Continuous Endurance Training Research Articles

Effects of Exercise Training on Mitochondrial and Capillary Growth in Human Skeletal Muscle: A Systematic Review and Meta-Regression.

Skeletal muscle mitochondria and capillaries are crucial for aerobic fitness, and suppressed levels are associated with chronic and age-related diseases. Currently, evidence-based exercise training recommendations to enhance these characteristics are limited. It is essential to explore how factors, such as fitness level, age, sex, and disease affect mitochondrial and capillary adaptations to different exercise stimuli. The main aim of this study was to compare the effects of low- or moderate intensity continuous endurance training (ET), high-intensity interval or continuous training (HIT), and sprint interval training (SIT) on changes in skeletal muscle mitochondrial content and capillarization. Secondarily, the effects on maximal oxygen consumption (VO2max), muscle fiber cross-sectional area, and fiber type proportion were investigated. A systematic literature search was conducted in PubMed, Web of Science, and SPORTDiscus databases, with no data restrictions, up to 2 February 2022. Exercise training intervention studies of ET, HIT, and SIT were included if they had baseline and follow-up measures of at least one marker of mitochondrial content or capillarization. In total, data from 5973 participants in 353 and 131 research articles were included for the mitochondrial and capillary quantitative synthesis of this review, respectively. Additionally, measures of VO2max, muscle fiber cross-sectional area, and fiber type proportion were extracted from these studies. After adjusting for relevant covariates, such as training frequency, number of intervention weeks, and initial fitness level, percentage increases in mitochondrial content in response to exercise training increased to a similar extent with ET (23 ± 5%), HIT (27 ± 5%), and SIT (27 ± 7%) (P > 0.138), and were not influenced by age, sex, menopause, disease, or the amount of muscle mass engaged. Higher training frequencies (6 > 4 > 2 sessions/week) were associated with larger increases in mitochondrial content. Per total hour of exercise, SIT was ~ 2.3 times more efficient in increasing mitochondrial content than HIT and ~ 3.9 times more efficient than ET, while HIT was ~ 1.7 times more efficient than ET. Capillaries per fiber increased similarly with ET (15 ± 3%), HIT (13 ± 4%) and SIT (10 ± 11%) (P = 0.556) after adjustments for number of intervention weeks and initial fitness level. Capillaries per mm2 only increased after ET (13 ± 3%) and HIT (7 ± 4%), with increases being larger after ET compared with HIT and SIT (P < 0.05). This difference coincided with increases in fiber cross-sectional area after ET (6.5 ± 3.5%), HIT (8.9 ± 4.9%), and SIT (11.9 ± 15.1%). Gains in capillarization occurred primarily in the early stages of training (< 4weeks) and were only observed in untrained to moderately trained participants. The proportion of type I muscle fibers remained unaltered by exercise training (P > 0.116), but ET and SIT exhibited opposing effects (P = 0.041). VO2max increased similarly with ET, HIT, and SIT, although HIT showed a tendency for greater improvement compared with both ET and SIT (P = 0.082), while SIT displayed the largest increase per hour of exercise. Higher training frequencies (6 > 4 > 2 sessions/week) were associated with larger increases in VO2max. Women displayed greater percentage gains in VO2max compared with men (P = 0.008). Generally, lower initial fitness levels were associated with greater percentage improvements in mitochondrial content, capillarization, and VO2max. SIT was particularly effective in improving mitochondrial content and VO2max in the early stages of training, while ET and HIT showed slower but steady improvements over a greater number of training weeks. The magnitude of change in mitochondrial content, capillarization, and VO2max to exercise training is largely determined by the initial fitness level, with greater changes observed in individuals with lower initial fitness. The ability to adapt to exercise training is maintained throughout life, irrespective of sex and presence of disease. While training load (volume × intensity) is a suitable predictor of changes in mitochondrial content and VO2max, this relationship is less clear for capillary adaptations.

Comparing the Impact of Continuous Endurance and High-intensity Interval Training on Cecal Butyrate and Propionate Levels in Diabetic Rats Induced by High-fat Diet

