrease in the resting concentration of CK-MB, suggesting enhanced cardiac muscle adaptation to exercise. In contrast, a reduction in resting Mb levels was observed in the control group training in normoxia. These findings suggest that IHT at moderate altitudes does not adversely affect cardiac muscle condition and may support cardiac muscle adaptation, affirming the safety and efficacy of IHT as a training method for athletes.

Evaluation of the effect of Exercise Trainings and CGRP receptor antagonist (BIBN 4096) on mitochondrial dynamic in the hippocampus of male Wistar rats

BackgroundExercise training showed beneficial effects on brain. The purpose of the present study is to evaluate the effect of six weeks of high-intensity interval training (HIIT) and Endurance training (ET) with calcitonin gene-related peptide (CGRP) receptor antagonist on the expression of genes involved in mitochondrial dynamics and apoptosis in hippocampal tissue of male Wistar rats. MethodsIn this study, forty-two healthymale Wistar rats (8-week) were randomly divided into 6 groups (n = 7) as follow; 1) Control; 2) HIIT which performed 6 weeks of HIIT; 3) ET which performed 6 weeks of endurance training; 4) CGRPi received 10 mg/kg CGRP receptor antagonist every day at the last 2 weeks; 5) CGRPi-HIIT performed HIIT and received CGRP receptor antagonist; 6) CGRPi-ET performed ET and received CGRP receptor antagonist. Real-time PCR (2-ΔΔCT) and western blotting were employedto measure the expression of genes and protein, respectively. ResultsHIIT and ET significantly increased Bcl-2, Pgc-1α, Sirt3, and Nrf-1 gene expression in the hippocampal tissue (p < 0.05, p < 0.01, p < 0.01, and p < 0.001, respectively). ET-CGRPi and HIIT-CGRPi significantly increased Sirt3, Pgc-1α, and Nrf-1 gene expression compared to the control group (p < 0.05, p < 0.01, and p < 0.05, respectively). ConclusionET and HIIT-induced physiological alterations in the hippocampus. In fact, this modulation showed protective properties in the hippocampusvia up regulation of Bcl-2, Pgc-1α, Nrf-1, and Sirt3 gene expression. CGRPi did not cause gene or protein changes harmful to mitochondrial dynamic balance and apoptosis in the hippocampus of rats.

‘Effects of a home-based bimodal lifestyle intervention in frail patients with end-stage liver disease awaiting orthotopic liver transplantation’: study protocol of a non-randomised clinical trial

IntroductionPatients with end-stage liver disease awaiting orthotopic liver transplantation (OLT) are generally classified as frail due to disease-related malnutrition and a progressive decline in musculoskeletal and aerobic fitness, which is...

Assessing the cardiac autonomic response to bicycle exercise in Olympic athletes with different loads of endurance training: new insights from statistical indicators based on multilevel exploratory factor analysis.

Aim: The mechanisms governing the organism's response to exercise are complex and difficult to study. Spectral analysis of heart rate variability (HRV) could represent a convenient methodology for studying humans' autonomic nervous system (ANS). However, difficulties in interpreting the multitude of correlated HRV-derived indices, mainly when computed over different time segments, may represent a barrier to its usage. This preliminary investigation addressed to elite athletes proposes a novel method describing the cardiac autonomic response to exercise based on multilevel exploratory factor analysis (MEFA), which reduces the multitude of HRV-derived indices to fewer uncorrelated ANS indicators capable of accounting for their interrelationships and overcoming the above difficulties. Methods: The study involved 30 Italian Olympic athletes, divided into 15 cyclists (prevalent high-intensity endurance training) and 15 shooters (prevalent technical training with low-intensity endurance component). All athletes underwent a complete test of a dynamic protocol, constituted by a rest-stand test followed by a stepwise bicycle stress test subdivided into a single bout of progressive endurance (from aerobic to anaerobic) exercise and recovery. Then, by spectral analysis, values of 12 ANS proxies were computed at each time segment (9 epochs in all) of the complete test. Results: We obtained two global ANS indicators (amplitude and frequency), expressing the athletes' overall autonomic response to the complete test, and three dynamic ANS indicators (amplitude, signal self-similarity, and oscillatory), describing the principal dynamics over time of the variability of RR interval (RRV). Globally, cyclists have significantly higher amplitude levels (median ± MAD: cyclists 69.9 ± 20.5; shooters 37.2 ± 19.4) and lower frequency levels (median ± MAD: cyclists 37.4 ± 14.8; shooters 78.2 ± 10.2) than shooters, i.e., a parasympathetic predominance compared to shooters. Regarding the RRV dynamics, the signal self-similarity and oscillatory indicators have the strongest sensitivity in detecting the rest-stand change; the amplitude indicator is highly effective in detecting the athletes' autonomic changes in the exercise fraction; the amplitude and oscillatory indicators present significant differences between cyclists and shooters in specific test epochs. Conclusion: This MEFA application permits a more straightforward representation of the complexity characterizing ANS modulation during exercise, simplifying the interpretation of the HRV-derived indices and facilitating the possible real-life use of this non-invasive methodology.

