Decrease of O(2) deficit is a potential factor in increased time to exhaustion after specific endurance training

Open Water Swimming in Elite Triathletes: Physiological and Biomechanical Determinants

This study aimed (i) to analyze the 1500 m open water swimming performance, (ii) to examine the associations between physiological and biomechanical variables with swimming performance, and (iii) to determine which variables can predict swimming performance in triathletes. Fourteen elite triathletes (23.4±3.8 y) performed a 1500 m test in open water swimming conditions. Swimming performance was assessed using World Aquatics Points Scoring, and data were obtained from the 1500 m open water swimming test. Heart rate, end-exercise oxygen uptake (EE˙VO2) and blood lactate concentrations were measured. The initial 250 m of the 1500 m swimming test presented the highest values of biomechanical variables in males (i. e. swimming speed, stroke rate (SR), length (SL), index (SI)). A decrease in SL was observed in the last 250 m in both sexes. Positive association were found between EE˙VO2 (r=0.513; p=0.030), swimming speed (r=0.873; p<0.001) and SI (r=0.704; p=0.002) with swimming performance. In contrast, time constant of the oxygen uptake (r=-0.500; p=0.034) and buoy-turn times (r=-0.525; p=0.027) were negatively associated with performance. SI was the main predictor (R 2=0.495) of open water swimming performance in triathletes. In conclusion, triathletes and coaches must conduct open water training sessions to maximize SI (i. e. swimming efficiency).

Oxygen Uptake and Bilaterally Measured Vastus Lateralis Muscle Oxygen Desaturation Kinetics in Well-Trained Endurance Cyclists

The aim of the present study was to compare and analyse the relationships between pulmonary oxygen uptake and vastus lateralis (VL) muscle oxygen desaturation kinetics measured bilaterally with Moxy NIRS sensors in trained endurance athletes. To this end, 18 trained athletes (age: 42.4 ± 7.2 years, height: 1.837 ± 0.053 m, body mass: 82.4 ± 5.7 kg) visited the laboratory on two consecutive days. On the first day, an incremental test was performed to determine the power values for the gas exchange threshold, the ventilatory threshold (VT), and V̇O_2max levels from pulmonary ventilation. On the second day, the athletes performed a constant work rate (CWR) test at the power corresponding to the VT. During the CWR test, the pulmonary ventilation characteristics, left and right VL muscle O₂ desaturation (DeSmO₂), and pedalling power were continuously recorded, and the average signal of both legs' DeSmO₂ was computed. Statistical significance was set at p ≤ 0.05. The relative response amplitudes of the primary and slow components of VL desaturation and pulmonary oxygen uptake kinetics did not differ, and the primary amplitude of muscle desaturation kinetics was strongly associated with the initial response rate of oxygen uptake. Compared with pulmonary O₂ kinetics, the primary response time of the muscle desaturation kinetics was shorter, and the slow component started earlier. There was good agreement between the time delays of the slow components describing global and local metabolic processes. Nevertheless, there was a low level of agreement between contralateral desaturation kinetic variables. The averaged DeSmO₂ signal of the two sides of the body represented the oxygen kinetics more precisely than the right- or left-leg signals separately.

Effects of wearing different face masks on cardiopulmonary performance at rest and exercise in a partially double-blinded randomized cross-over study

The use of face masks became mandatory during SARS-CoV-2 pandemic. Wearing masks may lead to complaints about laboured breathing and stress. The influence of different masks on cardiopulmonary performance was investigated in a partially double-blinded randomized cross-over design. Forty subjects (19-65 years) underwent body plethysmography, ergometry, cardiopulmonary exercise test and a 4-h wearing period without a mask, with a surgical mask (SM), a community mask (CM), and an FFP2 respirator (FFP2). Cardiopulmonary, physical, capnometric, and blood gas related parameters were recorded. Breathing resistance and work of breathing were significantly increased while wearing a mask. During exercise the increase in minute ventilation tended to be lower and breathing time was significantly longer with mask than without mask. Wearing a mask caused significant minimal decreases in blood oxygen pressure, oxygen saturation, an initial increase in blood and inspiratory carbon dioxide pressure, and a higher perceived physical exertion and temperature and humidity behind the mask under very heavy exercise. All effects were stronger when wearing an FFP2. Wearing face masks at rest and under exercise, changed breathing patterns in the sense of physiological compensation without representing a health risk. Wearing a mask for 4-h during light work had no effect on blood gases.

Low-volume HIIT and MICT speed V̇O2 kinetics during high-intensity "work-to-work" cycling with a similar time-course in type 2 diabetes

We assessed the rates of adjustment in oxygen uptake (V̇O₂) and muscle deoxygenation (i.e., deoxygenated haemoglobin and myoglobin, [HHb+Mb]) during the on-transition to high-intensity cycling initiated from an elevated baseline (work-to-work) before training and at weeks 3, 6, 9 and 12 of low-volume high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) in type 2 diabetes (T2D). Participants were randomly assigned to MICT (n=11, 50 min of moderate-intensity cycling), HIIT (n =8, 10x1 min of high-intensity cycling separated by 1-min of light cycling) or non-exercising control (n=9) groups. Exercising groups trained 3 times per week. Participants completed two work-to-work transitions at each time point consisting of sequential step increments to moderate- and high-intensity work-rates. [HHb+Mb] kinetics were measured by near-infrared spectroscopy at the vastus lateralis muscle. The pretraining time constant of the primary phase of V̇O₂ (V̇O₂τ_p) and the amplitude of the V̇O₂ slow component (V̇O₂A_s) of the high-intensity w-to-w bout decreased (P<0.05) by a similar magnitude at wk 3 of training in both MICT (from, 56±9 to 43±6s, and from 0.17±0.07 to 0.09±0.05 L.min^-1, respectively) and HIIT (from, 56±8 to 42±6s, and from 0.18±0.05 to 0.09±0.08 L.min^-1, respectively) with no further changes thereafter. No changes were reported in controls. The parameter estimates of Δ[HHb+Mb] remained unchanged in all groups. MICT and HIIT elicited comparable improvements in V̇O₂ kinetics without changes in muscle deoxygenation kinetics during high-intensity exercise initiated from an elevated baseline in T2D despite training volume and time commitment being ~50% lower in the HIIT group.

The Relationship between VO2 and Muscle Deoxygenation Kinetics and Upper Body Repeated Sprint Performance in Trained Judokas and Healthy Individuals

The present study sought to investigate if faster upper body oxygen uptake (VO₂) and hemoglobin/myoglobin deoxygenation ([HHb]) kinetics during heavy intensity exercise were associated with a greater upper body repeated-sprint ability (RSA) performance in a group of judokas and in a group of individuals of heterogenous fitness level. Eight judokas (JT) and seven untrained healthy participants (UT) completed an incremental step test, two heavy intensity square-wave transitions and an upper body RSA test consisting of four 15 s sprints, with 45 s rest, from which the experimental data were obtained. In the JT group, VO₂ kinetics, [HHb] kinetics and the parameters determined in the incremental test were not associated with RSA. However, when the two groups were combined, the amplitude of the primary phase VO₂ and [HHb] were positively associated with the accumulated work in the four sprints (ΣWork). Additionally, maximal aerobic power (MAP), peak VO₂ and the first ventilatory threshold (VT₁) showed a positive correlation with ΣWork and an inverse correlation with the decrease in peak power output (Dec-PPO) between the first and fourth sprints. Faster VO₂ and [HHb] kinetics do not seem to be associated with an increased upper body RSA in JT. However, other variables of aerobic fitness seem to be associated with an increased upper body RSA performance in a group of individuals with heterogeneous fitness level.

Effects of surgical masks on the responses to constant work-rate cycling performed at different intensity domains

We aimed at examining the impact of wearing surgical face masks on exercise performance. Thirty-two healthy adults (16 males and 16 females) completed a graded exercise test to measure peak oxygen uptake (VO_2peak ) and the ventilatory threshold (VT). Then, on separate days, all participants performed resting and standardized protocols (moderate intensity: 25% infra-VT; severe intensity: 25% supra-VT) on two different conditions (with and without a surgical mask). The use of masks reduced both VO₂ and minute ventilation during moderate and severe exercise (p < 0.0001), and this effect was particularly pronounced during severe exercise. Time to exhaustion was also shortened by ~10% on the face mask condition (p = 0.014). In contrast, neither heart rate nor the respiratory exchange ratio was affected by masking. The submaximal VO₂ was similar between the two epochs of analysis obtained during moderate cycling (i.e. 3-6 min vs. 7-10 min) and this occurred similarly between conditions. In conclusion, the impact of the surgical masks on exercise capacity is particularly pronounced during severe exercise performed at constant work rate. Ultimately, this may implicate a considerable impairment of structured or even unstructured strenuous physical activity. Clinical Trials registration number: NCT04963049.