Background: Dysbiosis and metabolic disorders of the microbiota, often caused by an imbalance in the intestinal microbial composition, are significant issues linked to immobility, obesity, and diabetes. Physical exercise is recognized for its role in managing these symptoms by regulating the composition and metabolites of the intestinal microbiota, thereby improving gut health and overall metabolic function. Objectives: This study aimed to investigate and compare the effects of continuous endurance training (CET) and high-intensity interval training (HIIT) on two key cecal microbiota metabolites, butyrate and propionate, in diabetic rats. Methods: Forty-five male Wistar rats were made diabetic by a high-fat diet and were trained under CET and HIIT exercise protocols. Cecal tissue samples were taken from the rats to evaluate the effect of exercise, and the levels of two microbial metabolites, butyrate and propionate, were measured using the high-performance liquid chromatography (HPLC) method. Results: Among the exercise patterns studied, HIIT significantly improved the concentrations of butyrate and propionate, while CET showed no effect on these metabolites. Conclusions: Our findings suggest that, unlike CET, HIIT may effectively mitigate metabolic disturbances resulting from gut dysbiosis in diabetic patients. However, any definitive conclusion about the effects of CET and HIIT exercises on intestinal microbial metabolites necessitates further comprehensive tests on other metabolites and an examination of additional supporting evidence, such as changes in the composition of the intestinal microbiome.

Effects and neural mechanisms of different physical activity on major depressive disorder based on cerebral multimodality monitoring: a narrative review.

Major depressive disorder (MDD) is currently the most common psychiatric disorder in the world. It characterized by a high incidence of disease with the symptoms like depressed mood, slowed thinking, and reduced cognitive function. Without timely intervention, there is a 20-30% risk of conversion to treatment-resistant depression (TRD) and a high burden for the patient, family and society. Numerous studies have shown that physical activity (PA) is a non-pharmacological treatment that can significantly improve the mental status of patients with MDD and has positive effects on cognitive function, sleep status, and brain plasticity. However, the physiological and psychological effects of different types of PA on individuals vary, and the dosage profile of PA in improving symptoms in patients with MDD has not been elucidated. In most current studies of MDD, PA can be categorized as continuous endurance training (ECT), explosive interval training (EIT), resistance strength training (RST), and mind-body training (MBT), and the effects on patients' depressive symptoms, cognitive function, and sleep varied. Therefore, the present study was based on a narrative review and included a large number of existing studies to investigate the characteristics and differences in the effects of different PA interventions on MDD. The study also investigated the characteristics and differences of different PA interventions in MDD, and explained the neural mechanisms through the results of multimodal brain function monitoring, including the intracranial environment and brain structure. It aims to provide exercise prescription and theoretical reference for future research in neuroscience and clinical intervention in MDD.

Effects of five types of exercise on vascular function in postmenopausal women: a network meta-analysis and systematic review of 32 randomized controlled trials.

As women age, especially after menopause, cardiovascular disease (CVD) prevalence rises, posing a significant global health concern. Regular exercise can mitigate CVD risks by improving blood pressure and lipid levels in postmenopausal women. Yet, the optimal exercise modality for enhancing vascular structure and function in this demographic remains uncertain. This study aims to compare five exercise forms to discern the most effective interventions for reducing cardiovascular risk in postmenopausal women. The study searched PubMed, Web of Science, Cochrane, EBSCO, and Embase databases. It conducted a network meta-analysis (NMA) of randomized controlled trials (RCTs) on five exercise interventions: continuous endurance training (CET), interval training (INT), resistance training (RT), aerobic combined with resistance training (CT), and hybrid-type training (HYB). Outcome measures included carotid artery intima-media thickness (IMT), nitric oxide (NO), augmentation index (AIx), pulse wave velocity (PWV), and flow-mediated dilatation (FMD) of the brachial artery. Eligible studies were assessed for bias using the Cochrane tool. A frequentist random-effects NMA was employed to rank exercise effects, calculating standardized mean differences (SMDs) with 95% confidence intervals (CIs). The analysis of 32 studies (n = 1,427) indicates significant increases in FMD with CET, INT, RT, and HYB in postmenopausal women. Reductions in PWV were significant with CET, INT, RT, CT, and HYB. AIx decreased significantly with INT and HYB. CET, INT, and CT significantly increased NO levels. However, no significant reduction in IMT was observed. SUCRA probabilities show INT as most effective for increasing FMD, CT for reducing PWV, INT for decreasing AIx, CT for lowering IMT, and INT for increasing NO in postmenopausal women. The study demonstrates that CET, INT, RT, and HYB have a significant positive impact on FMD in postmenopausal women. Furthermore, all five forms of exercise significantly enhance PWV in this population. INT and HYB were found to have a significant positive effect on AIx in postmenopausal women, while CET, INT, and CT were found to significantly improve NO levels. For improving vascular function in postmenopausal women, it is recommended to prioritize INT and CT exercise modalities. On the other hand, as CET and RT were not ranked at the top of the Sucra value ranking in this study and were less effective than INT and CT as exercise interventions to improve vascular function in postmenopausal women, it is not recommended that CET and RT be considered the preferred exercise modality.