SAT100 Management Of Post-exercise Hyperglycemia In A Patient Using Control IQ Artificial Pancreas System - A Case Report

Abstract Disclosure: P. Sharma: None. A. Ramirez Berlioz: None. Introduction: The automated insulin delivery (AID) Tandem Control IQ (CIQ) system has improved glycemic control with increased time in range (∼10%) &amp; decreased hypoglycemic events (∼1%) through automatic basal rate modifications &amp; correction bolus administration. The sleep &amp; exercise activity (EA) decrease hypoglycemia risk. The CIQ EA decreases basal rate for predicted glucose =&amp;lt;140 mg/dl, increases basal rate for predicted glucose &amp;gt;160 mg/dl, and suspends insulin delivery for glucose =&amp;lt;80 mg/dl. It is designed for mild-moderate physical activity and is aggressive for high-intensity aerobic exercise or endurance training. High-intensity activity can cause post-exercise hyperglycemia. There is minimal data regarding management of post-exercise hyperglycemia when using AID systems. Case Report: A 40 year old female with uncomplicated type 1 diabetes mellitus managed by Tandem CIQ system reported post-exercise hyperglycemia after starting a new exercise routine. Previous routine included cardio and weight training on 4 days of the week. She had recently started a stationary cycling routine lasting 15-45 minutes with varying intensity. She would start the CIQ EA 1.5 hours prior to exercise and stop after completion. The pump report revealed hyperglycemia between 200-300 mg/dl occurring within 1 hour after exercise, lasting several hours after. Patient attempted using normal mode during exercise, manual bolusing immediately after exercise, and post-exercise insulin sensitivity factor modification without effect. Stopping EA 10-15 mins before completion led to elimination of post-exercise hyperglycemia. Discussion: The CIQ EA is designed to decrease exercise-induced hypoglycemia. After high-intensity exercise, the CIQ algorithm can exaggerate the hyperglycemia. High-intensity routines such as sprints, weight-lifting, intensive cycling, are associated with varying degrees of hyperglycemia. Our patient's new cycling routine was higher-intensity compared to what she previously did, leading to persistent hyperglycemia. Some recommendations to avoid post-exercise hyperglycemia in patients on AID systems include using CIQ normal mode during exercise, utilization of a temporary basal rate, or administration of a manual correction bolus. However, the use of normal mode or temporary basal rates can lead to glycemic variations during exercise. A manual correction bolus administered after exercise may be too late to avoid the hyperglycemia and leads to subsequent hypoglycemia due to enhanced insulin sensitivity post-activity. We tried stopping EA a few minutes before routine completion and found that 10 minutes was appropriate. We suggest that discontinuation of the EA 10 minutes before completion of exercise routine can alleviate post-exercise hyperglycemia. Additional studies are required to confirm whether this method would work on a larger scale. Presentation: Saturday, June 17, 2023

Effect of High-Intensity Resistance Training Versus Endurance Training on Irisin and Adipomyokine Levels in Healthy Individuals: An 8-Week Interventional Study.

