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This study aimed to verify the effects of 4 weeks of high-intensity interval training (HIIT), heavy (HRT) and explosive (ERT) resistance training on aerobic, anaerobic and neuromuscular parameters and performance of well-trained runners. Twenty-six male athletes were divided into HIIT (n = 10), HRT (n = 7) and ERT (n = 9) groups. Maximal oxygen uptake (VO2max) and the corresponding velocity (vVO2max), anaerobic threshold (AT), running economy (RE), oxygen uptake kinetics, lower-body strength (1RM) and power (CMJ), and the 1500m and 5000m time-trial (TT) were determined. Improvements were observed in vVO2max (mean difference (Δ): 2.6%; effect size (ES): 0.63) with HIIT, while AT was incresead in ERT (Δ: 4.3%; ES: 0.73) and HRT (Δ: 6.9%; ES: 0.72) groups. The CMJ performance was increased in ERT (Δ: 13.8%; ES: 1.03), HRT (Δ: 6.9%; ES: 0.55) and HIIT (Δ: 5.4%; ES: 0.34), whereas 1RM increase in HRT (Δ: 38.1%; ES: 1.21) and ERT (Δ: 49.2%; ES: 0.96) groups. HIIT improved the 1500m (Δ: -2.3%; ES: -0.62) and both HRT (Δ: -1.6%; ES: -0.32) and ERT (Δ: -1.7%; ES: -0.31) the 5000m TT. Despite performance adaptations were dependent on the training characteristics, both RT and HIIT model constitute an alternative for training periodization.

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The present study investigated the reliability and sensitivity of a wearable near-infrared spectroscopy (wNIRS) device in moderate and heavy exercise intensity domains. On three separate days, eleven males performed an incremental test to exhaustion, and in the following visits, four submaximal constant-load bouts (i.e., test and retest) were performed in the moderate-intensity domain (100 and 130 W) and heavy-intensity domain (160 and 190 W). The local tissue oxygen saturation index (SmO2) and pulmonary oxygen uptake (V̇O2) were measured continuously. The absolute SmO2 and V̇O2 values and the change (Δ) from the 3rd to 6th min of exercise were calculated. There was good reliability for SmO2 measurements, as indicated by the high intraclass correlation coefficient analysis (ICC ≥0.84 for all) and low coefficient of variation between the two trials (CV ≤4.1% for all). Steady-state responses were observed for SmO2 and V̇O2 from the 3rd to the 6th min in the two moderate-intensity bouts (P>0.05), whereas SmO2 decreased and V̇O2 increased from the 3rd to the 6th min in the two heavy-intensity bouts (P<0.05). Together, these findings suggested that the SmO2 measured with a wNIRS device is reliable and sensitive to track local metabolic changes provoked by slight increments in exercise intensity.

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This study investigated the effectiveness of supplementing regular preseason soccer training with a supramaximal intermittent shuttle-run training (ISRT) model prescribed from Carminatti's Test peak speed (PST-CAR) in aerobic performance-related indices and sprinting speed in male junior soccer players. Twenty-three national-level soccer players (mean ± SD; age 18.07 ± 0.9 y, body height 1.76 ± 0.65 m, body mass 71.9 ± 8.7 kg) were assigned to either an experimental group (EG; n = 13) performing ISRT + soccer training or a control group (CG; n = 10) that followed regular preseason soccer training alone. The following tests were applied before and after the eight-week training intervention: (i) incremental treadmill tests (VO2max and lactate minimum speed - LMS); (ii) linear 30-m sprint test and Carminatti's Test (PST-CAR). Results indicated larger gains for the EG in LMS (Δ = 9.53% vs. 2.82%) and PST-CAR (Δ = 5.50% vs. 2.10%) than in the CG. Furthermore, changes in VO2max produced higher effect size (d) values for the EG (Δ = 6.67%; d = 0.59) than the CG (Δ = 1.88%; d = 0.18). Both groups improved (p = 0.002) their flying 20-m sprint speed (EG: Δ = 1.01%; CG: Δ = 1.56%). However, small decreases were observed for 10-m sprint speed in the CG (Δ = -2.19%; d = -0.44), while only trivial changes were noticed for the EG (Δ = -0.50%; d = -0.16). Our data support that additional supramaximal ISRT is an effective training stimulus to enhance aerobic performance-related indices and promote small improvements in maximal running speed without impairing the soccer players' acceleration capacity. This study also shows that PST-CAR can be useful for individualizing running intensity in supramaximal ISRT modes.