Small-Sided Games versus Continuous Endurance Training in Female Handball Players.

The main aim of the study was to compare the training methods of continuous endurance training versus handball small-sided games (SSGs) in female handball players during the preseason. Eighteen female handball players from a first league in the Czech Republic voluntarily participated in the study. They were divided into two groups (the SSG group [n = 9; age: 21.22 ± 3.03 years] and a running group (RG) [n = 9; age: 23.78 ± 3.77 years]). Both groups continued regular preseason training for six weeks. The SSG group played two small-sided games per week (a total of 12 games during the monitoring period) in their training sessions during the monitored six-week period. The RG ran twice per week, participating in continuous endurance training in the 12 training sessions during the monitored six-week period. Fitness tests (pretest/posttest) were performed prior to the six weeks of intervention and one week afterwards. The order of the fitness tests in sequence was as follows: 20-m and 30-m sprints, a Modified Agility T test (MAT), a Standing Long-Jump Test, ball-throwing velocity, and a Yo-Yo Intermittent Test level 1. In the SSG group, there was a significant improvement in the T test (p = 0.034), ball-throwing velocity (p = 0.019), and the Yo-Yo IR1 (p = 0.003) performance. The RG showed a significant improvement in the Standing Long-Jump Test (p = 0.049), ball-throwing velocity (p = 0.003), and the Yo-Yo IR1 (p = 0.003) performance. In conclusion, the SSGT method had a positive effect on female players' MAT, ball-throwing velocity and YoYo IR1 results, and the CERT method had a significant effect only on the YoYo IR1 results. Handball SSGs are a more suitable training method due to exercise specificity.

Unraveling the mystery of isocaloric endurance training - Influence of exercise modality, biological sex, and physical fitness

BackgroundA sedentary lifestyle with low energy expenditure (EE) is associated with chronic diseases and mortality. Barriers such as “lack of time” or “lack of motivation” are common reasons why physical exercise is neglected in the general population. To optimize EE in the time available, time-efficient but also enjoyable types of exercise are required. We therefore used an isocaloric approach to systematically investigate the effects of six different endurance exercise modalities on metabolic, mechanical, cardiorespiratory, and subjective variables in relation to biological sex and physical fitness. MethodsOut of 104, 92 healthy participants (21 recreationally trained and 18 trained females, 25 recreationally trained and 28 trained males) were subjected to physiological exercise testing to determine the exercise intensities for six exercise modalities, i.e., three different high-intensity interval training (HIIT) protocols (5 × 4 min, 15 × 1 min, 30 × 30 sec intervals), threshold (THR), speed endurance production (SEP), and low-intensity continuous endurance training (LIT). One of three HIIT sessions served as the reference for the subsequent isocaloric exercise modalities which were completed in randomized order. Metabolic and mechanical variables, i.e., EE during exercise, time to isocaloric EE (Tiso), relative and absolute fat contribution, post-exercise oxygen consumption (EPOC), mechanical energy, as well as cardiorespiratory and subjective variables, i.e., heart rate, oxygen uptake response, rating of perceived exertion, and enjoyment were assessed. Data were analyzed using a 6 × 2 × 2 repeated-measures ANOVA. ResultsAll three versions of HIIT and THR achieved the same EE during exercise for the same training duration. We found that LIT had a 1.6-fold (p < 0.001) and SEP a 1.3-fold (p < 0.001) longer Tiso compared to HIIT with no effects of biological sex (p = 0.42, pη2 = 0.01) or physical fitness (p = 0.09, pη2 = 0.04). There was a main effect of exercise modality on EPOC (p < 0.001, pη2 = 0.76) with highest values for HIIT 30 × 30 (p = 0.032) and lowest for LIT (p < 0.001). The highest relative and absolute amounts of fatty acids were measured during LIT (p < 0.001), and the lowest values were obtained during HIIT modalities. HIIT 30 × 30 was the most enjoyable version of HIIT (p = 0.007), while THR was the least enjoyable exercise modality (p = 0.008). ConclusionHIIT modalities are time-saving and enjoyable, regardless of sex and physical fitness. The results illustrate the relationship between exercise modality and metabolic, physiological, and subjective responses, and are thus of great interest to healthy individuals seeking time-saving and enjoyable exercise options.