Background: Irisin and adipomyokine are proteins secreted by the body during exercise and exhibit potential therapeutic effects for chronic disorders. Gaining insights into how high-intensity resistance training and endurance training influence irisin and adipomyokine secretion could shed light on optimizing exercise regimens for potential therapeutic applications. Such knowledge could pave the way for personalized exercise prescriptions and contribute to the development of novel treatments for chronic conditions, enhancing overall health and well-being. Objectives: To investigate the effects of high-intensity resistance training (HIRT) and endurance training on irisin and adipomyokine levels in healthy individuals. Methods: An 8-week interventional comparative study was conducted at Nimra Institute of Medical Sciences, Andhra Pradesh, India. One hundred healthy male individuals aged 21 to 35 were divided into two groups: HIRT and endurance. The HIRT group performed high-intensity resistance training, while the endurance group performed endurance training. Ethical approval was obtained, and baseline and post-intervention values of the participants were recorded and analyzed using SPSS software. Results: After 8 weeks, irisin levels were significantly elevated in the HIRT group (167.39±11.27) compared to the endurance group (155.39±11.28). A positive correlation was observed between skeletal muscle and irisin levels in both the HIRT group (χ2-16.38; p=0.04) and the endurance group (χ2-18.36; p=0.01). Additionally, TNF-α (HIRT: 81.47±4.02 and Endurance: 61.19±4.00) and interleukin-6 (IL-6) (HIRT: 46.84±4.46 and Endurance: 36.15±3.89) levels significantly increased in the HIRT group. However, there was no significant change in leptin levels in either group (HIRT: 3.75±0.58 0.58 and 4.15±0.58). Conclusion: The findings of this study indicate that HIRTis more effective in increasing irisin levels compared to endurance training. However, the notable elevation of IL-6and TNF-α in the HIRT group raises concerns about potential chronic inflammation. To optimize outcomes, a combined approach, coupling HIRT and endurance training, may be beneficial. Additionally, the results emphasize the significance of skeletal muscle as a primary source of irisin secretion, implying that increased muscle contraction contributes to higher irisin release even in healthy individuals. These insights can guide exercise prescriptions and potentially enhance therapeutic strategies for chronic disorders.

Moderate- and High-Intensity Endurance Training Alleviate Diabetes-Induced Cardiac Dysfunction in Rats.

Exercise training is an encouraging approach to treat cardiac dysfunction in type 2 diabetes (T2DM), but the impact of its intensity is not understood. We aim to investigate whether and, if so, how moderate-intensity training (MIT) and high-intensity interval training (HIIT) alleviate adverse cardiac remodeling and dysfunction in rats with T2DM. Male rats received standard chow (n = 10) or Western diet (WD) to induce T2DM. Hereafter, WD rats were subjected to a 12-week sedentary lifestyle (n = 8), running MIT (n = 7) or HIIT (n = 7). Insulin resistance and glucose tolerance were assessed during the oral glucose tolerance test. Plasma advanced glycation end-products (AGEs) were evaluated. Echocardiography and hemodynamic measurements evaluated cardiac function. Underlying cardiac mechanisms were investigated by histology, western blot and colorimetry. We found that MIT and HIIT lowered insulin resistance and blood glucose levels compared to sedentary WD rats. MIT decreased harmful plasma AGE levels. In the heart, MIT and HIIT lowered end-diastolic pressure, left ventricular wall thickness and interstitial collagen deposition. Cardiac citrate synthase activity, mitochondrial oxidative capacity marker, raised after both exercise training modalities. We conclude that MIT and HIIT are effective in alleviating diastolic dysfunction and pathological cardiac remodeling in T2DM, by lowering fibrosis and optimizing mitochondrial capacity.

Durability is improved by both low and high intensity endurance training.

