Effect of exercise modality on oxygen uptake kinetics during heavy exercise

A modified step-ramp-step protocol to prescribe constant-speed exercise in treadmill running

PURPOSE

This study investigated whether a running-adapted version of the cycling-based "step-ramp-step" (SRS) protocol would improve prediction of V ˙ O2 in treadmill exercise compared to the traditional prescriptive approach.

METHODS

Fourteen healthy individuals (6 females; 25 ± 6 years; 66.1 ± 12.7 kg) performed a treadmill-based SRS protocol including a ramp-incremental test to task failure followed by two constant-speed bouts within the moderate-(MODstep-below estimated lactate threshold; θLT), and heavy-intensity domains (HVYstep-between θLT and respiratory compensation point; RCP). Using the uncorrected V ˙ O2-to-speed relationship from the ramp exercise, three constant-speed bouts were performed at 40-50% between: baseline and θLT (CSEMOD); θLT and RCP (CSEHVY); and RCP and peak (CSESEV). For CSEMOD, CSEHVY, and CSESEV measured end-exercise V ˙ O2 was compared to predicted V ˙ O2 based on the: (i) "SRS-corrected" V ˙ O2-to-speed relationship (where MODstep and HVYstep were used to adjust the V ˙ O2 relative to speed); and (ii) linear "uncorrected" data.

RESULTS

Average treadmill speeds for CSEMOD and CSEHVY were 7.8 ± 0.8 and 11.0 ± 1.4 km·h-1, respectively, eliciting end-exercise V ˙ O2 of 1979 ± 390 and 2574 ± 540 mL·min-1. End-exercise V ˙ O2 values were not different compared to SRS-predicted V ˙ O2 at CSEMOD (mean difference: 5 ± 166 mL·min-1; p = 0.912) and CSEHVY (20 ± 128 mL·min-1; p = 0.568). The linear "uncorrected" estimates were not different for CSEMOD (- 91 ± 172 mL·min-1; p = 0.068) but lower for CSEHVY (- 195 ± 146 mL·min-1; p < 0.001). For CSESEV (running speed: 13.8 ± 1.7 km·h-1), the end-exercise V ˙ O2 was not different from peak V ˙ O2 achieved during the ramp (3027 ± 682 vs. 2979 ± 655 mL·min-1; p = 0.231).

CONCLUSION

In healthy individuals, the SRS protocol more accurately predicts speeds for a target V ˙ O2 compared to traditional approaches.

Prescription of High-intensity Aerobic Interval Training Based on Oxygen Uptake Kinetics

Endurance training results in diverse adaptations that lead to increased performance and health benefits. A commonly measured training response is the analysis of oxygen uptake kinetics, representing the demand of a determined load (speed/work) on the cardiovascular, respiratory, and metabolic systems, providing useful information for the prescription of constant load or interval-type aerobic exercise. There is evidence that during high-intensity aerobic exercise some interventions prescribe brief interval times (<1-min), which may lead to a dissociation between the load prescribed and the oxygen uptake demanded, potentially affecting training outcomes. Therefore, this review explored the time to achieve a close association between the speed/work prescribed and the oxygen uptake demanded after the onset of high-intensity aerobic exercise. The evidence assessed revealed that at least 80% of the oxygen uptake amplitude is reached when phase II of oxygen uptake kinetics is completed (1 to 2 minutes after the onset of exercise, depending on the training status). We propose that the minimum work-time during high-intensity aerobic interval training sessions should be at least 1 minute for athletes and 2 minutes for non-athletes. This suggestion could be used by coaches, physical trainers, clinicians and sports or health scientists for the prescription of high-intensity aerobic interval training.

Disparate Mechanisms of Fatigability in Response to Prolonged Running versus Cycling of Matched Intensity and Duration

INTRODUCTION

Running and cycling represent two of the most common forms of endurance exercise. However, a direct comparison of the neuromuscular consequences of these two modalities after prolonged exercise has never been made. The aim of this study was to compare the alterations in neuromuscular function induced by matched-intensity and duration cycling and running exercise.

METHODS

During separate visits, 17 endurance-trained male participants performed 3 h of cycling and running at 105% of the gas exchange threshold. Neuromuscular assessments were taken are preexercise, midexercise, and postexercise, including knee extensor maximal voluntary contractions (MVC), voluntary activation (VA), high- and low-frequency doublets (Db100 and Db10, respectively), potentiated twitches (Qtw,pot), motor evoked potentials (MEP), and thoracic motor evoked potentials (TMEP).

RESULTS

After exercise, MVC was similarly reduced by ~25% after both running and cycling. However, reductions in VA were greater after running (-16% ± 10%) than cycling (-10% ± 5%; P < 0.05). Similarly, reductions in TMEP were greater after running (-78% ± 24%) than cycling (-15% ± 60%; P = 0.01). In contrast, reductions in Db100 (running vs cycling, -6% ± 21% vs -13% ± 6%) and Db10:100 (running vs cycling, -6% ± 16% vs -19% ± 13%) were greater for cycling than running (P ≤ 0.04).