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This study aimed to assess the predictive capability of different critical power (CP) models on cycling exercise tolerance in the severe- and extreme-intensity domains. Nineteen cyclists (age: 23.0 ± 2.7 y) performed several time-to-exhaustion tests (Tlim) to determine CP, finite work above CP (W'), and the highest constant work rate at which maximal oxygen consumption was attained (IHIGH). Hyperbolic power-time, linear power-inverse of time, and work-time models with three predictive trials were used to determine CP and W'. Modeling with two predictive trials of the CP work-time model was also used to determine CP and W'. Actual exercise tolerance of IHIGH and intensity 5% above IHIGH (IHIGH+5%) were compared to those predicted by all CP models. Actual IHIGH (155 ± 30 s) and IHIGH+5% (120 ± 26 s) performances were not different from those predicted by all models with three predictive trials. Modeling with two predictive trials overestimated Tlim at IHIGH+5% (129 ± 33 s; p = 0.04). Bland-Altman plots of IHIGH+5% presented significant heteroscedasticity by all CP predictions, but not for IHIGH. Exercise tolerance in the severe and extreme domains can be predicted by CP derived from three predictive trials. However, this ability is impaired within the extreme domain.

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Background: The 6-minute rowing ergometer test (6-minRT) is valid and reliable for establishing maximal aerobic power (MAP) in amateur male rowers. However, ventilatory thresholds (VTs) have not yet been established with their mechanical correspondence in this test. Objective: The primary objective was to determine the VTs in the 6-minRT achieved by amateur male rowers, while the secondary objective was to determine the correspondence between ventilatory, mechanical, and heart rate (HR) outcomes of the 6-minRT. Methods: Sixteen amateur male rowers were part of the study. All participants were instructed to perform an incremental test (IT) and a 6-minRT. Determination of the ventilatory parameters for the first ventilatory threshold (VT1), the second ventilatory threshold (VT2), and 6minRTVO2max were performed by correlating the outcomes of VT1, VT2, and VO2max obtained in the IT, with the outcomes of 6-minRT. For these purposes, Pearson's test was used, with the following criteria: trivial, <0.1; small, 0.1-0.3; moderate, 0.3-0.5; high, 0.5-0.7; very high, 0.7-0.9; or practically perfect, >0.9. The significance level was p < 0.05. Results: The IT analysis determined that VT1 and VT2 correspond to 55 and 80% of VO2max, respectively. A high correlation was observed between IT outcomes in VT1, VT2, and VO2max, with the outcomes of 6-minRT (r > 0.6). Conclusion: Based on IT ventilatory parameters and concordance analysis, VT1 and VT2 of 6-minRT are determined at 55 and 80%, respectively, of both ventilatory parameters and their corresponding mechanical outcomes and HR.

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PURPOSE: To perform a cross-cultural adaptation of the OMNI verbal descriptors to Brazilian-Portuguese and examine the validity of the Brazilian version for arm-crank activity. MATERIALS AND METHODS: Cross-cultural adaptation stages were: permission, translation, synthesis, back translation, expert committee review, pretesting, and submission and appraisal. For the concurrent validity, a Brazilian OMNI-Wheel scale was used to obtain rating of perceived exertion for the overall body (RPEOverall) and arms (RPEArms) in participants (n = 9, 10-17 years) with spina bifida. Cardiopulmonary exercise test was used to measure heart rate (HR) and oxygen uptake (VO2). Repeated Measures Correlation (rrm) was used to examine the scale validity. RESULTS: The cross-cultural adaptation produced equivalence between English and Brazilian-Portuguese verbal descriptors based on successful translation and pretesting. The Brazilian OMNI-wheel was validated based on strong associations of RPEOverall with VO2 (rrm (35) = 0.86, 95% CI [0.93, 0.73], p < 0.001) and HR (rrm (35) = 0.89, 95% CI [0.94, 0.79], p < 0.001) and RPEArms with VO2 (rrm (33) = 0.82, 95% CI [0.91, 0.66], p < 0.001) and HR (rrm (33) = 0.82, 95% CI [0.91, 0.66], p < 0.001). CONCLUSIONS: The OMNI scale was cross-culturally adapted to Brazilian-Portuguese. The Brazilian OMNI-Wheel was validated based on strong associations of RPE with HR and VO2. Implications For RehabilitationThe original English OMNI was cross-culturally adapted to Brazilian-Portuguese.A Brazilian wheelchair OMNI was concurrently validated for Arm-Crank Activity in adolescents with spina bifida.This OMNI scale version may aid health providers in monitoring perceived exertion in Brazil.