Introduction: This is one of the first intervention studies to examine how low- (LIT) and high-intensity endurance training (HIT) affect durability, defined as 'time of onset and magnitude of deterioration in physiological-profiling characteristics over time during prolonged exercise'. Methods: Sedentary and recreationally active men (n = 16) and women (n = 19) completed either LIT (average weekly training time 6.8 0.7h) or HIT (1.6 0.2h) cycling for 10 weeks. Durability was analyzed before and after the training period from three factors during 3-h cycling at 48% of pretraining maximal oxygen uptake (VO2max): 1) by the magnitude and 2) onset of drifts (i.e. gradual change in energy expenditure, heart rate, rate of perceived exertion, ventilation, left ventricular ejection time, and stroke volume), 3) by the 'physiological strain', defined to be the absolute responses of heart rate and its variability, lactate, and rate of perceived exertion. Results: When all three factors were averaged the durability was improved similarly (time x group p = 0.42) in both groups (LIT: p = 0.03, g = 0.49; HIT: p = 0.01, g = 0.62). In the LIT group, magnitude of average of drifts and their onset did not reach statistically significance level of p < 0.05 (magnitude: 7.7 6.8% vs. 6.3 6.0%, p = 0.09, g = 0.27; onset: 106 57min vs. 131 59 min, p = 0.08, g = 0.58), while averaged physiological strain improved (p = 0.01, g = 0.60). In HIT, both magnitude and onset decreased (magnitude: 8.8 7.9% vs. 5.4 6.7%, p = 0.03, g = 0.49; onset: 108 54min vs. 137 57 min, p = 0.03, g = 0.61), and physiological strain improved (p = 0.005, g = 0.78). VO2max increased only after HIT (time x group p < 0.001, g = 1.51). Conclusion: Durability improved similarly by both LIT and HIT based on reduced physiological drifts, their postponed onsets, and changes in physiological strain. Despite durability enhanced among untrained people, a 10-week intervention did not alter drifts and their onsets in a large amount, even though it attenuated physiological strain.

Effectiveness of a 3-Week Rehabilitation Program Combining Muscle Strengthening and Endurance Exercises Prior to Total Knee Arthroplasty: A Non-Randomized Controlled Trial

We evaluated the effectiveness of a high-intensity preoperative resistance and endurance training program in improving physical function among patients scheduled for total knee arthroplasty. This non-randomized controlled trial included 33 knee osteoarthritis patients scheduled to undergo total knee arthroplasty at a tertiary public medical university hospital. Fourteen and nineteen patients were non-randomly assigned to intervention and control groups, respectively. All patients underwent total knee arthroplasty and a postoperative rehabilitation program. The intervention group participated in a preoperative rehabilitation program comprising high-intensity resistance and endurance training exercises to increase lower limb muscle strength and endurance capacity. The control group received only exercise instruction. The primary outcome was the 6-min walking distance, which was significantly higher in the intervention group (399 ± 59.8 m) than in the control group (348 ± 75.1 m) 3 months post-surgery. There were no significant differences between the groups 3 months post-surgery in muscle strength, visual analog scale, WOMAC-Pain, range of motion of knee flexion, and extension. A 3-week preoperative rehabilitation program combining muscle strengthening and endurance training improved endurance 3 months after total knee arthroplasty. Thus, preoperative rehabilitation is important for improving postoperative activity.

Endurance Training with Moderate and Intense Intensity Along with the Consumption of Safflower Extract Improved the Oxidative Damage of Testicular Tissue Caused by Dexamethasone in Adult Male Rats

Background: Chronic use of dexamethasone, especially in athletes, is associated with reproductive disorders. Objectives: This study aimed to investigate the effect of high and moderate intensity endurance training along with the consumption of safflower extract on testicular oxidative damage and testosterone level in male rats treated with dexamethasone. Methods: A total of 45 male Wistar rats were divided into the controlled and treated groups. Dexamethasone was subcutaneously injected for five days at a dose of 8 mg/kg. High and moderate intensity exercises were performed for ten weeks (five days a week) at speeds of 28 and 34 m/min, respectively, on the treadmill. The safflower seed extract (500 mg/kg of the body weight) was administered daily during the training period by gavage. At the end of the given period, testicular tissue sampling was performed to measure malondialdehyde, total antioxidant capacity, Nrf2, and testosterone levels. Results: The results showed that high and moderate intensity exercises along with the consumption of safflower seed extract (P = 0.000) as well as high intensity exercise alone (P = 0.04) caused a significant increase in Nrf2 expression in animals receiving dexamethasone compared to the dexamethasone group. No significant change was observed in the testosterone level of the dexamethasone group compared to that of the control group. However, a significant change was detected in its level in some groups treated with moderate exercise, intense exercise, and safflower extract. Conclusions: It was concluded that moderate and high intensity endurance training, along with the consumption of safflower extract, had the potential to prevent infertility caused by dexamethasone.