Research on Intelligent Analysis of Healthy Training Progress of Teenage Sports Athletes Using Various Modalities

The study compared different training modalities, such as high-intensity interval training versus continuous endurance training, on selected health-related physical fitness, biochemical and haematological parameters of teenage players yielding similar mechanical work and training duration. A random sampling technique was employed and affirmed by the Ethical Committee of Sichuan Province, China. Forty-five teenage sports players aging 18–19 from Sichuan Province, China, were categorized into two experimental and one control group (n = 15) subjects. The groups were allocated separately to high-intensity interval training, continuous endurance training, and control group for a three-month physical exercise program. Each group’s training intensity was set based on the resting heart rate, to assess the effects on health-related physical fitness using fitness gram variables such as cardiovascular endurance, muscular endurance, and flexibility. Biochemical and haematological fasting blood samples were taken and tested at baseline and post three months of training. Detailed descriptive statistics were carried out for the interpretation of the data. All the statistical analysis was completed using the IBM SPSS 20. Paired t-test and one-way ANCOVA were used to evaluate the effect of two aerobic training methods, and to determine the exact difference between the groups, Scheffe’s post hoc test was employed. The result of the study shows that cardiovascular endurance in HIIT showed a better performance of (25.6%) than in C.E.T. (18.1%). Regarding muscular endurance, C.E.T. achieved 19.6% and HIIT 16.2%. For flexibility, HIIT improved by (6.5%) while C.E.T. (5.8%). Accordingly, the study revealed significant changes in teenage sports players’ health-related fitness, biochemical and haematological parameters.

Systematic Review and Meta-Analysis of Circulating Irisin Levels Following Endurance Training: Results of Continuous and Interval Training.

Irisin has been suggested as a helpful hormone for adverse metabolic conditions. However, the interaction between acute endurance exercises and irisin is still unclear. The purpose of this systematic review and meta-analysis was to determine the acute effect of endurance training, either continuous or interval training, on circulating irisin in healthy adults. Literature search was conducted in Web of Science, PubMed, Scopus and CINAHL until September 2022. Clinical trials measuring irisin levels following a single session of interval or continuous endurance training in healthy adults were eligible. Cohen's d effect size (95% confidence level), subgroup analyses and univariate meta-regression were calculated using a random-effects model. The procedures described by PRISMA were followed and the protocol was prospectively registered with PROSPERO (CRD 42021240971). Data of the 16 included studies comprising 412 individuals showed a significant increase following one session of continuous endurance training (d = 0.33, 95% CI: 0.20 to 0.46, p < 0.001), while interval training did not change circulating irisin (d = 0.16, 95% CI: -0.12 to 0.44, p = 0.202). Both subgroup and univariate meta-regression analyses showed non-significant differences in the change of circulating irisin comparing blood measurement, exercise mode or previous level of physical activity of the participants and circulating irisin at baseline, duration, or intensity of the exercise, respectively. Continuous method for endurance training increases circulating irisin in healthy adults, while studies measuring circulating irisin following interval training in healthy adults are still limited to be conclusive.

Effects of Concurrent Resistance and Endurance Training Using Continuous or Intermittent Protocols on Muscle Hypertrophy: Systematic Review With Meta-Analysis.

Monserdà-Vilaró, A, Balsalobre-Fernández, C, Hoffman, JR, Alix-Fages, C, and Jiménez, SL. Effects of concurrent resistance and endurance training using continuous or intermittent protocols on muscle hypertrophy: Systematic review with meta-analysis. J Strength Cond Res 37(3): 688-709, 2023-The purpose of this systematic review with meta-analysis was to explore the effects of concurrent resistance and endurance training (CT) incorporating continuous or intermittent endurance training (ET) on whole-muscle and type I and II muscle fiber hypertrophy compared with resistance training (RT) alone. Randomized and nonrandomized studies reporting changes in cross-sectional area at muscle fiber and whole-muscle levels after RT compared with CT were included. Searches for such studies were performed in Web of Science, PubMed, Scopus, SPORTDiscus, and CINAHL electronic databases. The data reported in the included studies were pooled in a random-effects meta-analysis of standardized mean differences (SMDs). Twenty-five studies were included. At the whole-muscle level, there were no significant differences for any comparison (SMD < 0.03). By contrast, RT induced greater type I and type II muscle fiber hypertrophy than CT when high-intensity interval training (HIIT) was incorporated alone (SMD > 0.33) or combined with continuous ET (SMD > 0.27), but not compared with CT incorporating only continuous ET (SMD < 0.16). The subgroup analyses of this systematic review and meta-analysis showed that RT induces greater muscle fiber hypertrophy than CT when HIIT is included. However, no CT affected whole-muscle hypertrophy compared with RT.