Bioenergetic Mechanisms Linking V˙O2 Kinetics and Exercise Tolerance

We hypothesize that the V˙O2 time constant (τV˙O2) determines exercise tolerance by defining the power output associated with a "critical threshold" of intramuscular metabolite accumulation (e.g., inorganic phosphate), above which muscle fatigue and work inefficiency are apparent. Thereafter, the V˙O2 "slow component" and its consequences (increased pulmonary, circulatory, and neuromuscular demands) determine performance limits.

The Oxygen Uptake Plateau-A Critical Review of the Frequently Misunderstood Phenomenon

A flattening of the oxygen uptake–work rate relationship at severe exercise indicates the achievement of maximum oxygen uptake \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left({\text{VO}}_{2\max } \right)$$\end{document}VO2max. Unfortunately, a distinct plateau \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left( {{{\text{VO}}}_{2} {\text{pl}}} \right)$$\end{document}VO2pl at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{VO}}}_{2\max }$$\end{document}VO2maxis not found in all participants. The aim of this investigation was to critically review the influence of research methods and physiological factors on the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{VO}}}_{2} {\text{pl}}$$\end{document}VO2pl incidence. It is shown that many studies used inappropriate definitions or methodical approaches to check for the occurrence of a \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{VO}}}_{2} {\text{pl}}$$\end{document}VO2pl. In contrast to the widespread assumptions it is unclear whether there is higher \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{VO}}}_{2} {\text{pl}}$$\end{document}VO2pl incidence in (uphill) running compared to cycling exercise or in discontinuous compared to continuous incremental exercise tests. Furthermore, most studies that evaluated the validity of supramaximal verification phases, reported verification bout durations, which are too short to ensure that \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{VO}}}_{2\max }$$\end{document}VO2max have been achieved by all participants. As a result, there is little evidence for a higher \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{VO}}}_{2} {\text{pl}}$$\end{document}VO2pl incidence and a corresponding advantage for the diagnoses of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{VO}}}_{2\max }$$\end{document}VO2max when incremental tests are supplemented by supramaximal verification bouts. Preliminary evidence suggests that the occurrence of a \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{VO}}}_{2} {\text{pl}}$$\end{document}VO2pl in continuous incremental tests is determined by physiological factors like anaerobic capacity, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{VO}}}_{2}$$\end{document}VO2-kinetics and accumulation of metabolites in the submaximal intensity domain. Subsequent studies should take more attention to the use of valid \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{VO}}}_{2} {\text{pl}}$$\end{document}VO2pl definitions, which require a cut-off at ~ 50% of the submaximal \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{VO}}}_{2}$$\end{document}VO2 increase and rather large sampling intervals. Furthermore, if verification bouts are used to verify the achievement of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{VO}}}_{{2{\text{peak}}}}$$\end{document}VO2peak/\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\text{VO}}}_{2\max }$$\end{document}VO2max, it should be ensured that they can be sustained for sufficient durations.

The dose-response relationship between interval-training and VO2max in well-trained endurance runners: A systematic review

Success in endurance running is primarily determined by maximal aerobic power (VO_2max), fractional utilization, and running economy (RE). Within the literature, two training modalities have been identified to improve VO_2max; continuous training (CT) and interval-training (IT). The efficacy of IT to improve VO_2max in well-trained runners remains equivocal, as does whether a dose-response relationship exists between the IT training load performed and changes in VO_2max. A keyword search was performed in five electronic databases. Seven studies met the inclusion criteria for this systematic review. The training impulse (TRIMP) was calculated to analyse relationships between training load and changes in VO_2max, by calculating the time accumulated in certain intensity domains throughout a training intervention. Non-significant (P>0.05) improvements in VO_2max were reported in six studies, with only one study reporting a significant (P<0.05) improvement following the IT interventions. A relationship between the training session impulse of the interval-training performed (IT S_TRIMP) and VO_2max improvements were observed. The efficacy of IT to improve VO_2max in well-trained runners remains equivocal, nevertheless, the novel method of training-load analysis demonstrates a relationship between the IT S_TRIMP and VO_2max improvements. This provides practical application for the periodization of IT within the training regime of well-trained distance runners.

Oxygen uptake plateau occurrence depends on oxygen kinetics and oxygen deficit accumulation

We tested the hypothesis that participants with an oxygen uptake ( V ˙ O 2 ) plateau during incremental exercise exhibit a lower VO₂ -deficit (VO_2DEF )-accumulation in the submaximal intensity domain due to faster ramp and square wave O₂ -kinetics. Twenty-six male participants performed a standard ramp test (increment: 30 W·min^-1 ), a ramp test with an individualized ramp slope and a two-step (moderate and severe) square wave exercise followed by a V ˙ O 2 m a x -verification bout. VO_2DEF was calculated by the difference between individualized ramp test V ˙ O₂ and V ˙ O₂ -demand estimated from steady-state V ˙ O₂ -kinetics. Twenty-four participants verified their V ˙ O_2max in the verification test. Ten of them showed a plateau in the individualized ramp test. VO_2DEF at the end of this ramp test (4.34 ± 0.60 vs 4.54 ± 0.43 L) was not different between the plateau and the non-plateau group (P > 0.05). The plateau group had a significantly (P < 0.05) lower VO_2DEF 2 minutes before termination of the individualized ramp test (2.24 ± 0.40 vs 2.78 ± 0.33 L). This coincided with a shorter mean response time (43 ± 9 vs 53 ± 7 seconds), a higher increase in V ˙ O₂ per W (10.1 ± 0.2 vs 9.2 ± 0.5 mL·min^-1 ·W^-1 ) at the individualized ramp test as well as shorter time constants of moderate (36 ± 6 vs 48 ± 7 seconds) and severe (62 ± 9 vs 86 ± 10 seconds) square wave kinetics (all P < 0.05). We conclude that the V ˙ O₂ -plateau occurrence requires a fast V ˙ O₂ -kinetics and a low VO_2DEF -accumulation at intensities below V ˙ O_2max .

Elevated baseline work rate slows pulmonary oxygen uptake kinetics and decreases critical power during upright cycle exercise

Critical power is a fundamental parameter defining high-intensity exercise tolerance, and is related to the phase II time constant of pulmonary oxygen uptake kinetics (τV˙O2). Whether this relationship is causative is presently unclear. This study determined the impact of raised baseline work rate, which increases τV˙O2, on critical power during upright cycle exercise. Critical power was determined via four constant-power exercise tests to exhaustion in two conditions: (1) with exercise initiated from an unloaded cycling baseline (U→S), and (2) with exercise initiated from a baseline work rate of 90% of the gas exchange threshold (M→S). During these exercise transitions, τV˙O2 and the time constant of muscle deoxyhemoglobin kinetics (τ[HHb + Mb] ) (the latter via near-infrared spectroscopy) were determined. In M→S, critical power was lower (M→S = 203 ± 44 W vs. U→S = 213 ± 45 W, P = 0.011) and τV˙O2 was greater (M→S = 51 ± 14 sec vs. U→S = 34 ± 16 sec, P = 0.002) when compared with U→S. Additionally, τ[HHb + Mb] was greater in M→S compared with U→S (M→S = 28 ± 7 sec vs. U→S = 14 ± 7 sec, P = 0.007). The increase in τV˙O2 and concomitant reduction in critical power in M→S compared with U→S suggests a causal relationship between these two parameters. However, that τ[HHb + Mb] was greater in M→S exculpates reduced oxygen availability as being a confounding factor. These data therefore provide the first experimental evidence that τV˙O2 is an independent determinant of critical power. Keywords critical power, exercise tolerance, oxygen uptake kinetics, power-duration relationship, muscle deoxyhemoglobin kinetics, work-to-work exercise.