Intensity demands and peak performance of elite soccer referees during match play.

This study examined the peak physical and physiological (heart rate) performance intensities andassociated decrements in elite soccer referees during match play. Longitudinal study. Physical performancevariables and heart rate were analyzed during 457 matches across two seasons. Differences between halves, and the rate ofdecline in peak performance intensities across moving average durations of 1-10 minutes were assessed using linear mixed models and power-law analysis, respectively. Large significant differences were observed between halves for mean total distance, mean velocity, mean heart rate, and percentage of maximal heart rate (p ≤ 0.05; r = 0.51-0.64). Peak intensities (p ≤ 0.05; r = 0.15-0.17) and the rate of decline (p < 0.001; r = 0.17-0.37) were significantly higher in the 2nd half compared to the 1st half, for relative total distance, relative high-intensity running and mean velocity. The rate of decline was significantly greater in the 2nd half than the 1st half for relative distance covered by high-intensity acceleration (>2 m/s-2/min), deceleration (<-2 m/s-2/min), and relative mean heart rate (p < 0.001; r = 0.28-0.61). Elite soccer referees might have experienced transient fatigue during match play, as relative high-intensity running immediately following the most intense 5-minute period significantly declined by 61.2% ( p< 0.001; r = 0.94), and was 16.2% lower than the mean 5-minute period (p < 0.001; r = 0.34). Increased physical and physiological demands during match play, with associated declines in the second half and transient signs of fatigue throughout the match, supports the inclusion of high-intensity interval and endurance training programs to prepare soccer referees for the intensity demands and peak performance outcomes of match play.

Effect of High-Intensity Strength and Endurance Training in the Form of Small Circuits on Changes in Lipid Levels in Men Aged 35-40 Years.

Background: Blood lipid profiles consist of total cholesterol (TC) and its fractions, high-density lipoprotein cholesterol (HDL), low-density lipoprotein cholesterol (LDL), non-high-density lipoprotein cholesterol (non-HDL), and triglycerides (TG). For several decades, studies have examined the effects of various factors on lipid status and its association with the risk of developing arteriosclerosis and cardiovascular disease. The beneficial effects of increased physical activity on cardiovascular health have been demonstrated by appropriate modulation of lipid profiles. For individuals with low physical activity, the literature recommends engaging in various forms of training that can improve physical fitness and resting lipid status. The aim of the study was to examine whether a specific original training program improves lipid profiles to the levels recommended for the male population. Methods: The study involved two equal (n = 15) groups of men (experimental and control groups, aged 35–40 years). The experimental group performed 60-min training sessions for 8 weeks (3 times a week) including a set of strength and endurance exercises. Before and after the training program, blood was drawn from both groups for serum determination of TC, HDL, LDL non-HDL, and TG, and a battery of four field physical performance tests was administered. Results: Statistically significant decreases (TC by 19.3%, TG by 23.7%, LDL by 15%), a non-significant decrease (10% for non-HDL), and no change for HDL were found in the experimental group. Control group showed a statistically significant decrease, by 7.4% for TC. The results confirm the effectiveness of the proposed training in improving health indices. Conclusions: The 8-week training program met the health-related fitness paradigm recommended for physical activity in men aged 35–40 years. After the completion of the program, all the participants expressed their satisfaction from participating in a health-promoting experiment.

Exploring Moderators of the Effect of High vs. Low-to-Moderate Intensity Exercise on Cardiorespiratory Fitness During Breast Cancer Treatment - Analyses of a Subsample From the Phys-Can RCT.