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Purpose: This study aimed to evaluate the physiological responses associated with the stroke length (SL) and stroke rate (SR) changes as swimming velocity increases during an incremental step-test. Moreover, this study also aimed to verify if SL and SR relationships toward maximal oxygen uptake (V̇O2max), gas respiratory compensation point (RCP), exchange threshold (GET), and swimming cost can be applied to the management of endurance training and control aerobic pace. Methods: A total of 19 swimmers performed the incremental test until volitional exhaustion, with each stage being designed by percentages of the 400 m (%v400) maximal front crawl velocity. V̇O2max, GET, RCP, and the respective swimming velocities (v) were examined. Also, the stroke parameters, SL, SR, the corresponding slopes (SLslope and SRslope), and the crossing point (Cp) between them were determined. Results: GET and RCP corresponded to 70.6% and 82.4% of V̇O2max (4185.3 ± 686.1 mL min-1), and V̇O2 at Cp, SLslope, and SRslope were observed at 129.7%, 75.3%, and 61.7% of V̇O2max, respectively. The swimming cost from the expected V̇O2 at vSLslope (0.85 ± 0.18 kJ m-1), vSRslope (0.77 ± 0.17 kJ m-1), and vCp (1.09 ± 0.19 kJ m-1) showed correlations with GET (r = 0.73, 0.57, and 0.59, respectively), but only the cost at vSLslope and vCp correlated to RCP (0.62 and 0.69) and V̇O2max (0.70 and 0.79). Conclusion: SL and SR exhibited a distinctive pattern for the V̇O2 response as swimming velocity increased. Furthermore, the influence of SL on GET, RCP, and V̇O2max suggests that SLslope serves as the metabolic reference of heavy exercise intensity, beyond which the stroke profile defines an exercise zone with high cost, which is recommended for an anaerobic threshold and aerobic power training. In turn, the observed difference between V̇O2 at SRslope and GET suggests that the range of velocities between SL and SR slopes ensures an economical pace, which might be recommended to develop long-term endurance. The results also highlighted that the swimming intensity paced at Cp would impose a high anaerobic demand, as it is located above the maximal aerobic velocity. Therefore, SLslope and SRslope are suitable indexes of submaximal to maximal aerobic paces, while Cp's meaning still requires further evidence.

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This study aimed to apply an incremental tethered swimming test (ITT) with workloads (WL) based on individual rates of front crawl mean tethered force (Fmean) for the identification of the upper boundary of heavy exercise (by means of respiratory compensation point, RCP), and therefore to describe oxygen uptake kinetics (VO2k) and time limit (tLim) responses to WL corresponding to peak oxygen uptake (WLVO2peak). Sixteen swimmers of both sexes (17.6 ± 3.8 years old, 175.8 ± 9.2 cm, and 68.5 ± 10.6 kg) performed the ITT until exhaustion, attached to a weight-bearing pulley-rope system for the measurements of gas exchange threshold (GET), RCP, and VO2peak. The WL was increased by 5% from 30 to 70% of Fmean at every minute, with Fmean being measured by a load cell attached to the swimmers during an all-out 30 s front crawl bout. The pulmonary gas exchange was sampled breath by breath, and the mathematical description of VO2k used a first-order exponential with time delay (TD) on the average of two rest-to-work transitions at WLVO2peak. The mean VO2peak approached 50.2 ± 6.2 mL·kg-1·min-1 and GET and RCP attained (respectively) 67.4 ± 7.3% and 87.4 ± 3.4% VO2peak. The average tLim was 329.5 ± 63.6 s for both sexes, and all swimmers attained VO2peak (100.4 ± 3.8%) when considering the primary response of VO2 (A1' = 91.8 ± 6.7%VO2peak) associated with the VO2 slow component (SC) of 10.7 ± 6.7% of end-exercise VO2, with time constants of 24.4 ± 9.8 s for A1' and 149.3 ± 29.1 s for SC. Negative correlations were observed for tLim to VO2peak, WLVO2peak, GET, RCP, and EEVO2 (r = -0.55, -0.59, -0.58, -0.53, and -0.50). Thus, the VO2k during tethered swimming at WLVO2peak reproduced the physiological responses corresponding to a severe domain. The findings also demonstrated that tLim was inversely related to aerobic conditioning indexes and to the ability to adjust oxidative metabolism to match target VO2 demand during exercise.