CONCLUSIONS

Despite similar decrements in the knee extensor MVC after running and cycling, the mechanisms responsible for force loss differed. Running-based endurance exercise is associated with greater impairments in nervous system function, particularly at the spinal level, whereas cycling-based exercise elicits greater impairments in contractile function. Differences in the mechanical and metabolic demands imposed on the quadriceps could explain the disparate mechanisms of neuromuscular impairment after these two exercise modalities.

Exercise tolerance during flat over-ground intermittent running: modelling the expenditure and reconstitution kinetics of work done above critical power

Purpose

We compared a new locomotor-specific model to track the expenditure and reconstitution of work done above critical power (W´) and balance of W´ (W´_BAL) by modelling flat over-ground power during exhaustive intermittent running.

Method

Nine male participants completed a ramp test, 3-min all-out test and the 30–15 intermittent fitness test (30–15 IFT), and performed a severe-intensity constant work-rate trial (S_CWR) at the maximum oxygen uptake velocity (vV̇O_2max). Four intermittent trials followed: 60-s at vV̇O_2max + 50% Δ₁ (Δ₁ = vV̇O_2max − critical velocity [V_Crit]) interspersed by 30-s in light (S_L; 40% vV̇O_2max), moderate (S_M; 90% gas-exchange threshold velocity [V_GET]), heavy (S_H; V_GET + 50% Δ₂ [Δ₂ = V_Crit − V_GET]), or severe (S_S; vV̇O_2max − 50% Δ₁) domains. Data from Global Positioning Systems were derived to model over-ground power. The difference between critical and recovery power (D_CP), time constant for reconstitution of W´ (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau_{{W^{\prime}}}$$\end{document}τW′), time to limit of tolerance (T_LIM), and W´_BAL from the integral (W´_BALint), differential (W´_BALdiff), and locomotor-specific (OG-W´_BAL) methods were compared.

Results

The relationship between \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau_{{W^{\prime}}}$$\end{document}τW′ and D_CP was exponential (r² = 0.52). The \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau_{{W^{{\prime}}}}$$\end{document}τW′ for S_L, S_M, and S_H trials were 119 ± 32-s, 190 ± 45-s, and 336 ± 77-s, respectively. Actual T_LIM in the 30–15 IFT (968 ± 117-s) compared closely to T_LIM predicted by OG-W´_BAL (929 ± 94-s, P > 0.100) and W´_BALdiff (938 ± 84-s, P > 0.100) but not to W´_BALint (848 ± 91-s, P = 0.001).

Conclusion

The OG-W´_BAL accurately tracked W´ kinetics during intermittent running to exhaustion on flat surfaces.

Oxygen Uptake Kinetics in Youth: Characteristics, Interpretation, and Application

Pulmonary oxygen uptake ( V˙O2 ) kinetics, which describes the aerobic response to near instantaneous changes in metabolic demand, provides a valuable insight into the control and coordination of oxidative phosphorylation during exercise. Despite their applicability to the highly sporadic habitual physical activity and exercise patterns of children, relatively little is known regarding the influence of internal and external stimuli on the dynamic V˙O2 response. Although insufficient evidence is available during moderate-intensity exercise, an age-related slowing of the phase 2 time constant (τ) and augmentation of the V˙O2 slow component appears to manifest during heavy-intensity exercise, which may be related to changes in the muscle phosphate controllers of oxidative phosphorylation, muscle oxygen delivery and utilization, and/or muscle fiber type recruitment patterns. Similar to findings in adults, aerobic training is associated with a faster phase 2 τ and smaller V˙O2 slow component in youth, independent of age or maturity, indicative of an enhanced oxidative metabolism. However, a lack of longitudinal or intervention-based training studies limits our ability to attribute these changes to training per se. Further, methodologically rigorous studies are required to fully resolve the interaction(s) between age, sex, biological maturity, and external stimuli, such as exercise training and exercise intensity and the dynamic V˙O2 response at the onset and offset of exercise.

Cardiorespiratory Response to Different Exercise Tests in Interstitial Lung Disease

INTRODUCTION

The 6-min stepper test (6MST) has been used as an alternative to the 6-min walk test (6MWT) to assess exercise tolerance in patients with interstitial lung disease (ILD). Recent data suggest that the tests may involve different energy pathways and cardiorespiratory responses. We thus aimed to compare the cardiorespiratory responses of ILD patients during the 6MWT and the 6MST.

METHODS

Thirty-one patients with ILD were randomized to perform both tests in the order 6MST → 6MWT (n = 16) or 6MWT → 6MST (n = 15). Gas exchange, HR, and pulse O2 saturation (SpO2) were measured continuously, and dyspnoea, leg discomfort, and blood lactate concentration were assessed before and immediately after each test.