IntroductionThe results from the physical training and cancer randomized controlled trial (Phys-Can RCT) indicate that high intensity (HI) strength and endurance training during (neo-)adjuvant cancer treatment is more beneficial for cardiorespiratory fitness (CRF, measured as peak oxygen uptake [VO2peak]) than low-to-moderate intensity (LMI) exercise. Adherence to the exercise intervention and demographic or clinical characteristics of patients with breast cancer undergoing adjuvant treatment may moderate the exercise intervention effect on VO2peak. In this study, the objective was to investigate whether baseline values of VO2peak, body mass index (BMI), time spent in moderate- to vigorous-intensity physical activity (MVPA), physical fatigue, age, chemotherapy treatment, and the adherence to the endurance training moderated the effect of HI vs. LMI exercise on VO2peak.Materials and MethodsWe used data collected from a subsample from the Phys-Can RCT; women who were diagnosed with breast cancer and had a valid baseline and post-intervention VO2peak test were included (n = 255). The exercise interventions from the RCT included strength and endurance training at either LMI, which was continuous endurance training at 40–50% of heart rate reserve (HRR), or at HI, which was interval training at 80–90% of HRR, with similar exercise volume in the two groups. Linear regression analyses were used to investigate moderating effects using a significance level of p < 0.10. Statistically significant interactions were examined further using the Johnson–Neyman (J-N) technique and regions of significance (for continuous variables) or box plots with adjusted means of post-intervention VO2peak (for binary variables).ResultsAge, as a continuous variable, and adherence, dichotomized into < or > 58% based on median, moderated the effect of HI vs. LMI on CRF (B = −0.08, 95% CI [−0.16, 0.01], pinteraction = 0.06, and B = 1.63, 95% CI [−0.12, 3.38], pinteraction = 0.07, respectively). The J-N technique and regions of significance indicated that the intervention effect (HI vs. LMI) was positive and statistically significant in participants aged 61 years or older. Baseline measurement of CRF, MVPA, BMI, physical fatigue, and chemotherapy treatment did not significantly moderate the intervention effect on CRF.ConclusionWomen with breast cancer who are older and who have higher adherence to the exercise regimen may have larger effects of HI exercise during (neo-)adjuvant cancer treatment on CRF.

Cardiac remodeling accompanied by increased arrhythmia susceptibility in a dog model of chronic high-intensity endurance training

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): This work was supported by NKFIH grants (K-19992, K-135464) and GINOP-2.3.2-15-2016-00047. Background Despite the cardiovascular benefits of regular physical exercise, chronic high-level exercise can evoke malignant arrhythmias, including ventricular fibrillation and even sudden cardiac death, especially in young top athletes. In some cases the underlying mechanisms are unclear. Objectives The goal of this study was to assess mechanisms underlying cardiac structural-electrical changes and arrhythmia vulnerability by high-level vigorous exercise training in animal species that are electrophysiologically relevant to the human heart. Methods Beagle dogs were randomly assigned to matched sedentary (Sed) or intensive exercise-training (Ex) groups (n=12-12). Ex dogs underwent a 4-month-long intensive treadmill-running protocol (5 days a week, 6 hours a day at a speed of 14-21 km/h with an inclination from 5% to 12%). In vivo echocardiography and electrophysiological measurements were performed. Proarrhythmic sensitivity was tested and the autonomic alterations were examined. At study end, arrhythmia susceptibility was tested with high-frequency burst stimulation in open-chest anaesthetized dogs. This was followed by cardiac excision and cardiomyocyte isolation, formalin preservation for histology, snap-freezing in liquid nitrogen for molecular biology. Results The vigorous endurance training was resulted in increased left ventricular end-diastolic diameter, increased septal wall thickness and greater left ventricular mass index (Ex vs. Sed: 98±12 vs. 136±7 g/m2, p&amp;lt;0.05). Some degree of enhanced fibrosis was observed. Endurance training decreased heart rate both in whole animal and in vitro dog experiments. ECG recordings presented enhanced heart rate variability parameters, prolonged PQ (Ex vs. Sed: 98.3±2.9 vs. 116.7±3.6 ms, p&amp;lt;0.05), QRS (Ex vs. Sed : 60.5±2.4 vs 70.8±1.6 ms, p&amp;lt;0.05), QTc (Ex vs. Sed: 213.6±2.8 vs. 237.1±3.4 ms, p&amp;lt;0.05), Tp-Te (Ex vs. Sed: 27.9±2.5 vs.36.5±1.7 ms, p&amp;lt;0.05) intervals associated with significantly enhanced QT interval variability (eg. Ex vs. Sed: QT-STV, 2.5±0.2 vs. 3.6±0.4 ms, p&amp;lt;0.05), reflecting elevated level of repolarization dispersion. Ectopic activity was also enhanced in the exercised dog ventricle. Atropine treatment resulted in moderate heart rate increase in the Ex animals. Chronic endurance exercise elevated the proarrhythmic risk and consequent ventricular fibrillation in dogs subjected to burst electrical stimulation. Conclusion We developed a new animal model that shares similarities with the human endurance-trained athlete’s heart. The model represents increased arrhythmia susceptibility, an important clinical paradigm, and explores potential underlying mechanisms, including vagal enhancement, increased repolarization dispersion and enhanced fibrotic changes. Increased arrhythmia susceptibility is supported by the enhanced arrhythmia incidence in the exercised group. Similar changes may be present in young human top athletes, however further investigations are required.