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BACKGROUND: Weber classification stratifies cardiac patients based on peak oxygen consumption (V̇O2), the gold-standard measure of exercise capacity. OBJECTIVE: To determine if Weber classification is a useful tool to discriminate clinical phenotypes in COPD patients and to evaluate if disease severity and other clinical measures can predict V̇O2peak. METHODS: Three hundred and six COPD patients underwent cardiopulmonary exercise testing (CPX) and were divided according to Weber class: 1) Weber A (n = 34); 2) Weber B (n = 88); 3) Weber C (n = 138); and 4) Weber D (n = 46). RESULTS: Weber class D patients demonstrated a reduced V̇O2 peak, heart rate (HR), minute ventilation (V̇E), oxygen (O2) pulse, circulatory power (CP), oxygen uptake efficiency slope (OUES), oxygen saturation (SpO2%), delta (Δ)HR and ΔSpO2 when compared to Weber A and B (p<0.05). Moreover, Dyspnea and the V̇E/carbon dioxide production (V̇CO2) slope were higher in Weber D compared with Weber C and A (p<0.001). Hierarchical regression analysis demonstrated significant predictors of V̇O2peak (R2= 0.131; Adj R 2 = 1.25), including HR (ß=0.5757; t = 5.7; P<0.001) and forced expiratory volume in one second (FEV1) (ß=0.119; t = 2.16; P<0.03). Among the Weber C + D groups, predictors of V̇O2peak (R = 0.78; R2= 0.60; Adj R2 =0.59), dyspnea (ß=0.076; t = 1.111; P<0.27) and maximal voluntary ventilation (MVV) (ß=0.75; t = 1.14; P<0.00). CONCLUSION: Weber classification may be a useful tool to stratify cardiorespiratory fitness in COPD patients. Other clinical measures may be useful in predicting peak V̇O2 in mild-to-severe COPD, moreover different phenotypes may be important tool to improve physical capacity of chronic disease patients.

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BACKGROUND: Cardiopulmonary Exercise Testing (CPX) is essential for the assessment of exercise capacity for patients with Chronic Heart Failure (CHF). Respiratory gas and hemodynamic parameters such as Ventilatory Efficiency (VE/VCO2 slope), peak oxygen uptake (peak VO2), and heart rate recovery are established diagnostic and prognostic markers for clinical populations. Previous studies have suggested the clinical value of metrics related to respiratory gas collected during recovery from peak exercise, particularly recovery time to 50% (T1/2) of peak VO2. The current study explores these metrics in detail during recovery from peak exercise in CHF. METHODS: Patients with CHF who were referred for CPX and healthy individuals without formal diagnoses were assessed for inclusion. All subjects performed CPX on cycle ergometers to volitional exhaustion and were monitored for at least five minutes of recovery. CPX data were analyzed for overshoot of respiratory exchange ratio (RER=VCO2/VO2), ventilatory equivalent for oxygen (VE/VO2), end-tidal partial pressure of oxygen (PETO2), and T1/2 of peak VO2 and VCO2. RESULTS: Thirty-two patients with CHF and 30 controls were included. Peak VO2 differed significantly between patients and controls (13.5 ± 3.8 vs. 32.5 ± 9.8 mL/Kg*min-1, p < 0.001). Mean Left Ventricular Ejection Fraction (LVEF) was 35.9 ± 9.8% for patients with CHF compared to 61.1 ± 8.2% in the control group. The T1/2 of VO2, VCO2 and VE was significantly higher in patients (111.3 ± 51.0, 132.0 ± 38.8 and 155.6 ± 45.5s) than in controls (58.08 ± 13.2, 74.3 ± 21.1, 96.7 ± 36.8s; p < 0.001) while the overshoot of PETO2, VE/VO2 and RER was significantly lower in patients (7.2 ± 3.3, 41.9 ± 29.1 and 25.0 ± 13.6%) than in controls (10.1 ± 4.6, 62.1 ± 17.7 and 38.7 ± 15.1%; all p < 0.01). Most of the recovery metrics were significantly correlated with peak VO2 in CHF patients, but not with LVEF. CONCLUSIONS: Patients with CHF have a significantly blunted recovery from peak exercise. This is reflected in delays of VO2, VCO2, VE, PETO2, RER and VE/VO2, reflecting a greater energy required to return to baseline. Abnormal respiratory gas kinetics in CHF was negatively correlated with peak VO2 but not baseline LVEF.