An "Exercise" in Cardiac Metabolism

Research has demonstrated that the high capacity requirements of the heart are satisfied by a preference for oxidation of fatty acids. However, it is well known that a stressed heart, as in pathological hypertrophy, deviates from its inherent profile and relies heavily on glucose metabolism, primarily achieved by an acceleration in glycolysis. Moreover, it has been suggested that the chronically lipid overloaded heart augments fatty acid oxidation and triglyceride synthesis to an even greater degree and, thus, develops a lipotoxic phenotype. In comparison, classic studies in exercise physiology have provided a basis for the acute metabolic changes that occur during physical activity. During an acute bout of exercise, whole body glucose metabolism increases proportionately to intensity while fatty acid metabolism gradually increases throughout the duration of activity, particularly during moderate intensity. However, the studies in chronic exercise training are primarily limited to metabolic adaptations in skeletal muscle or to the mechanisms that govern physiological signaling pathways in the heart. Therefore, the purpose of this review is to discuss the precise changes that chronic exercise training elicits on cardiac metabolism, particularly on substrate utilization. Although conflicting data exists, a pattern of enhanced fatty oxidation and normalization of glycolysis emerges, which may be a therapeutic strategy to prevent or regress the metabolic phenotype of the hypertrophied heart. This review also expands on the metabolic adaptations that chronic exercise training elicits in amino acid and ketone body metabolism, which have become of increased interest recently. Lastly, challenges with exercise training studies, which could relate to several variables including model, training modality, and metabolic parameter assessed, are examined.

Influence of Acetaminophen Consumption on Perceived Exertion at the Lactate Concentration Threshold

The purpose of this investigation was to study effects of acetaminophen consumption on ratings of perceived exertion and estimated time limit responses at the lactate threshold. 98 young regional to national level athletes performed a graded exhausting exercise on an outdoor running track to estimate their maximal aerobic velocity and the velocity associated with their lactate concentration threshold. Urine (30 mL) was collected during this test and analysed for numerous substances. During urinary screening for doping substances, 9 acetaminophen consumers (9.2%) among the 98 included athletes were detected. These acetaminophen consumers have significantly lower perceived exertion at velocity corresponding to the lactate concentration threshold than nonconsumers (11.9 ± 2.1 vs 13.6 ± 2.1, respectively) although they were at the same relative exercise intensity. This result shows that acetaminophen consumption may have mediated the perceived exertion response at the lactate concentration threshold. This may then suggest that the pain induced by training load could be a factor in use of self-prescribed pain relievers. Such consumption must be taken into account by medical staff, trainers, or educators who have to give information on the use and adverse effects of this substance and to propose palliative methods to their athletes.

Cardiorespiratory fitness and aerobic performance adaptations to a 4-week sprint interval training in young healthy untrained females

Purpose

The aim of this study was to test the effects of sprint interval training (SIT) on cardiorespiratory fitness and aerobic performance measures in young females.

Methods

Eight healthy, untrained females (age 21 ± 1 years; height 165 ± 5 cm; body mass 63 ± 6 kg) completed cycling peak oxygen uptake (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{V}{\text{O}}_{2} $$\end{document}V˙O2 peak), 10-km cycling time trial (TT) and critical power (CP) tests pre- and post-SIT. SIT protocol included 4 × 30-s “all-out” cycling efforts against 7 % body mass interspersed with 4 min of active recovery performed twice per week for 4 weeks (eight sessions in total).

Results

There was no significant difference in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{V}{\text{O}}_{2} $$\end{document}V˙O2 peak following SIT compared to the control period (control period: 31.7 ± 3.0 ml kg⁻¹ min⁻¹; post-SIT: 30.9 ± 4.5 ml kg⁻¹ min⁻¹; p > 0.05), but SIT significantly improved time to exhaustion (TTE) (control period: 710 ± 101 s; post-SIT: 798 ± 127 s; p = 0.00), 10-km cycling TT (control period: 1055 ± 129 s; post-SIT: 997 ± 110 s; p = 0.004) and CP (control period: 1.8 ± 0.3 W kg⁻¹; post-SIT: 2.3 ± 0.6 W kg⁻¹; p = 0.01).

Conclusions

These results demonstrate that young untrained females are responsive to SIT as measured by TTE, 10-km cycling TT and CP tests. However, eight sessions of SIT over 4 weeks are not enough to provide sufficient training stimulus to increase \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{V}{\text{O}}_{2} $$\end{document}V˙O2 peak.

Influence of the Type of Training Sport Practised on Psychological and Physiological Parameters during Exhausting Endurance Exercises

The present purpose was to study the influence of the type of training sport practised (long distance running, sprinting, handball) on ratings of perceived exertion (RPE), estimation of time limit (ETL), and heart rate (HR) on running tests. It was hypothesised that these parameters would be related to the type of training sport practised. 31 trained women (10 endurance-trained runners, 10 sprinters, and 11 handball players) performed two exercises to exhaustion on an outdoor track. The first test was a graded run to estimate maximal aerobic speed (SMA), i.e., the minimal speed which elicited maximal oxygen uptake. The second test was a constant all-out run at speed delta 50 (SΔ50), which corresponded to the speed halfway between SMA and the speed at lactate threshold (SLT), to specify time to exhaustion at this intensity (TLIM). Sensations regarding RPE, ETL, and HR were recorded during these tests. SMA, SΔ50, and SLT, expressed in absolute values (km · hr.−1) were statistically significantly different between groups ( p<.05) whereas TLIM was not. The covariance analysis showed that endurance-trained runners perceived the exercise as lighter and presented lower HR than handball players and sprinters for a same running %SMA ( p<.05). Moreover, endurance-trained runners felt that they could endure more than the other groups at a given %SMA or relative exhaustion time (%TLIM). These results mean that the type of training sport which has been performed may mediate perceptual responses and influence physiological parameters during exhausting exercises. These results are likely in part related to sport-specificity of the exercise mode used in tests. This point must be taken into consideration by physical trainers who have to prescribe exercise intensities during athletic seasons for different groups of athletes.

The oxygen uptake slow component at submaximal intensities in breaststroke swimming

The present work proposed to study the oxygen uptake slow component (VO2 SC) of breaststroke swimmers at four different intensities of submaximal exercise, via mathematical modeling of a multi-exponential function. The slow component (SC) was also assessed with two different fixed interval methods and the three methods were compared. Twelve male swimmers performed a test comprising four submaximal 300 m bouts at different intensities where all expired gases were collected breath by breath. Multi-exponential modeling showed values above 450 ml·min⁻¹ of the SC in the two last bouts of exercise (those with intensities above the lactate threshold). A significant effect of the method that was used to calculate the VO2 SC was revealed. Higher mean values were observed when using mathematical modeling compared with the fixed interval 3rd min method (F=7.111; p=0.012; η2=0.587); furthermore, differences were detected among the two fixed interval methods. No significant relationship was found between the SC determined by any method and the blood lactate measured at each of the four exercise intensities. In addition, no significant association between the SC and peak oxygen uptake was found. It was concluded that in trained breaststroke swimmers, the presence of the VO2 SC may be observed at intensities above that corresponding to the 3.5 mM-1 threshold. Moreover, mathematical modeling of the oxygen uptake on-kinetics tended to show a higher slow component as compared to fixed interval methods.

High-Intensity Cycling Training: The Effect of Work-to-Rest Intervals on Running Performance Measures

The work-to-rest ratio during cycling-based high-intensity interval training (HIT) could be important in regulating physiological and performance adaptations. We sought to determine the effectiveness of cycling-based HIT with different work-to-rest ratios for long-distance running. Thirty-two long-distance runners (age: 39 ± 8 years; sex: 14 men, 18 women; average weekly running training volume: 25 miles) underwent baseline testing (3-km time-trial, V[Combining Dot Above]O2peak and time to exhaustion, and Wingate test) before a 2-week matched-work cycling HIT of 6 × 10-second sprints with different rest periods (30 seconds [R30], 80 seconds [R80], 120 seconds [R120], or control). Three-kilometer time trial was significantly improved in the R30 group only (3.1 ± 4.0%, p = 0.04), whereas time to exhaustion was significantly increased in the 2 groups with a lower work-to-rest ratio (R30 group 6.4 ± 6.3%, p = 0.003 vs. R80 group 4.4 ± 2.7%, p = 0.03 vs. R120 group 1.9 ± 5.0%, p = 0.2). However, improvements in average power production were significantly greater with a higher work-to-rest ratio (R30 group 0.3 ± 4.1%, p = 0.8 vs. R80 group 4.6 ± 4.2%, p = 0.03 vs. R120 group 5.3 ± 5.9%, p = 0.02), whereas peak power significantly increased only in the R80 group (8.5 ± 8.2%, p = 0.04) but not in the R30 group (4.3 ± 6.1%, p = 0.3) or in the R120 group (7.1 ± 7.9%, p = 0.09). Therefore, cycling-based HIT is an effective way to improve running performance, and the type and magnitude of adaptation is dependent on the work-to-rest ratio.