Response to Endurance Training Using Critical Speed: Influence of Genetic Background and Exercise Intensity

Exercise is used as a therapeutic option to improve an individual's quality of life or as a method to attenuate the severity of cardiovascular, respiratory, or metabolic‐related diseases. However, changes in cardiorespiratory fitness in response to endurance training are often heterogenous with individuals being more or less responsive to a similar exercise protocol. Heterogeneity in responses to exercise training is observed in humans and rodents. Low responses to training might be mitigated by modifying the standard exercise training protocol by altering the frequency, intensity, or duration of training. Threshold‐based exercise training prescription, e.g., critical speed, has also been proposed as a means to reduce the variability of training responses. The aim of this study was to identify the effect of different exercise training intensities on changes in exercise capacity in two inbred strains of mice, NZW/LacJ (NZW) and FVB/NJ (FVB). NZW mice were selected because they respond poorly to moderate intensity endurance exercise whereas, FVB mice respond well to endurance training. We hypothesized that increasing the intensity of the training would reduce the number of low or non‐responding NZW mice. To test this hypothesis, female mice from each strain were assigned to one of three treadmill training groups based on critical speed (CS): 80% of their critical speed (CS80%), 90% of their critical speed (CS90%), or sedentary controls (SED). Exercise groups within each strain were volume matched and thus ran the same distance over the 6‐week training period. Pre‐training exercise capacity differed between NZW (30.5 ± 3.5 min) and FVB (36.1 ± 2.8 min) mice (P &lt; 0.001). Critical speeds also differed between strains (NZW: 25.1 ± 2.4 m/min; FVB: 32.9 ± 1.6 m/min, P &lt; 0.001). After training, both FVB exercise groups, CS80% (10.0 ± 4.9 min, P = 0.004) and CS90% (14.0 ± 7.7 min, P = 0.007), improved their endurance capacity. In contrast, NZW CS80% did not significantly improve after training (0.4 ± 4.6 min), but NZW CS90% improved significantly (3.6 ± 2.7 min, P = 0.02). Collectively, these data indicate that the high‐responder FVB strain can adapt to moderate‐intensity and high‐intensity endurance training. The low‐responder NZW strain only showed significant improvement after sufficient homeostatic stress was induced through high‐intensity endurance training. These data suggest that increasing exercise intensity can improve responses to exercise training in low‐ or non‐responding mice.

How Do the Effects of an 8-Week Intervention Influence Subsequent Performance Development in Cross-Country Skiers?