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INTRODUCTION: Since sex-specific accumulated oxygen deficit (AOD) during high-intensity swimming remains unstudied, this study aimed to assess AOD during 50, 100, and 200 m front-crawl performances to compare the responses between sexes and analyse the effect of lean body mass (LBM). METHODS: Twenty swimmers (16.2 ± 2.8 years, 61.6 ± 7.8 kg, and 48.8 ± 11.2 kg LBM-50% males) performed 50, 100, and 200 m to determine accumulated oxygen uptake (V̇O2Ac). The swimmers also performed an incremental test from which five submaximal steps were selected to estimate the oxygen demand (V̇O2demand) from the V̇O2 versus velocity adjustment. V̇O2 was sampled using a gas analyser coupled with a respiratory snorkel. AOD was the difference between V̇O2demand and V̇O2Ac, and LBM (i.e. lean mass not including bone mineral content) was assessed by dual-energy X-ray absorptiometry (DXA). RESULTS: A two-way ANOVA evidenced an AOD increase with distance for both sexes: 19.7 ± 2.5 versus 24.9 ± 5.5, 29.8 ± 8.0 versus 36.5 ± 5.8, and 41.5 ± 9.4 versus 5.2 ± 11.9 ml × kg-1, respectively, for 50, 100, and 200 m (with highest values for females, P < 0.01). Inverse correlations were observed between LBM and AOD for 50, 100, and 200 m (r = - 0.60, - 0.38 and - 0.49, P < 0.05). AOD values at 10 and 30 s elapsed times in each trial decreased with distance for both sexes, with values differing when female swimmers were compared to males in the 200 m trial (at 10 s: 2.6 ± 0.6 vs. 3.4 ± 0.6; and at 30 s: 7.9 ± 1.7 vs. 10.0 ± 1.8 ml × kg-1, P < 0.05). CONCLUSION: LBM differences between sexes influenced AOD values during each trial, suggesting that reduced muscle mass in female swimmers plays a role on the higher AOD (i.e. anaerobic energy) demand than males while performing supramaximal trials.

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Prolonged rowing exercise sessions are often prescribed considering competitive training schedules, and under hostile environments (e.g., heated ambient). The study aimed to investigate the effect of heat stress (HS) on physical performance, Lactate concentration ([Lac]), and cardiorespiratory responses during prolonged exercise sessions in competitive rowers. Twelve rowers performed preliminary exercise tests (2-km test and five-step incremental lactate test) to assess the target workload intensity corresponding to a 2.5 mmol.L-1 of [Lac]. On two separate days, participants were enrolled in two exercise sessions of 12 km in a rowing machine under HS (∼30 °C) and thermal comfort (TC 22 °C) conditions. Heart rate (HR), stroke volume (SV), cardiac output (CO), oxygen uptake (VO2), [Lac], and the rating of perceptual exertion (RPE) were obtained. From baseline, HS increased the maximum temperature of the face compared to TC. Workload and VO2 reduced while RPE increased at 9- and 12-km of rowing exercise under HS compared to TC. From baseline to the last stage of exercise, HS shifted SV downwards and HR upwards compared to TC. Consequently, CO did not change between thermal conditions (TC vs. HS). Therefore, HS provokes a cardiovascular drift during prolonged rowing in comparison to TC. The last stages of prolonged rowing sessions under HS seem to be critical to physical performance and relative perceptual of effort in rowers.

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BACKGROUND: Post-menopausal women have impaired cardiorespiratory responses to exercise compared to young women. Exercise training may counterbalance impairments, but the time-dependent effects of exercise training remain unclear. The current study aims to investigate the effects of rowing training on maximal aerobic capacity and time-course cardiorespiratory adaptations in older women. METHODS: Female participants (n = 23) were randomly allocated to the experimental group (EXP; n = 23; 66 ± 5 years old) enrolled in rowing exercise training and control group (CON; n = 10; 64 ± 4 years old). The cardiopulmonary exercise test (CET) was performed in a cycle ergometer pre- and post-interventions. Oxygen uptake (VO2), stroke volume (SV), cardiac output (CO), and HR were recorded during CET and analyzed at the peak of the exercise. HR was monitored during exercise recovery, and the index of HRR was calculated by ΔHRR (HRpeak-HR one-minute recovery). Every two weeks, Rowing Stepwise Exercise (RSE) in a rowing machine was performed to track specific adaptations to the exercise modality. HR was continuously recorded during RSE and corrected for the average power of each step (HR/watts). The rowing training protocol consisted of three weekly sessions of 30 min at an intensity corresponding to 60-80% of peak HR for ten weeks. RESULTS: Rowing exercise training increased VO2, SV, and CO at the peak of the CET, and ΔHRR. Increased workload (W) and reduced HR response to a greater achieved workload (HR/W) during RSE were observed after six weeks of training. CONCLUSIONS: Rowing exercise training is a feasible method to improve cardiorespiratory performance, vagal reactivation and heart rate adjustments to exercise in older women.