Effects of ischemic preconditioning on maximal constant-load cycling performance

This study investigated the effects of ischemic preconditioning (IPC) on the ratings of perceived exertion (RPE), surface electromyography, and pulmonary oxygen uptake (V̇o2) onset kinetics during cycling until exhaustion at the peak power output attained during an incremental test. A group of 12 recreationally trained cyclists volunteered for this study. After determination of peak power output during an incremental test, they were randomly subjected on different days to a performance protocol preceded by intermittent bilateral cuff pressure inflation to 220 mmHg (IPC) or 20 mmHg (control). To increase data reliability, the performance visits were replicated, also in a random manner. There was an 8.0% improvement in performance after IPC (control: 303 s, IPC 327 s, factor SDs of ×/÷1.13, P = 0.01). This change was followed by a 2.9% increase in peak V̇o2 (control: 3.95 l/min, IPC: 4.06 l/min, factor SDs of ×/÷1.15, P = 0.04), owing to a higher amplitude of the slow component of the V̇o2 kinetics (control: 0.45 l/min, IPC: 0.63 l/min, factor SDs of ×/÷2.21, P = 0.05). There was also an attenuation in the rate of increase in RPE ( P = 0.01) and a progressive increase in the myoelectrical activity of the vastus lateralis muscle ( P = 0.04). Furthermore, the changes in peak V̇o2 ( r = 0.73, P = 0.007) and the amplitude of the slow component ( r = 0.79, P = 0.002) largely correlated with performance improvement. These findings provide a link between improved aerobic metabolism and enhanced severe-intensity cycling performance after IPC. Furthermore, the delayed exhaustion after IPC under lower RPE and higher skeletal muscle activation suggest they have a role on the ergogenic effects of IPC on endurance performance.

Unchanged content of oxidative enzymes in fast-twitch muscle fibers and V˙O2 kinetics after intensified training in trained cyclists

The present study examined if high intensity training (HIT) could increase the expression of oxidative enzymes in fast-twitch muscle fibers causing a faster oxygen uptake () response during intense (INT), but not moderate (MOD), exercise and reduce the slow component and muscle metabolic perturbation during INT. Pulmonary kinetics was determined in eight trained male cyclists (-max: 59 ± 4 (means ± SD) mL min⁻¹ kg⁻¹) during MOD (205 ± 12 W ∼65% -max) and INT (286 ± 17 W ∼85% -max) exercise before and after a 7-week HIT period (30-sec sprints and 4-min intervals) with a 50% reduction in volume. Both before and after HIT the content in fast-twitch fibers of CS (P < 0.05) and COX-4 (P < 0.01) was lower, whereas PFK was higher (P < 0.001) than in slow-twitch fibers. Content of CS, COX-4, and PFK in homogenate and fast-twitch fibers was unchanged with HIT. Maximal activity (μmol g DW⁻¹ min⁻¹) of CS (56 ± 8 post-HIT vs. 59 ± 10 pre-HIT), HAD (27 ± 6 vs. 29 ± 3) and PFK (340 ± 69 vs. 318 ± 105) and the capillary to fiber ratio (2.30 ± 0.16 vs. 2.38 ± 0.20) was unaltered following HIT. kinetics was unchanged with HIT and the speed of the primary response did not differ between MOD and INT. Muscle creatine phosphate was lower (42 ± 15 vs. 66 ± 17 mmol kg DW⁻¹) and muscle lactate was higher (40 ± 18 vs. 14 ± 5 mmol kg DW⁻¹) at 6 min of INT (P < 0.05) after compared to before HIT. A period of intensified training with a volume reduction did not increase the content of oxidative enzymes in fast-twitch fibers, and did not change kinetics.

Endurance training facilitates myoglobin desaturation during muscle contraction in rat skeletal muscle

At onset of muscle contraction, myoglobin (Mb) immediately releases its bound O₂ to the mitochondria. Accordingly, intracellular O₂ tension (P_mbO₂) markedly declines in order to increase muscle O₂ uptake (mO₂). However, whether the change in P_mbO₂ during muscle contraction modulates mO₂ and whether the O₂ release rate from Mb increases in endurance-trained muscles remain unclear. The purpose of this study was, therefore, to determine the effect of endurance training on O₂ saturation of Mb (S_mbO₂) and P_mbO₂ kinetics during muscle contraction. Male Wistar rats were subjected to a 4-week swimming training (Tr group; 6 days per week, 30 min × 4 sets per day) with a weight load of 2% body mass. After the training period, deoxygenated Mb kinetics during muscle contraction were measured using near-infrared spectroscopy under hemoglobin-free medium perfusion. In the Tr group, the mO₂peak significantly increased by 32%. Although the P_mbO₂ during muscle contraction did not affect the increased mO₂ in endurance-trained muscle, the O₂ release rate from Mb increased because of the increased Mb concentration and faster decremental rate in S_mbO₂ at the maximal twitch tension. These results suggest that the Mb dynamics during muscle contraction are contributing factors to faster O₂ kinetics in endurance-trained muscle.

[Muscle retraining or aerobic endurance training? What will improve the aerobic capacity of patients with coronary disease in the only 4 weeks?]

OBJECTIVE

The aim of this study was to compare the effects of 4 weeks of CT and AT, which training impulse (total external workload and perceived exertion), are similar on power associated at VO2 peak (pVO2 peak) and cardiorespiratory responses of patient with CAD.

METHOD

Eighteen male with CAD (62 ± 7 years, 175 ± 2 cm, 84 ± 16 kg, fraction of ejection = 0.49 ± 0.16) performed 4 weeks of CT (n = 9) or AT (n = 9). pVO2 peak, maximal and first ventilatory threshold values of oxygen uptake (VO2 peak, VO2-vt) and heart rate (HRmax, HR-vt) were measured before and after training session. Total training impulse (exercise rehabilitation and other paramedical actions) were evaluated and harmonized between AT and CT according to Foster et al. formula (1996) RESULTS: No significant difference were found in training impulse between AT and CT (3650 ± 220 vs 3497 ± 190 U, P = NS). VO2 pic increased after AT (16.9 ± 4.4 vs 18.9 ± 4.9 mL O2/min/kg, P < 0.05) and remained unchanged after CT (17.7 ± 7.8 vs 17.8 ± 7.2, P = NS). Four weeks of training induced significant increase in pVO2 peak, VO2-vt and FC-vt, expressed in absolute or relative value (P < 0,05), without any difference between AT and CT modalities (P = NS).

CONCLUSIONS

Improving pVO2 pic following an exercise training does not necessarily preclude an improvement in coronary VO2 pic. pVO2 peak was not improved with the same cardiorespiratory adaptations between AT and CT. Thus, there seems important to measure gas exchanges of subject with CAD during the incremental test and identify the respective part of muscular and cardiorespiratory functions in exercise exhaustion.

Effects of high-intensity running training on soccer-specific fitness in professional male players

The purpose of this study was to investigate whether or not physiological and performance gains could be achieved with the addition of high-intensity running to an existing training programme in a group of well trained professional male soccer players. Sixteen professional male players (21.3 ± 2.1 years, stature 177.4 ± 4.2 cm, body mass 73.1 ± 8.1 kg) were randomised in training (TRA, n = 8) and control (CON, n = 8) groups. All players performed physiological assessments before and after a 6-week intervention. Outcome measures were: (i) V̇O2peak, (ii) V̇O2 kinetics during very heavy-intensity exercise, (iii) a maximal anaerobic running test, and (iv) Yo-Yo Intermittent Recovery Test level 2 (YIRT2). The only aerobic parameter to change after the intervention was the phase III time constant at exercise onset for CON, which lengthened (p = 0.012) to a value similar to that of the TRA group. However, TRA showed gains in anaerobic performance (p = 0.021), time to exhaustion (p = 0.019), and maximal running speed (p = 0.023). In the YIRT2, distance run increased for TRA over time (p = 0.015), and the TRA group were also capable of running further in the YIRT2 after the intervention compared with CON (p = 0.011). This study shows it is possible to improve the soccer-specific high-intensity running capacity of professional players when high-intensity intermittent training is added to the normal training load and that this effect is only detectable in anaerobic capabilities. The observed effects are meaningful to the training practices of elite athletes seeking a competitive edge in team sports when otherwise well matched.