Prescribing and adjusting exercise training in chronic respiratory diseases – Expert-based practical recommendations

BackgroundInternational guidelines recommend endurance (ET) and strength training (ST) in patients with chronic respiratory diseases (CRDs), but only provide rough guidance on how to set the initial training load. This may unintentionally lead to practice variation and inadequate training load adjustments. This study aimed to develop practical recommendations on tailoring ET and ST based on practices from international experts from the field of exercise training in CRDs. Methods35 experts were invited to address a 64-item online survey about how they prescribe and adjust exercise training. ResultsCycling (97%) and walking (86%) were the most commonly implemented ET modalities. Continuous endurance training (CET, 83%) and interval endurance training (IET, 86%) were the frequently applied ET types. Criteria to prescribe IET instead of CET were: patients do not tolerate CET due to dyspnoea at the initial training session (79%), intense breathlessness during initial exercise assessment (76%), and/or profound exercise-induced oxygen desaturation (59%). For ST, most experts (68%) recommend 3 sets per exercise; 62% of experts set the intensity at a specific load that patients can tolerate for a range of 8 to 15 repetitions per set. Also, 56% of experts advise patients to approach local muscular exhaustion at the end of a single ST set. ConclusionsThe experts´ practices were summarized to develop practical recommendations in the form of flowcharts on how experts apply and adjust CET, IET, and ST in patients with CRDs. These recommendations may guide health care professionals to optimize exercise training programs in patients with CRDs.

Preventive effects of intense continuous endurance training on isoproterenol-induced cardiac apoptosis and protein synthesis gene expression in wistar rats

Objectives: Heart failure contributes to cellular lesions and left ventricular dysfunction. The present study aimed to determine the effects of intense continuous endurance training on protein synthesis gene expression and prevention of isoproterenol-induced cardiac apoptosis.&#x0D; Methods: In this experimental study, 16 male Wistar rats were assigned to exercise and control groups. After eight-week treadmill running, with 15° inclination, at 65-75% of VO2max for 30-60 minutes, Isoproterenol (3 mg/kg) was injected into the rats subcutaneously for 7 days. And 24 hours after the last injection, the left ventricular tissue was stored at -80°C for qRT-PCR and TUNEL assay. Between-group differences were determined by parametric and non-parametric tests, using SPSS software version 24.&#x0D; Results: There was a significant increase in mTORC1 gene expression in the training group (P = 0.026) but AMPK alterations failed to be significant. eEF2K gene expression was suppressed in the training group (P = 0.001) which resulted in a significant increase in eEF2 expression (P = 0.005). Left ventricular weight and heart weight/body weight increased compared to the control group (P = 0.028, P = 0.010, respectively). And the training protocol effectively prevented the formation of isoproterenol-induced apoptotic cells (P &lt;0.001).&#x0D; Conclusions: The exercise training protocol increased protein synthesis gene expression, and improved cardiac protection by reducing apoptosis. This protocol can be considered a promising modality in preventing and reducing apoptosis induced by heart disease such as myocardial infarction.

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.

Comparative Efficacy of 5 Exercise Types on Cardiometabolic Health in Overweight and Obese Adults: A Systematic Review and Network Meta-Analysis of 81 Randomized Controlled Trials.

Although regular exercise is recommended for preventing and treating overweight/obesity, the most effective exercise type for improving cardiometabolic health in individuals with overweight/obesity remains largely undecided. This network meta-analysis aimed to evaluate and rank the comparative efficacy of 5 exercise modalities on cardiometabolic health measures in individuals with overweight/obesity. A database search was conducted in MEDLINE, Embase, Scopus, and Web of Science from inception up to September 2020. The review focused on randomized controlled trials involving exercise interventions consisting of continuous endurance training, interval training, resistance training, combined aerobic and resistance training (combined training), and hybrid-type training. Exercise interventions aimed to improve somatometric variables, body composition, lipid metabolism, glucose control, blood pressure, cardiorespiratory fitness, and muscular strength. The Cochrane risk of bias tool was used to evaluate eligible studies. A random-effects network meta-analysis was performed within a frequentist framework. The intervention ranking was carried out using a Bayesian model where mean and SD were equal to the respective frequentist estimates. A total of 4331 participants (59% female; mean age: 38.7±12.3 years) from 81 studies were included. Combined training was the most effective modality and hybrid-type training the second most effective in improving cardiometabolic health-related outcomes in these populations suggesting a higher efficacy for multicomponent exercise interventions compared to single-component modalities, that is, continuous endurance training, interval training, and resistance training. A subgroup analysis revealed that the effects from different exercise types were mediated by gender. These findings corroborate the latest guidelines on exercise for individuals with overweight/obesity highlighting the importance of a multicomponent exercise approach to improve cardiometabolic health. Physicians and healthcare professionals should consider prescribing multicomponent exercise interventions to adults with overweight/obesity to maximize clinical outcomes. URL: https://www.crd.york.ac.uk/PROSPERO/; Unique identifier: CRD42020202647.