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Antimony (Sb) is a toxic and carcinogenic metalloid that can be present in contaminated water generated by mining operations and other industrial activities. The toxicity of Sb (III) and Sb (V) to aerobic microorganisms remains limited and unexplored for anaerobic microorganisms involved in hydrogen (H2) and methane (CH4) production. This study aimed to evaluate the toxicity of Sb (III) and Sb (V) upon aerobic and anaerobic microorganisms important in biological wastewater treatment systems. Sb (III) was more toxic than Sb (V) independently of the test and environment evaluated. Under aerobic conditions maintained in the Microtox assay, Sb (V) was not toxic to Allivibrio fischeri at concentrations as high as 500 mg/L, whereas Sb (III) caused just over 50% inhibition at concentration of 250 mg/L after 5 min of exposure. In the respirometry test, for the specific oxygen uptake rate, the concentrations of Sb (III) and Sb (V) displaying 50% inhibition were 0.09 and 56.2 mg/L, respectively. Under anaerobic conditions, exposure to Sb (III) and Sb (V) led to a decrease in microorganisms activity of fermentative and methanogenic processes. The results confirm that the microbial toxicity of Sb depends on its speciation and Sb (III) displays a significantly higher inhibitory potential than Sb (V) in both aerobic and anaerobic environments.

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NEW FINDINGS: What is the central question of this study? What are the physiological mechanisms underlying muscle fatigue and the increase in the O2 cost per unit of work during high-intensity exercise? What is the main finding and its importance? Muscle fatigue happens before, and does not explain, the V ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ slow component ( V ̇ O 2 sc ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}{\rm{sc}}}$ ), but they share the same origin. Muscle activation heterogeneity is associated with muscle fatigue and V ̇ O 2 sc ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}{\rm{sc}}}$ . Knowing this may improve training prescriptions for healthy people leading to improved public health outcomes. ABSTRACT: This study aimed to explain the V ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ slow component ( V ̇ O 2 sc ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}{\rm{sc}}}$ ) and muscle fatigue during cycling at different intensities. The muscle fatigue of 16 participants was determined through maximal isokinetic effort lasting 3 s during constant work rate bouts of moderate (MOD), heavy (HVY) and very heavy intensity (VHI) exercise. Breath-by-breath V ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ , near-infrared spectroscopy signals and EMG activity were analysed (thigh muscles). V ̇ O 2 sc ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}{\rm{sc}}}$ was higher during VHI exercise (∼70% vs. ∼28% of V ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ reserve in HVY). The deoxygenated haemoglobin final value during VHI exercise was higher than during HVY and MOD exercise (∼90% of HHb physiological normalization, vs. ∼82% HVY and ∼45% MOD). The muscle fatigue was greater after VHI exercise (∼22% vs. HVY ∼5%). There was no muscle fatigue after MOD exercise. The greatest magnitude of muscle fatigue occurred within 2 min (VHI ∼17%; HVY ∼9%), after which it stabilized. No significant relationship between V ̇ O 2 sc ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}{\rm{sc}}}$ and muscle force production was observed. The τ of muscle V ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ was significantly related (R2  = 0.47) with torque decrease for VHI. Type I and II muscle fibre recruitment mainly in the rectus femoris moderately explained the muscle fatigue (R2  = 0.30 and 0.31, respectively) and the V ̇ O 2 sc ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}{\rm{sc}}}$ (R2  = 0.39 and 0.27, respectively). The V ̇ O 2 sc ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}{\rm{sc}}}$ is also partially explained by blood lactate accumulation (R2  = 0.42). In conclusion muscle fatigue and O2 cost seem to share the same physiological cause linked with a decrease in the muscle V ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ and a change in lactate accumulation. Muscle fatigue and V ̇ O 2 sc ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}{\rm{sc}}}$ are associated with muscle activation heterogeneity and metabolism of different muscles activated during cycling.

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ABSTRACT Measuring cardiorespiratory variables can be challenging in developing animals, especially when they use bimodal gas exchange to maintain metabolic activity. In tadpoles, gas exchange may occur through the integument and gills when breathing in the water and through the lungs when breathing air, with varying contributions of each respiratory structure during development. The interaction between aquatic and air breathing results in a complex physiological response that may affect the cardiac cycle. Measuring the heart rate (fH) together with aquatic and aerial gas exchange in anurans during their development can be challenging, since it may involve handling small animals and/or a certain degree of invasiveness (i.e., surgery to implant electrodes). Here, we evaluated concomitantly aquatic and aerial gas exchange, lung ventilation, and fH in three stages of development of the bullfrog Lithobates catesbeianus (Shaw, 1802). We built a novel, noninvasive, closed respirometry system capable of measuring fH, aerial and aquatic gas exchange simultaneously in animals of different sizes. Our integrative analysis revealed a decrease in the heart rate and an increase in oxygen consumption during the developmental stages of the bullfrog, but there was no adjustment of heart rate after or during air breathing. Moreover, tadpoles in metamorphosis showed higher oxygen consumption in air than in water, while aquatic breathing was responsible for releasing CO2. Our results are consistent with those found in the literature, yet our study represents the first non-invasive investigation to evaluate bimodal gas exchange and heart rate simultaneously. Moreover, our setup holds potential for further advancements that would allow for controlled water and air composition. This tool could greatly facilitate the investigation of how cardiorespiratory physiology responds to varying environmental conditions.