Effects of interval and continuous training on O2 uptake kinetics during severe-intensity exercise initiated from an elevated metabolic baseline

The purpose of this study was to test the hypothesis that V̇o2 kinetics would be speeded to a greater extent following repeated sprint training (RST), compared with continuous endurance training (ET), in the transition from moderate- to severe-intensity exercise. Twenty-three recreationally active subjects were randomly assigned to complete six sessions of ET (60–110 min of moderate-intensity cycling) or RST (four to seven 30-s all-out Wingate tests) over a 2-wk period. Subjects completed three identical work-to-work cycling exercise tests before and after the intervention period, consisting of baseline cycling at 20 W followed by sequential step increments to moderate- and severe-intensity work rates. The severe-intensity bout was continued to exhaustion on one occasion and was followed by a 60-s all-out sprint on another occasion. Phase II pulmonary V̇o2 kinetics were speeded by a similar magnitude in both the lower (ET pre, 28 ± 4; ET post, 22 ± 4 s; RST pre, 25 ± 8; RST post, 20 ± 7 s) and upper (ET pre, 50 ± 10; ET post, 39 ± 11 s; RST pre, 54 ± 7; RST post, 40 ± 11 s) steps of the work-to-work test following ET and RST ( P < 0.05). The tolerable duration of exercise and the total amount of sprint work completed in the exercise performance test were also similarly enhanced by ET and RST ( P < 0.05). Therefore, ET and RST provoked comparable improvements in V̇o2 kinetics and exercise performance in the transition from an elevated baseline work rate, with RST being a more time-efficient approach to elicit these adaptations.

Effects of beta-alanine supplementation and interval training on physiological determinants of severe exercise performance

INTRODUCTION

We aimed to manipulate physiological determinants of severe exercise performance. We hypothesized that (1) beta-alanine supplementation would increase intramuscular carnosine and buffering capacity and dampen acidosis during severe cycling, (2) that high-intensity interval training (HIT) would enhance aerobic energy contribution during severe cycling, and (3) that HIT preceded by beta-alanine supplementation would have greater benefits.

METHODS

Sixteen active men performed incremental cycling tests and 90-s severe (110 % peak power) cycling tests at three time points: before and after oral supplementation with either beta-alanine or placebo, and after an 11-days HIT block (9 sessions, 4 × 4 min), which followed supplementation. Carnosine was assessed via MR spectroscopy. Energy contribution during 90-s severe cycling was estimated from the O2 deficit. Biopsies from m. vastus lateralis were taken before and after the test.

RESULTS

Beta-alanine increased leg muscle carnosine (32 ± 13 %, d = 3.1). Buffering capacity and incremental cycling were unaffected, but during 90-s severe cycling, beta-alanine increased aerobic energy contribution (1.4 ± 1.3 %, d = 0.5), concurrent with reduced O2 deficit (-5.0 ± 5.0 %, d = 0.6) and muscle lactate accumulation (-23 ± 30 %, d = 0.9), while having no effect on pH. Beta-alanine also enhanced motivation and perceived state during the HIT block. There were no between-group differences in adaptations to the training block, namely increased buffering capacity (+7.9 ± 11.9 %, p = 0.04, d = 0.6, n = 14) and glycogen storage (+30 ± 47 %, p = 0.04, d = 0.5, n = 16).

CONCLUSIONS

Beta-alanine did not affect buffering considerably, but has beneficial effects on severe exercise metabolism as well as psychological parameters during intense training phases.

Oxygen uptake kinetics

Muscular exercise requires transitions to and from metabolic rates often exceeding an order of magnitude above resting and places prodigious demands on the oxidative machinery and O2-transport pathway. The science of kinetics seeks to characterize the dynamic profiles of the respiratory, cardiovascular, and muscular systems and their integration to resolve the essential control mechanisms of muscle energetics and oxidative function: a goal not feasible using the steady-state response. Essential features of the O2 uptake (VO2) kinetics response are highly conserved across the animal kingdom. For a given metabolic demand, fast VO2 kinetics mandates a smaller O2 deficit, less substrate-level phosphorylation and high exercise tolerance. By the same token, slow VO2 kinetics incurs a high O2 deficit, presents a greater challenge to homeostasis and presages poor exercise tolerance. Compelling evidence supports that, in healthy individuals walking, running, or cycling upright, VO2 kinetics control resides within the exercising muscle(s) and is therefore not dependent upon, or limited by, upstream O2-transport systems. However, disease, aging, and other imposed constraints may redistribute VO2 kinetics control more proximally within the O2-transport system. Greater understanding of VO2 kinetics control and, in particular, its relation to the plasticity of the O2-transport/utilization system is considered important for improving the human condition, not just in athletic populations, but crucially for patients suffering from pathologically slowed VO2 kinetics as well as the burgeoning elderly population.

Exercise: Kinetic considerations for gas exchange

The activities of daily living typically occur at metabolic rates below the maximum rate of aerobic energy production. Such activity is characteristic of the nonsteady state, where energy demands, and consequential physiological responses, are in constant flux. The dynamics of the integrated physiological processes during these activities determine the degree to which exercise can be supported through rates of O₂ utilization and CO₂ clearance appropriate for their demands and, as such, provide a physiological framework for the notion of exercise intensity. The rate at which O₂ exchange responds to meet the changing energy demands of exercise--its kinetics--is dependent on the ability of the pulmonary, circulatory, and muscle bioenergetic systems to respond appropriately. Slow response kinetics in pulmonary O₂ uptake predispose toward a greater necessity for substrate-level energy supply, processes that are limited in their capacity, challenge system homeostasis and hence contribute to exercise intolerance. This review provides a physiological systems perspective of pulmonary gas exchange kinetics: from an integrative view on the control of muscle oxygen consumption kinetics to the dissociation of cellular respiration from its pulmonary expression by the circulatory dynamics and the gas capacitance of the lungs, blood, and tissues. The intensity dependence of gas exchange kinetics is discussed in relation to constant, intermittent, and ramped work rate changes. The influence of heterogeneity in the kinetic matching of O₂ delivery to utilization is presented in reference to exercise tolerance in endurance-trained athletes, the elderly, and patients with chronic heart or lung disease.

High-intensity interval training speeds the adjustment of pulmonary O2 uptake, but not muscle deoxygenation, during moderate-intensity exercise transitions initiated from low and elevated baseline metabolic rates

During step transitions in work rate (WR) within the moderate-intensity (MOD) exercise domain, pulmonary O2 uptake (Vo2p) kinetics are slowed, and Vo2p gain (ΔVo2p/ΔWR) is greater when exercise is initiated from an elevated metabolic rate. High-intensity interval training (HIT) has been shown to speed Vo2p kinetics when step transitions to MOD exercise are initiated from light-intensity baseline metabolic rates. The effects of HIT on step transitions initiated from elevated metabolic rates have not been established. Therefore, this study investigated the effects of HIT on Vo2p kinetics during transitions from low and elevated metabolic rates, within the MOD domain. Eight young, untrained men completed 12 sessions of HIT (spanning 4 wk). HIT consisted of 8-12 1-min intervals, cycling at a WR corresponding to 110% of pretraining maximal WR (WRmax). Pre-, mid- and posttraining, subjects completed a ramp-incremental test to determine maximum O2 uptake, WRmax, and estimated lactate threshold (θL). Participants additionally completed double-step constant-load tests, consisting of step transitions from 20 W → Δ45% θL [lower step (LS)] and Δ45 → 90% θL [upper step (US)]. HIT led to increases in maximum O2 uptake (P < 0.05) and WRmax (P < 0.01), and τVo2p of both lower and upper MOD step transitions were reduced by ∼40% (LS: 24 s → 15 s; US: 45 s → 25 s) (P < 0.01). However, the time course of adjustment of local muscle deoxygenation was unchanged in the LS and US. These results suggest that speeding of Vo2p kinetics in both the LS and US may be due, in part, to an improved matching of muscle O2 utilization to microvascular O2 delivery within the working muscle following 12 sessions of HIT, although muscle metabolic adaptations cannot be discounted.