Effects of continuous cycling training on motor unit firing rates, input excitation, and myosin heavy chain of the vastus lateralis in sedentary females.

This study examined the effects of continuous endurance training on motor unit (MU) mean firing rates (MFR), percent myosin heavy chain (%MHC) isoforms, and muscle cross-sectional area (mCSA) of the vastus lateralis (VL). Twelve females completed 5-weeks of continuous cycling-training (CYC), while 8 females were controls (CON). Participants performed maximal voluntary contractions (MVCs) and 40% MVCs of the knee extensors before (PRE) and after the 5-week treatment period at the same absolute pre-treatment submaximal torque (POSTABS) and relative to post-treatment MVCs (POSTREL). Surface electromyographic (EMG) signals were decomposed with the Precision Decomposition III algorithm. MU firing times and waveforms were validated with reconstruct-and-test and spike trigger average procedures. MFRs at steady torque, recruitment thresholds (RT), and normalized EMG amplitude (N-EMGRMS) were analyzed. Y-intercepts and slopes were calculated for the MFR vs. RT relationships. MHC isoforms and mCSA were determined with muscle biopsies and ultrasonography. CYC decreased MVCs and type IIX %MHC isoform without changes in mCSA. The slopes for the MFR vs. RT relationships decreased for CYC during POSTREL and POSTABS while N-EMGRMS increased for POSTABS with no differences between PRE and POSTREL. Type I %MHC isoform was correlated with the slope for the MFR vs. RT relationship during POSTABS and POSTREL for CYC. This study provides evidence that decreases in the MFRs of higher threshold MUs post-CYC is likely a function of changes in input excitation (POSTABS) and the firing frequency-excitation relationships (POSTREL). Evidence is provided that MHC isoforms influence the firing rate scheme of the muscle following short-term training.

Association Between Changes in Serum and Skeletal Muscle Metabolomics Profile With Maximum Power Output Gains in Response to Different Aerobic Training Programs: The Times Study.

Purpose: High heterogeneity of the response of cardiorespiratory fitness (CRF) to standardized exercise doses has been reported in different training programs, but the associated mechanisms are not widely known. This study investigated whether changes in the metabolic profile and pathways in blood serum and the skeletal muscle are associated with the inter-individual variability of CRF responses to 8-wk of continuous endurance training (ET) or high-intensity interval training (HIIT).Methods: Eighty men, young and sedentary, were randomized into three groups, of which 70 completed 8 wk of intervention (> 90% of sessions): ET, HIIT, or control. Blood and vastus lateralis muscle tissue samples, as well as the measurement of CRF [maximal power output (MPO)] were obtained before and after the intervention. Blood serum and skeletal muscle samples were analyzed by 600 MHz 1H-NMR spectroscopy (metabolomics). Associations between the pretraining to post-training changes in the metabolic profile and MPO gains were explored via three analytical approaches: (1) correlation between pretraining to post-training changes in metabolites' concentration levels and MPO gains; (2) significant differences between low and high MPO responders; and (3) metabolite contribution to significantly altered pathways related to MPO gains. After, metabolites within these three levels of evidence were analyzed by multiple stepwise linear regression. The significance level was set at 1%.Results: The metabolomics profile panel yielded 43 serum and 70 muscle metabolites. From the metabolites within the three levels of evidence (15 serum and 4 muscle metabolites for ET; 5 serum and 1 muscle metabolites for HIIT), the variance in MPO gains was explained: 77.4% by the intervention effects, 6.9, 2.3, 3.2, and 2.2% by changes in skeletal muscle pyruvate and valine, serum glutamine and creatine phosphate, respectively, in ET; and 80.9% by the intervention effects; 7.2, 2.2, and 1.2% by changes in skeletal muscle glycolate, serum creatine and creatine phosphate, respectively, in HIIT. The most changed and impacted pathways by these metabolites were: arginine and proline metabolism, glycine, serine and threonine metabolism, and glyoxylate and dicarboxylate metabolism for both ET and HIIT programs; and additional alanine, aspartate and glutamate metabolism, arginine biosynthesis, glycolysis/gluconeogenesis, and pyruvate metabolism for ET.Conclusion: These results suggest that regulating the metabolism of amino acids and carbohydrates may be a potential mechanism for understanding the inter-individual variability of CRF in responses to ET and HIIT programs.