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Abstract Background Cardiopulmonary Exercise Testing (CPX) is essential for the assessment of exercise capacity for patients with Chronic Heart Failure (CHF). Respiratory gas and hemodynamic parameters such as Ventilatory Efficiency (VE/VCO2 slope), peak oxygen uptake (peak VO2), and heart rate recovery are established diagnostic and prognostic markers for clinical populations. Previous studies have suggested the clinical value of metrics related to respiratory gas collected during recovery from peak exercise, particularly recovery time to 50% (T1/2) of peak VO2. The current study explores these metrics in detail during recovery from peak exercise in CHF. Methods Patients with CHF who were referred for CPX and healthy individuals without formal diagnoses were assessed for inclusion. All subjects performed CPX on cycle ergometers to volitional exhaustion and were monitored for at least five minutes of recovery. CPX data were analyzed for overshoot of respiratory exchange ratio (RER=VCO2/VO2), ventilatory equivalent for oxygen (VE/VO2), end-tidal partial pressure of oxygen (PETO2), and T1/2 of peak VO2 and VCO2. Results Thirty-two patients with CHF and 30 controls were included. Peak VO2 differed significantly between patients and controls (13.5 ± 3.8 vs. 32.5 ± 9.8 mL/Kg*min−1, p < 0.001). Mean Left Ventricular Ejection Fraction (LVEF) was 35.9 ± 9.8% for patients with CHF compared to 61.1 ± 8.2% in the control group. The T1/2 of VO2, VCO2 and VE was significantly higher in patients (111.3 ± 51.0, 132.0 ± 38.8 and 155.6 ± 45.5s) than in controls (58.08 ± 13.2, 74.3 ± 21.1, 96.7 ± 36.8s; p < 0.001) while the overshoot of PETO2, VE/VO2 and RER was significantly lower in patients (7.2 ± 3.3, 41.9 ± 29.1 and 25.0 ± 13.6%) than in controls (10.1 ± 4.6, 62.1 ± 17.7 and 38.7 ± 15.1%; all p < 0.01). Most of the recovery metrics were significantly correlated with peak VO2 in CHF patients, but not with LVEF. Conclusions Patients with CHF have a significantly blunted recovery from peak exercise. This is reflected in delays of VO2, VCO2, VE, PETO2, RER and VE/VO2, reflecting a greater energy required to return to baseline. Abnormal respiratory gas kinetics in CHF was negatively correlated with peak VO2 but not baseline LVEF.

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The amount of anerobic energy released during exercise might modify the initial phase of oxygen recovery (fast-O2debt) post-exercise. Therefore, the present study aimed to analyze the reliability of peak oxygen uptake ( V ˙ O 2 p e a k ) estimate by back-extrapolation ( B E - V ˙ O 2 p e a k ) under different swimming conditions in the severe-intensity domain, verifying how the alterations of the V ˙ O 2 recovery profile and anerobic energy demand might affect B E - V ˙ O 2 p e a k values. Twenty swimmers (16.7 ± 2.4 years, 173.5 ± 10.2 cm, and 66.4 ± 10.6 kg) performed an incremental intermittent step protocol (IIST: 6 × 250 plus 1 × 200 m, IIST_v200m) for the assessment of V ˙ O 2 p e a k . The V ˙ O 2 off-kinetics used a bi-exponential model to discriminate primary amplitude, time delay, and time constant (A1off, TD1off, and τoff) for assessment of fast-O2debt post IIST_v200m, 200-m single-trial (v200 m), and rest-to-work transition at 90% delta (v90%Δ) tests. The linear regression estimated B E - V ˙ O 2 p e a k and the rate of V ˙ O 2 recovery (BE-slope) post each swimming performance. The ANOVA (Sidak as post hoc) compared V ˙ O 2 p e a k to the estimates of B E - V ˙ O 2 p e a k in v200 m, IIST_v200 m, and v90%Δ, and the coefficient of dispersion (R2) analyzed the association between tests. The values of V ˙ O 2 p e a k during IIST did not differ from B E - V ˙ O 2 p e a k in v200 m, IIST_v200 m, and v90%Δ (55.7 ± 7.1 vs. 53.7 ± 8.2 vs. 56.3 ± 8.2 vs. 54.1 ± 9.1 ml kg-1 min-1, p > 0.05, respectively). However, the V ˙ O 2 p e a k variance is moderately explained by B E - V ˙ O 2 p e a k only in IIST_v200 m and v90%Δ (RAdj 2 = 0.44 and RAdj 2 = 0.43, p < 0.01). The TD1off and τoff responses post IIST_v200 m were considerably lower than those in both v200 m (6.1 ± 3.8 and 33.0 ± 9.5 s vs. 10.9 ± 3.5 and 47.7 ± 7.9 s; p < 0.05) and v90%Δ ( 10.1 ± 3.8 and 44.3 ± 6.3 s, p < 0.05). The BE-slope post IIST_v200m was faster than in v200 m and v90%Δ (-47.9 ± 14.6 vs. -33.0 ± 10.4 vs. -33.6 ± 13.8 ml kg-1, p < 0.01), and the total anerobic (AnaerTotal) demand was lower in IIST_v200 m (37.4 ± 9.4 ml kg-1) than in 200 m and 90%Δ (51.4 ± 9.4 and 46.2 ± 7.7 ml kg-1, p < 0.01). Finally, the τ1off was related to AnaerTotal in IIST_v200m, v200 m, and v90%Δ (r = 0.64, r = 0.61, and r = 0.64, p < 0.01). The initial phase of the V ˙ O 2 recovery profile provided different (although reliable) conditions for the estimate of V ˙ O 2 p e a k with BE procedures, which accounted for the moderate effect of anerobic release on V ˙ O 2 off-kinetics, but compromised exceptionally the V ˙ O 2 p e a k estimate in the 200-m single trial.