VO2 kinetics and performance in soccer players after intense training and inactivity

PURPOSE

The study's purpose was to examine the effects of a short-term period with intensified training or training cessation of trained soccer players on VO(2) kinetics at 75% maximal aerobic speed, oxidative enzymes, and performance in repeated high-intensity exercise.

METHODS

After the last match of the season, 18 elite soccer players were, for a 2-wk period, assigned to a high-intensity training group (n = 7) performing 10 training sessions mainly consisting of aerobic high-intensity training (8 × 2 min) and speed endurance training (10-12 × 30-s sprints) or a training cessation group (n = 11) that refrained from training.

RESULTS

For the training cessation group, VO(2) kinetics became slower (P < 0.05) with a larger time constant (τ = 21.5 ± 2.9 vs 23.8 ± 3.2 s (mean ± SD, before vs after)) and a larger mean response time (time delay + τ = 45.0 ± 1.8 vs 46.8 ± 2.2 s). The amount of muscle pyruvate dehydrogenase (17%, P < 0.01) and maximal activity of citrate synthase (12%) and 3-hydroxyacyl-CoA (18%, P < 0.05) were lowered. In addition, the fraction of slow twitch fibers (56% ± 18% vs 47% ± 15%, P < 0.05), Yo-Yo intermittent recovery level 2 test (845 ± 160 vs 654 ± 99 m), and the repeated sprint performance (33.41 ± 0.96 vs 34.11 ± 0.92 s, P < 0.01) were reduced. For the high-intensity training group, running economy was improved (P < 0.05), and the amount of pyruvate dehydrogenase (17%) and repeated sprint performance (33.44 ± 1.17 vs 32.81 ± 1.01 s) were enhanced (P < 0.05).

CONCLUSIONS

Inactivity slows VO(2) kinetics in association with a reduction of muscle oxidative capacity and repeated high-intensity running performance. In addition, intensified training of already well-trained athletes can improve mechanical efficiency and repeated sprint performance.

Blood lactate concentration at the maximal lactate steady state is not dependent on endurance capacity in healthy recreationally trained individuals

The aim of the study was to investigate the independent relationship between maximal lactate steady state (MLSS), blood lactate concentration [La] and exercise performance as reported frequently. Sixty-two subjects with a wide range of endurance performance (MLSS power output 199 ± 55 W; range: 100-302 W) were tested on an electronically braked cycle ergometer. One-min incremental exercise tests were conducted to determine maximal variables as well as the respiratory compensation point (RCP) and the second lactate turn point (LTP2). Several continuous exercise tests were performed to determine the MLSS. Subjects were divided into three clusters of exercise performance. Dietary control was employed throughout all testing. No significant correlation was found between MLSS [La] and power output at MLSS. Additionally, the three clusters of subjects with different endurance performance levels based on power output at MLSS showed no significant difference for MLSS [La]. MLSS [La] was not significantly different between men and women (average of 4.80 ± 1.50 vs. 5.22 ± 1.52 mmol l(-1)). MLSS [La] was significantly related to [La] at RCP, LTP2 and at maximal power. The results of this study support previous findings that MLSS [La] is independent of endurance performance. Additionally, MLSS [La] was not influenced by sex. Correlations found between MLSS [La] and [La] at maximal power and at designated anaerobic thresholds indicate only an association of [La] response during incremental and MLSS exercise when utilizing cycle ergometry.

Oxygen uptake kinetics and middle distance swimming performance

OBJECTIVE

The aim of this study was to determine whether V˙O(2) kinetics and specifically, the time constant of transitions from rest to heavy (τ(p)H) and severe (τ(p)S) exercise intensities, are related to middle distance swimming performance.

DESIGN

Fourteen highly trained male swimmers (mean ± SD: 20.5 ± 3.0 yr; 75.4 ± 12.4 kg; 1.80 ± 0.07 m) performed an discontinuous incremental test, as well as square wave transitions for heavy and severe swimming intensities, to determine V˙O(2) kinetics parameters using two exponential functions.

METHODS

All the tests involved front-crawl swimming with breath-by-breath analysis using the Aquatrainer swimming snorkel. Endurance performance was recorded as the time taken to complete a 400 m freestyle swim within an official competition (T400), one month from the date of the other tests.

RESULTS

T400 (Mean ± SD) (251.4 ± 12.4 s) was significantly correlated with τ(p)H (15.8 ± 4.8s; r=0.62; p=0.02) and τ(p)S (15.8 ± 4.7s; r=0.61; p=0.02). The best single predictor of 400 m freestyle time, out of the variables that were assessed, was the velocity at V˙O(2max)vV˙O(2max), which accounted for 80% of the variation in performance between swimmers. However, τ(p)H and V˙O(2max) were also found to influence the prediction of T400 when they were included in a regression model that involved respiratory parameters only.

CONCLUSIONS

Faster kinetics during the primary phase of the V˙O(2) response is associated with better performance during middle-distance swimming. However, vV˙O(2max) appears to be a better predictor of T400.

Pulmonary O2 uptake kinetics as a determinant of high-intensity exercise tolerance in humans

Tolerance to high-intensity constant-power (P) exercise is well described by a hyperbola with two parameters: a curvature constant (W') and power asymptote termed "critical power" (CP). Since the ability to sustain exercise is closely related to the ability to meet the ATP demand in a steady state, we reasoned that pulmonary O(2) uptake (Vo(2)) kinetics would relate to the P-tolerable duration (t(lim)) parameters. We hypothesized that 1) the fundamental time constant (τVo(2)) would relate inversely to CP; and 2) the slow-component magnitude (ΔVo(2sc)) would relate directly to W'. Fourteen healthy men performed cycle ergometry protocols to the limit of tolerance: 1) an incremental ramp test; 2) a series of constant-P tests to determine Vo(2max), CP, and W'; and 3) repeated constant-P tests (WR(6)) normalized to a 6 min t(lim) for τVo(2) and ΔVo(2sc) estimation. The WR(6) t(lim) averaged 365 ± 16 s, and Vo(2max) (4.18 ± 0.49 l/min) was achieved in every case. CP (range: 171-294 W) was inversely correlated with τVo(2) (18-38 s; R(2) = 0.90), and W' (12.8-29.9 kJ) was directly correlated with ΔVo(2sc) (0.42-0.96 l/min; R(2) = 0.76). These findings support the notions that 1) rapid Vo(2) adaptation at exercise onset allows a steady state to be achieved at higher work rates compared with when Vo(2) kinetics are slower; and 2) exercise exceeding this limit initiates a "fatigue cascade" linking W' to a progressive increase in the O(2) cost of power production (Vo(2sc)), which, if continued, results in attainment of Vo(2max) and exercise intolerance. Collectively, these data implicate Vo(2) kinetics as a key determinant of high-intensity exercise tolerance in humans.

Is acute static stretching able to reduce the time to exhaustion at power output corresponding to maximal oxygen uptake?

This study analyzed the effect of an acute static stretching bout on the time to exhaustion (Tlim) at power output corresponding to VO2max. Eleven physically active male subjects (age 22.3+/-2.8 years, VO2max 2.7+/-0.5 L.min) completed an incremental cycle ergometer test, 2 muscle strength tests, and 2 maximal tests to exhaustion at power output corresponding to VO2max with and without a previous static stretching bout. The Tlim was not significantly affected by the static stretching (164+/-28 vs. 150+/-26 seconds with and without stretching, respectively, p=0.09), but the time to reach VO2max (118+/-22 vs. 102+/-25 seconds), blood-lactate accumulation immediately after exercise (10.7+/-2.9 vs. 8.0+/-1.7 mmol.L), and oxygen deficit (2.4+/-0.9 vs. 2.1+/-0.7 L) were significantly reduced (p<or=0.02). Thus, an acute static stretching bout did not reduce Tlim at power output corresponding to VO2max possibly by accelerating aerobic metabolism activation at the beginning of exercise. These results suggest that coaches and practitioners involved with aerobic dependent activities may use static stretching as part of their warm-up routines without fear of diminishing high-intensity aerobic exercise performance.