Examining interindividual differences in select muscle and whole-body adaptations to continuous endurance training.

What is the central question of the study? Do interindividual differences in trainability exist for morphological and molecular skeletal muscle responses to aerobic exercise training? What is the main finding and its importance? Interindividual differences in trainability were present for some, but not all, morphological and molecular outcomes included in our study. Our findings suggest that it is inappropriate, and perhaps erroneous, to assume that variability in observed responses reflects interindividual differences in trainability in skeletal muscle responses to aerobic exercise training. Studies have interpreted a wide range of morphological and molecular changes in human skeletal muscle as evidence of interindividual differences in trainability. However, these interpretations fail to account for the influence of random measurement error and within-subject variability. The purpose of the present study was to use the standard deviation of individual response (SDIR ) statistic to test the hypothesis that interindividual differences in trainability are present for some but not all skeletal muscle outcomes. Twenty-nine recreationally active males (age: 21±2years; BMI: 24±3kg/m2 ; ; 45±7ml/kg/min) completed 4weeks of continuous training (REL; n=14) or control (n=15). Maximal enzyme activities (citrate synthase and β-hydroxyacyl-CoA dehydrogenase), capillary density, fibre type composition, fibre-specific succinate dehydrogenase activity and substrate storage (intramuscular triglycerides and glycogen), and markers of mitophagy (BCL2-interacting protein 3 (BNIP3), BNIP3-like protein, parkin and PTEN-induced kinase 1) were measured in vastus lateralis samples collected before and after the intervention. We also calculated SDIR values for , peak work rate and the onset of blood lactate accumulation for the REL group and a separate group that exercised at the negative talk test stage. Although positive SDIR values - indicating interindividual differences in trainability - were obtained for aerobic capacity outcomes, maximal enzyme activities, capillary density, all fibre-specific outcomes and BNIP3 protein content, the remaining outcomes produced negative SDIR values indicating a large degree of random measurement error and/or within-subject variability. Our findings question the interpretation of heterogeneity in observed responses as evidence of interindividual differences in trainability and highlight the importance of including control groups when analysing individual skeletal muscle response to exercise training.

Effect of Exercise Training on Fat Loss-Energetic Perspectives and the Role of Improved Adipose Tissue Function and Body Fat Distribution.

In obesity, excessive abdominal fat, especially the accumulation of visceral adipose tissue (VAT), increases the risk of metabolic disorders, such as type 2 diabetes mellitus (T2DM), cardiovascular disease, and non-alcoholic fatty liver disease. Excessive abdominal fat is associated with adipose tissue dysfunction, leading to systemic low-grade inflammation, fat overflow, ectopic lipid deposition, and reduced insulin sensitivity. Physical activity is recommended for primary prevention and treatment of obesity, T2DM, and related disorders. Achieving a stable reduction in body weight with exercise training alone has not shown promising effects on a population level. Because fat has a high energy content, a large amount of exercise training is required to achieve weight loss. However, even when there is no weight loss, exercise training is an effective method of improving body composition (increased muscle mass and reduced fat) as well as increasing insulin sensitivity and cardiorespiratory fitness. Compared with traditional low-to-moderate-intensity continuous endurance training, high-intensity interval training (HIIT) and sprint interval training (SIT) are more time-efficient as exercise regimens and produce comparable results in reducing total fat mass, as well as improving cardiorespiratory fitness and insulin sensitivity. During high-intensity exercise, carbohydrates are the main source of energy, whereas, with low-intensity exercise, fat becomes the predominant energy source. These observations imply that HIIT and SIT can reduce fat mass during bouts of exercise despite being associated with lower levels of fat oxidation. In this review, we explore the effects of different types of exercise training on energy expenditure and substrate oxidation during physical activity, and discuss the potential effects of exercise training on adipose tissue function and body fat distribution.

Comparison of sprint interval and continuous endurance training on oxidative stress and antioxidant adaptations in young healthy adults

Background: Different intensities of exercise induce varying levels of reactive oxygen species, causing oxidative stress. However, regular physical training enhances the antioxidant system and protects tissues by oxidative stress. This study aimed to investigate the difference in markers between time-efficient low-volume high intensity interval (sprint interval training: SIT) and traditional high-volume low-intensity methods (continuous endurance training: CET) regarding oxidative stress and antioxidant levels. Material and methods: Fifteen male volunteers were divided into two groups according to their VO2max levels. The SIT program consisted of 4–6 Wingate all-out sprints with a 4.5 min recovery, while CET consisted of 30–50 min cycling at 60% VO2max for seven weeks. Total oxidant status (TOS), total antioxidant status (TAS), plasma malondialdehyde (MDA) and glutathione peroxidase (GSH-Px) levels were examined in pre and post-intervention. Results: Increases in GSH-Px (30% vs. 55%), TOS (33% vs. 18%) and a significant decrease in MDA (8.6%, p&lt;0.003; 6.8%, p&lt;0.016) in CET and SIT were observed, respectively. By contrast, TAS decreased (62%) after CET and increased (17%) after SIT. No significant differences in these parameters were reported after the training period between SIT and CET groups. Conclusions: SIT was suggested as a safe exercise model to improve general health and the performance of traditional CET.