To investigate how the effects of increased low- versus high-intensity endurance training in an 8-week intervention influenced the subsequent development of performance and physiological indices in cross-country skiers. Forty-four (32 men and 12 women) junior cross-country skiers were randomly assigned into a low-intensity training group (LITG, n = 20) or high-intensity training group (HITG, n = 24) for an 8-week intervention followed by 5 weeks of standardized training with similar intensity distribution, and thereafter 14 weeks of self-chosen training. Performance and physiological indices in running and in roller-ski skating were determined preintervention, after the intervention, and after the standardized training period. Roller-ski skating was also tested after the period of self-chosen training. No between-groups changes from preintervention to after the standardized training period were found in peak speed when incremental running and roller-ski skating (P = .83 and .51), although performance in both modes was improved in the LITG (2.4% [4.6%] and 3.3% [3.3%], P < .05) and in roller-ski skating for HITG (2.6% [3.1%], P < .01). While improvements in maximal oxygen consumption running and peak oxygen uptake roller-ski skating were greater in HITG than in LITG from preintervention to after the intervention, no between-groups differences were found from preintervention to after the standardized training period (P = .50 and .46), although peak oxygen uptake in roller-ski skating significantly improved in HITG (5.7% [7.0%], P < .01). No changes either within or between groups were found after the period of self-chosen training. Differences in adaptations elicited by a short-term intervention focusing on low- versus high-intensity endurance training had little or no effect on the subsequent development of performance or physiological indices following a period of standardized training in cross-country skiers.

Effects of Increased Load of Low- Versus High-Intensity Endurance Training on Performance and Physiological Adaptations in Endurance Athletes.

To compare the effects of increased load of low- versus high-intensity endurance training on performance and physiological adaptations in well-trained endurance athletes. Following an 8-week preintervention period, 51 (36 men and 15 women) junior cross-country skiers and biathletes were randomly allocated into a low-intensity (LIG, n = 26) or high-intensity training group (HIG, n = 25) for an 8-week intervention period, load balanced using the overall training impulse score. Both groups performed an uphill running time trial and were assessed for laboratory performance and physiological profiling in treadmill running and roller-ski skating preintervention and postintervention. Preintervention to postintervention changes in running time trial did not differ between groups (P = .44), with significant improvements in HIG (-2.3% [3.2%], P = .01) but not in LIG (-1.5% [2.9%], P = .20). There were no differences between groups in peak speed changes when incremental running and roller-ski skating to exhaustion (P = .30 and P = .20, respectively), with both modes being significantly improved in HIG (2.2% [3.1%] and 2.5% [3.4%], both P < .01) and in roller-ski skating for LIG (1.5% [2.4%], P < .01). There was a between-group difference in running maximal oxygen uptake changes (P = .04), tending to improve in HIG (3.0% [6.4%], P = .09) but not in LIG (-0.7% [4.6%], P = .25). Changes in roller-ski skating peak oxygen uptake differed between groups (P = .02), with significant improvements in HIG (3.6% [5.4%], P = .01) but not in LIG (-0.1% [0.17%], P = .62). There was no significant difference in performance adaptations between increased load of low- versus high-intensity training in well-trained endurance athletes, although both methods improved performance. However, increased load of high-intensity training elicited better maximal oxygen uptake adaptations compared to increased load of low-intensity training.

Effect of Pre-conditioning of Endurance Training with Different Intensities on Soleus Muscle Atrophy in a Period of Inactivity: The Role of PGC-1α4 Gene

Background: This study aimed to measure PGC-1α4 soleus muscle and to investigate the effect of endurance training pre-conditioning with different intensities on the atrophy response of the soleus muscle to a period of inactivity. Methods: In this experimental study, 24 male Wistar rats were randomly divided into equal groups of control (C), control inactivity (CI), high-intensity endurance training group (HE) (treadmill speed 30 km/h), and low-intensity endurance training (LE) (treadmill’s speed: 10 km/h). After two weeks of familiarization, the endurance training group ran on a treadmill for two weeks (five sessions each week). The animal’s lower limbs were then immobilized for seven days. Then the soleus muscle was extracted, and after weighting, the expression of the PGC-1α4 gene was measured using the real-time polymerase chain reaction (realtime PCR) technique. Data were analyzed using SPSS software, version 24. Results: The expression of the PGC-1α4 gene was significantly higher in the HE group than the CI group. However, compared to the C group, all groups with inactivity intervention showed significantly lower PGC-1α4 gene levels. The ratio of muscle mass to body weight in the C group was significantly higher than the LE and CI groups, and higher in the HE group than the CI group. Conclusion: Endurance training seems to be able to reduce the destructive effects of inactive atrophy. The higher intensity of these exercises was more effective, which was associated with increased expression of the PGC-1α4 gene.