Oxygen uptake kinetics during exercise in adults with Down syndrome

Persons with Down syndrome (DS) have diminished submaximal and peak work capacity. This study evaluated the dynamic response of oxygen uptake at onset and recovery (VO(2) kinetics) of constant-load exercise (moderate intensity 45% VO(2peak)) in adults with DS. A total of 27 healthy participants aged 18-50 years performed graded treadmill exercise to assess peak VO(2): 14 with DS (9 males and 5 females) and 13 controls without disabilities (9 males and 4 females). Subjects also performed constant-load exercise tests at 45% VO(2peak) to determine VO(2) on-transient and VO(2) off-transient responses. Peak VO(2) was lower in participants with DS as compared to controls (DS 30.2 ± 7.1; controls 46.1 ± 9.6 mL kg(-1) min(-1), P < 0.05). In contrast, at 45% VO(2peak), the time constants for the VO(2) on-transients (DS 34.6 ± 9.1; controls 37.6 ± 9.0 s) and VO(2) off-transients (DS 36.5 ± 12.3; controls 37.7 ± 7.0 s) were not significantly different between the groups. Additionally, there were no differences between on-transient and off-transient time constants in participants with DS or controls. These data demonstrate that the VO(2) kinetics at onset and recovery of moderate intensity exercise is similar between adults with DS and controls. Therefore, the submaximal exercise performance of these individuals is not affected by slowed VO(2) kinetics.

Physiological determinants of Yo-Yo intermittent recovery tests in male soccer players

The physiological determinants of performance in two Yo-Yo intermittent recovery tests (Yo-YoIR1 and Yo-YoIR2) were examined in 25 professional (n = 13) and amateur (n = 12) soccer players. The aims of the study were (1) to examine the differences in physiological responses to Yo-YoIR1 and Yo-YoIR2, (2) to determine the relationship between the aerobic and physiological responses to standardized high-intensity intermittent exercise (HIT) and Yo-Yo performance, and (3) to investigate the differences between professional and amateur players in performance and responses to these tests. All players performed six tests: two versions of the Yo-Yo tests, a test for the determination of maximum oxygen uptake (V(O)(2)(max)), a double test to determine V(O)(2) kinetics and a HIT evaluation during which several physiological responses were measured. The anaerobic contribution was greatest during Yo-YoIR2. V(O)(2)(max) was strongly correlated with Yo-YoIR1 (r = 0.74) but only moderately related to Yo-YoIR2 (r = 0.47). The time constant (tau) of V(O)(2) kinetics was largely related to both Yo-Yo tests (Yo-YoIR1: r = 0.60 and Yo-YoIR2: r = 0.65). The relationships between physiological variables measured during HIT (blood La(-), H(+), HCO(3) (-) and the rate of La(-) accumulation) and Yo-Yo performance (in both versions) were very large (r > 0.70). The physiological responses to HIT and the tau of the V(O)(2) kinetics were significantly different between professional and amateur soccer players, whilst V(O)(2)(max) was not significantly different between the two groups. In conclusion, V(O)(2)(max) is more important for Yo-YoIR1 performance, whilst tau of the V(O)(2) kinetics and the ability to maintain acid-base balance are important physiological factors for both Yo-Yo tests.

Influence of repeated sprint training on pulmonary O2 uptake and muscle deoxygenation kinetics in humans

We hypothesized that a short-term training program involving repeated all-out sprint training (RST) would be more effective than work-matched, low-intensity endurance training (ET) in enhancing the kinetics of oxygen uptake (V̇o2) and muscle deoxygenation {deoxyhemoglobin concentration ([HHb])} following the onset of exercise. Twenty-four recreationally active subjects (15 men, mean ± SD: age 21 ± 4 yr, height 173 ± 9 cm, body mass 71 ± 11 kg) were allocated to one of three groups: RST, which completed six sessions of four to seven 30-s RSTs; ET, which completed six sessions of work-matched, moderate-intensity cycling; and a control group (CON). All subjects completed moderate-intensity and severe-intensity “step” exercise transitions before (Pre) and after the 2-wk intervention period (Post). Following RST, [HHb] kinetics were speeded, and the amplitude of the [HHb] response was increased during both moderate and severe exercise ( P < 0.05); the phase II V̇o2 kinetics were accelerated for both moderate (Pre: 28 ± 8, Post: 21 ± 8 s; P < 0.01) and severe (Pre: 29 ± 5, Post: 23 ± 5 s; P < 0.05) exercise; the amplitude of the V̇o2 slow component was reduced (Pre: 0.52 ± 0.19, Post: 0.40 ± 0.17 l/min; P < 0.01); and exercise tolerance during severe exercise was improved by 53% (Pre: 700 ± 234, Post: 1,074 ± 431 s; P < 0.01). None of these parameters was significantly altered in the ET and CON groups. Six sessions of RST, but not ET, resulted in changes in [HHb] kinetics consistent with enhanced fractional muscle O2 extraction, faster V̇o2 kinetics, and an increased tolerance to high-intensity exercise.

Modeling energy expenditure and oxygen consumption in human exposure models: accounting for fatigue and EPOC

Human exposure and dose models often require a quantification of oxygen consumption for a simulated individual. Oxygen consumption is dependent on the modeled individual's physical activity level as described in an activity diary. Activity level is quantified via standardized values of metabolic equivalents of work (METS) for the activity being performed and converted into activity-specific oxygen consumption estimates. However, oxygen consumption remains elevated after a moderate- or high-intensity activity is completed. This effect, which is termed excess post-exercise oxygen consumption (EPOC), requires upward adjustment of the METS estimates that follow high-energy expenditure events, to model subsequent increased ventilation and intake dose rates. In addition, since an individual's capacity for work decreases during extended activity, methods are also required to adjust downward those METS estimates that exceed physiologically realistic limits over time. A unified method for simultaneously performing these adjustments is developed. The method simulates a cumulative oxygen deficit for each individual and uses it to impose appropriate time-dependent reductions in the METS time series and additions for EPOC. The relationships between the oxygen deficit and METS limits are nonlinear and are derived from published data on work capacity and oxygen consumption. These modifications result in improved modeling of ventilation patterns, and should improve intake dose estimates associated with exposure to airborne environmental contaminants.

Modeling and analysis of the effect of training on V O2 kinetics and anaerobic capacity

In this paper, we present an application of a number of tools and concepts for modeling and analyzing raw, unaveraged, and unedited breath-by-breath oxygen uptake data. A method for calculating anaerobic capacity is used together with a model, in the form of a set of coupled nonlinear ordinary differential equations to make predictions of the VO(2) kinetics, the time to achieve a percentage of a certain constant oxygen demand, and the time limit to exhaustion at intensities other than those in which we have data. Speeded oxygen kinetics and increased time limit to exhaustion are also investigated using the eigenvalues of the fixed points of our model. We also use a way of analyzing the oxygen uptake kinetics using a plot of V O(2)(t) vs V O(2)(t) which allows one to observe both the fixed point solutions and also the presence of speeded oxygen kinetics following training. A method of plotting the eigenvalue versus oxygen demand is also used which allows one to observe where the maximum amplitude of the so-called slow component will be and also how training has changed the oxygen uptake kinetics by changing the strength of the attracting fixed point for a particular demand.

Relationships between pulmonary oxygen uptake kinetics and other measures of aerobic fitness in middle- and long-distance runners

The purpose of this study was to assess the relationships between on- and off-transient pulmonary oxygen uptake kinetics and other measures of aerobic fitness in middle-distance (MD) and long-distance (LD) runners. 16 MD and 16 LD runners participated and each completed a series of tests to determine their maximal oxygen uptake (VO2max) gas-exchange threshold (GET), running economy (RE) and the primary time-constant for VO2 at the onset (tau(on)) and offset (tau(off)) of moderate-intensity treadmill exercise. Relationships between measures were established using Pearson product moment correlations (r). The relationships between VO2 kinetic parameter and other aerobic measures varied depending on classification of runner (MD or LD runner). There was a significant relationship between (VO2max) and tau(on) and tau(off) in LD runners (tau(on): r = -0.70, P = 0.003; tau(off): r = -0.55, P = 0.029), but not for MD (tau(on): r = 0.24, P = 0.366; tau(off): r = -0.09, P = 0.739). Similar relationships also existed between GET, RE and kinetic parameters for LD but not MD runners. The inconsistent relationships between VO2 kinetic parameters and other measures of aerobic fitness in MD and LD runners is intriguing. Further work is now required to identify how the volume and intensity of training influence peripheral adaptations in Type I and Type II fibres and how these may, or may not influence VO2 kinetic responses in the moderate- and heavy-intensity domain.