The Effect of High- and Moderate-intensity Endurance Training on Some Anabolic/Catabolic Osteokines in Old Male Wistar Rats

Background: Bone-related osteokines are crucial for bone function and metabolic response to physical activity. The present study aimed to shed light on the effect of different intensities of continuous and interval endurance training on the serum levels of some osteokines that are associated with wingless-related integration site (WNT) signaling pathway and Receptor Activator of Nuclear Factor (NF)-κB Ligand (RANKL) in old male Wistar rats. Materials and Methods: A total of 24 old male Wistar rats (mean age: 23 months, mean weight: 437.93 g) were randomly assigned to three groups: interval endurance-training group (n=8), continuous endurance-training group (n=8), and control group (n=8). The continuous and interval training interventions comprised 8 weeks of treadmill exercise, 5 days a week. The continuous endurance-training group started to exercise at 60% of velocity at maximal oxygen uptake (vVO2max) for 16 min during the first week. It continued with 70% of vVO2max for 45 min from the fourth week onward. In contrast, the interval endurance-training group switched on exercise with 40%-80% of vVO2max from the first week and persisted with 30%-110% of vVO2max from the fourth week onward. As the exercise bout was completed, the enzyme-linked immunosorbent assay was applied to measure the study dependent variables. Statistical analysis was further performed using 1-way analysis of variance, considering the significance level of P≤0.05. Results: The study results demonstrated a significant difference in the levels of Oteoprotegerin (OPG) (P=0.036) and RANKL (P=0.001) in the experimental (namely, interval and continuous training) groups compared with the controls following the exercise bout. However, the level of sclerostin was not significantly changed (P=0.549). Conclusion: High-intensity endurance training in the RANKL/OPG and WNT pathways decreased sclerostin and RANKL levels, but this decrease was significant at the RANKL level. It was effective with regard to the intensities of different types of endurance exercise.

Protective effects of HIIT vs. CET exercise training on high-fat-high-fructose diet-induced hyperglycemia, hyperlipidemia, and histopathology of liver in rats: regulation of SIRT1/PGC-1α

Disruption of the function of sirtuin1 (SIRT1) has been reported to link with diabetes and metabolic disorders. The aim of this study was to investigate the effect of a modified high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) or continuous endurance training (CET) program on Sirt1 and PGC-1α mRNA gene expression in hepatocytes of high-fat/high-fructose diet-induced diabetes in rats. Twenty-eight male Wistar rats (220 ± 20 g) were randomly divided into four groups of non-diabetic (NDC), diabetic control (received high fat high-fructose diet (HFHFD-DC)), CET (HFHFD-CET), and HIIT (HFHFD-HIIT). Diabetes was induced by feeding rats a high-fat (30%) high-fructose (20%) diet for 25 weeks. Following confirmed hyperglycemia, both HFHFD-CET (60–65% Vo2max) and HFHFD-HIIT (85–90% Vo2max) rats underwent treadmill exercise for 30 min, 5 days/week at 10 m/min for 8 weeks. Thereafter, blood and liver samples were obtained for biochemical studies. For histological analysis, the liver was fixed in 10% formalin, embedded in paraffin, and sectioned (5 μm thickness) for H&E staining. SIRT-1 and PGC-1α mRNA expression were measured by RT-PCR from the liver sample (frizzed sample). All data were presented as mean ± standard error mean and compared the differences by one-way analysis of variances. The alpha level was set at 0.05 (p < 0.05) for statistical difference. The results show that HIIT was more effective than CET to reduce vesicular steatosis. HIIT significantly enhanced the expression of SIRT-1 compared to the HFHFD-DC group (fold change: 1.47, p < 0.047). However, HIIT decreased PGC-1α expression compared to the HFHFD-DC group, but it was not significant (fold change: 1.32 and p < 0.247). HIIT was more effective than CET in SIRT-1 expression augmentation in high-fat, high-fructose diabetic rats which suggests a possible treatment strategy in the context of type 2 diabetes.