RESUMO

Maximal oxygen consumption (V̇O2max), physiological thresholds, and hemoglobin mass are strong predictors of endurance performance. High values of V̇O2max, maximal aerobic power (MAP), and power output at anaerobic thresholds are key variables in elite rowers. Endurance athletes often use altitude training as a strategy to improve performance. However, no clear evidence exists that training at natural altitude enhances sea-level performance in elite rowers. This study aimed to evaluate the effect of altitude training on rowing-performance parameters at sea level. The study was conducted on eleven rowers (Six females, five males) from the Chilean National Team during a 3-week moderate altitude training (∼2,900 m. a.s.l.) under the live high-train high (LHTH) model. It included a rowing ergometer maximal incremental test and blood analysis (pre and post-altitude). Gas exchange analysis was performed to measure V̇O2max, ventilatory thresholds (VTs) and rowing economy/efficiency (ECR/GE%). LHTL training improves performance-related variables at sea level (V̇Emax: 3.3% (95% CI, 1.2-5.5); hemoglobin concentration ([Hb]): 4.3% (95% CI, 1.7-6.9); hematocrit (%): 4.5% (95% CI, 0.9-8.2); RBC (red blood cells) count: 5.3% (95% CI, 2.3-8.2); power at VT2: 6.9% (95% CI, 1.7-12.1), V̇EVT2: 6.4% (95% CI, 0.4-12.4); power at VT1: 7.3% (95% CI, 1.3-13.3), V̇EVT1: 8.7% (95% CI, 1.6-15.8)) and economy/efficiency-related variables (ECRVT2: 5.3% (95% CI, -0.6 to -10.0); GE(%): 5.8% (95% CI, 0.8-10.7)). The LHTH training decreased breathing economy at MAP (-2.8% (95% CI, 0.1-5.6)), pVT2 (-9.3% (95% CI, -5.9 to -12.7)), and pVT1 (-9.3% (95% CI, -4.1 to -14.4)). Non-significant changes were found for V̇O2max and MAP. This study describes the effects of a 3-week moderate altitude (LHTH training) on performance and economy/efficiency-related variables in elite rowers, suggesting that it is an excellent option to induce positive adaptations related to endurance performance.

RESUMO

The prediction of running performance at different competitive distances is a challenge, since it can be influenced by several physiological, morphological and biomechanical factors. In experienced male runners heterogeneous for maximal oxygen uptake (VO2max), endurance running performance can be well predicted by several key parameters of aerobic fitness such as VO2max and its respective velocity (vVO2max), running economy, blood lactate response to exercise, oxygen uptake kinetics and critical velocity. However, for a homogeneous group of well-trained endurance runners, the relationship between aerobic fitness parameters and endurance running performance seems to be influenced by the duration of the race (i.e., middle vs. long). Although middle-distance and ultramarathon runners present high aerobic fitness levels, there is no accumulating evidence showing that the aerobic key parameters influence both 800-m and ultramarathon performance in homogeneous group of well-trained runners. The vVO2max seems to be the best predictor of performance for 1500 m. For 3000 m, both vVO2max and blood lactate response to exercise are the main predictors of performance. Finally, for long distance events (5000 m, 10,000 m, marathon and ultramarathon), blood lactate response seems to be main predictor of performance. The different limiting/determinants factors and/or training-induced changes in aerobic parameters can help to explain this time- or distance-dependent pattern.