Effect of high-intensity interval training and detraining on extra $${\dot{{V}}\hbox{O}_{2}}$$ and on the $${\dot{{V}}\hbox{O}_{2}}$$ slow component

To examine the effect of 6-week of high-intensity interval training (HIT) and of 6-week of detraining on the VO2/Work Rate (WR) relationship and on the slow component of VO2, nine young male adults performed on cycle ergometer, before, after training and after detraining, an incremental exercise (IE), and a 6-min constant work rate exercise (CWRE) above the first ventilatory threshold (VT1). For each IE, the slope and the intercept of the VO2/WR relationship were calculated with linear regression using data before VT1. The difference between VO2max measured and VO2max expected using the pre-VT1 slope was calculated (extra VO2). The difference between VO2 at 6th min and VO2 at 3rd min during CWRE (DeltaVO2(6'-3')) was also determined. HIT induced significant improvement of most of the aerobic fitness parameters while most of these parameters returned to their pre-training level after detraining. Extra VO2 during IE was reduced after training (130 +/- 100 vs. -29 +/- 175 ml min(-1), P = 0.04) and was not altered after detraining compared to post-training. DeltaVO2(6'-3') during CWRE was unchanged by training and by detraining. We found a significant correlation (r2 = 0.575, P = 0.02) between extra VO2 and DeltaVO2(6'-3') before training. These results show that an alteration of extra VO2 can occur without any change in the VO2 slow component, suggesting a possible dissociation of the two phenomena. Moreover, the fact that extra VO2 did not change after detraining could indicate that this improvement may remain after the loss of other adaptations.

Exercise training in normobaric hypoxia in endurance runners. I. Improvement in aerobic performance capacity

This study investigates whether a 6-wk intermittent hypoxia training (IHT), designed to avoid reductions in training loads and intensities, improves the endurance performance capacity of competitive distance runners. Eighteen athletes were randomly assigned to train in normoxia [Nor group; n = 9; maximal oxygen uptake (VO2 max) = 61.5 +/- 1.1 ml x kg(-1) x min(-1)] or intermittently in hypoxia (Hyp group; n = 9; VO2 max = 64.2 +/- 1.2 ml x kg(-1) x min(-1)). Into their usual normoxic training schedule, athletes included two weekly high-intensity (second ventilatory threshold) and moderate-duration (24-40 min) training sessions, performed either in normoxia [inspired O2 fraction (FiO2) = 20.9%] or in normobaric hypoxia (FiO2) = 14.5%). Before and after training, all athletes realized 1) a normoxic and hypoxic incremental test to determine VO2 max and ventilatory thresholds (first and second ventilatory threshold), and 2) an all-out test at the pretraining minimal velocity eliciting VO2 max to determine their time to exhaustion (T(lim)) and the parameters of O2 uptake (VO2) kinetics. Only the Hyp group significantly improved VO2 max (+5% at both FiO2, P < 0.05), without changes in blood O2-carrying capacity. Moreover, T(lim) lengthened in the Hyp group only (+35%, P < 0.001), without significant modifications of VO2 kinetics. Despite similar training load, the Nor group displayed no such improvements, with unchanged VO2 max (+1%, nonsignificant), T(lim) (+10%, nonsignificant), and VO2 kinetics. In addition, T(lim) improvements in the Hyp group were not correlated with concomitant modifications of other parameters, including VO2 max or VO2 kinetics. The present IHT model, involving specific high-intensity and moderate-duration hypoxic sessions, may potentialize the metabolic stimuli of training in already trained athletes and elicit peripheral muscle adaptations, resulting in increased endurance performance capacity.

The relationship between the VO2 slow component, muscle metabolites and performance during very-heavy exhaustive exercise

This study examined the relationship between the V O(2) response, particularly the slow component (SC), muscle metabolite changes and performance during very-heavy exhaustive exercise. Sixteen active females performed a graded exercise test to determine V O(2peak) and the lactate threshold followed 48h later by a constant-load cycle test to exhaustion (ET) at 85% V O(2peak) intensity. Muscle biopsies and capillary blood samples were obtained before and after the ET to determine changes in muscle ATP, pH, lactate and phosphocreatine and also plasma pH and lactate. Breath-by-breath data from the ET were smoothed using 5-s averages and fit to a three-component exponential model. The mean time to exhaustion (t(exh)) during the ET was 16.8 (+/-6.4) min. Results showed no correlation between the SC and t(exh) or any muscle metabolite changes (p>0.05). Significant correlations (p<0.05) were evident between t(exh) and tau; tau(0) (r=-0.54), tau(1) (r=-0.65), change in (Delta) pH(b) (r=-0.60), Delta[La(-)](b) (r=-0.58) and [La(-)](b post) (r=-0.64). Significant correlations (p<0.05) were also evident between tau(1) and [La(-)](b post) (r=0.54). Furthermore, a negative value resulted when the accumulated oxygen deficit was calculated for the entire duration of the ET. Results showed no association between the amplitude of the SC and t(ext) or to changes in muscle/blood metabolites, suggesting that the SC is not a determinant of high-intensity exercise tolerance. Furthermore, it is possible that a reduced perturbation of anaerobic energy sources, as a result of a faster tau(1), may have contributed to a longer t(exh).

(.)VO(2) and EMG activity kinetics during moderate and severe constant work rate exercise in trained cyclists

The purpose of this study was to compare O(2) uptake ((.)VO(2)) and muscle electromyography activity kinetics during moderate and severe exercise to test the hypothesis of progressive recruitment of fast-twitch fibers in the explanation of the VO(2) slow component. After an incremental test to exhaustion, 7 trained cyclists (mean +/- SD, 61.4 +/- 4.2 ml x min(-1) x kg(- 1)) performed several square-wave transitions for 6 min at moderate and severe intensities on a bicycle ergometer. The (.)VO(2) response and the electrical activity (i.e., median power frequency, MDF) of the quadriceps vastus lateralis and vastus medialis of both lower limbs were measured continuously during exercise. After 2 to 3 min of exercise onset, MDF values increased similarly during moderate and severe exercise for almost all muscles whereas a (.)VO(2) slow component occurred during severe exercise. There was no relationship between the increase of MDF values and the magnitude of the (.)VO(2) slow component during the severe exercise. These results suggest that the origin of the slow component may not be due to the progressive recruitment of fast-twitch fibers.

Effects of high-intensity interval training on the VO2 response during severe exercise

This study examined the effect of high-intensity interval training on the VO2 response during severe, constant-load exercise. Prior to, and following training, 10 females (V O2 peak 37.4+/-6.0 mL kg-1 min-1) performed a graded exercise test to determine VO2 peak and lactate threshold (LT) and a 6 min cycle test (CT) at the pre-training VO2 peak intensity. Training involved high-intensity intervals (2 min work, 1 min rest) performed 3x week for 8 weeks. Breath-by-breath data from 0 to 6 min during the CT were smoothed using 5s averages and fit to a bi-exponential model starting from 20s. Training resulted in significant improvements in VO2 max (2.34+/-0.37-2.78+/-0.30 L min-1), power at VO2 max (170+/-26-204+/-25 W) and power at LT (113+/-17-136+/-20 W) (p<0.05). Following training, the VO2 response showed a significant increase in the amplitude of the primary phase (A1) (1396+/-103-1695+/-100 mL min-1; p<0.05) and end-exercise VO2 (VO2 EE), with no difference (p>0.05) in the time constants of either phase or the amplitude of the slow component (318+/-67-380+/-48 mL; p=0.15). In conjunction, accumulated oxygen deficit (AOD) (43.7+/-9.8-17.2+/-2.8 mL O2 eq kg-1) and anaerobic contribution to the CT (19.4+/-4.4-7.2+/-1.2%) were significantly reduced. In contrast to previous moderate-intensity research, a high-intensity interval training program increased A1 and VO2 EE for the same absolute exercise intensity, decreasing the AOD during a severe-intensity CT.