RESULTS

Oxygen uptake (V˙O2) was lower (P = 0.002) and respiratory equivalent ratio for O2 (V˙E/V˙O2) and RER were higher (both P < 0.001) during the 6MST compared with the 6MWT. The 6MST was also associated with higher blood lactate concentrations (6MST, 4.16 ± 1.95 mmol·L; 6MWT, 2.84 ± 1.17 mmol·L; P = 0.01), higher leg discomfort scores (6MST 5 ± 3 points, 6MWT 3 ± 2 points; P < 0.001), and smaller decreases in SpO2 (6MST -5% ± 5%, 6MWT -9% ± 6%; P < 0.001).

CONCLUSIONS

ILD patients exhibited greater ventilatory responses and lower arterial O2 desaturation during the 6MST compared with the 6MWT. The higher lactate concentrations and perceived muscle fatigue observed during the 6MST may indicate the presence of intertest differences in active muscle metabolism that could contribute to the distinct cardiorespiratory responses.

Importance of Assessing Cardiorespiratory Fitness in Clinical Practice: A Case for Fitness as a Clinical Vital Sign: A Scientific Statement From the American Heart Association

Mounting evidence has firmly established that low levels of cardiorespiratory fitness (CRF) are associated with a high risk of cardiovascular disease, all-cause mortality, and mortality rates attributable to various cancers. A growing body of epidemiological and clinical evidence demonstrates not only that CRF is a potentially stronger predictor of mortality than established risk factors such as smoking, hypertension, high cholesterol, and type 2 diabetes mellitus, but that the addition of CRF to traditional risk factors significantly improves the reclassification of risk for adverse outcomes. The purpose of this statement is to review current knowledge related to the association between CRF and health outcomes, increase awareness of the added value of CRF to improve risk prediction, and suggest future directions in research. Although the statement is not intended to be a comprehensive review, critical references that address important advances in the field are highlighted. The underlying premise of this statement is that the addition of CRF for risk classification presents health professionals with unique opportunities to improve patient management and to encourage lifestyle-based strategies designed to reduce cardiovascular risk. These opportunities must be realized to optimize the prevention and treatment of cardiovascular disease and hence meet the American Heart Association's 2020 goals.

Postexercise heart rate variability following treadmill and cycle exercise: a comparison study

The purpose of this study was to compare postexercise heart rate variability (HRV) immediately following acute bouts of treadmill (T) and cycle (C) exercise at 65% of mode-specific maximal oxygen consumption reserve (65% VO₂ R). Fourteen apparently healthy men participated in this study. On two separate and randomized days, each participant performed 30 min of exercise at 65% VO₂ R on T and C. Supine HRV was evaluated as normalized and log-transformed (ln) high-frequency (HF) and low-frequency (LF) spectral power, as well as the LF:HF ratio in 5-min segments immediately before (PRE) and at 10-15 min (POST1) and 25-30 min (POST2) following each exercise bout. There were no significant differences in the HRV values at PRE between the modalities. Following each exercise bout, lnHF was significantly lower at POST2 following C compared to T. In addition, lnLF and LF:HF were significantly higher at POST1 and POST2 following C compared to T. All HRV metrics returned towards baseline 30 min following T but remained significantly different than PRE values after C. These results suggest that following exercise at 65% of mode-specific VO₂ R, C is associated with a greater delay of postexercise HRV recovery than T in apparently healthy men.

A fast-start pacing strategy speeds pulmonary oxygen uptake kinetics and improves supramaximal running performance

The focus of the present study was to investigate the effects of a fast-start pacing strategy on running performance and pulmonary oxygen uptake () kinetics at the upper boundary of the severe-intensity domain. Eleven active male participants (28±10 years, 70±5 kg, 176±6 cm, 57±4 mL/kg/min) visited the laboratory for a series of tests that were performed until exhaustion: 1) an incremental test; 2) three laboratory test sessions performed at 95, 100 and 110% of the maximal aerobic speed; 3) two to four constant speed tests for the determination of the highest constant speed (HS) that still allowed achieving maximal oxygen uptake; and 4) an exercise based on the HS using a higher initial speed followed by a subsequent decrease. To predict equalized performance values for the constant pace, the relationship between time and distance/speed through log-log modelling was used. When a fast-start was utilized, subjects were able to cover a greater distance in a performance of similar duration in comparison with a constant-pace performance (constant pace: 670 m±22%; fast-start: 683 m±22%; P = 0.029); subjects also demonstrated a higher exercise tolerance at a similar average speed when compared with constant-pace performance (constant pace: 114 s±30%; fast-start: 125 s±26%; P = 0.037). Moreover, the mean response time was reduced after a fast start (constant pace: 22.2 s±28%; fast-start: 19.3 s±29%; P = 0.025). In conclusion, middle-distance running performances with a duration of 2–3 min are improved and response time is faster when a fast-start is adopted.

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.

Maximal accumulated oxygen deficit in running and cycling

The purpose of this study was to compare values of maximal accumulated oxygen deficit (MAOD; a measure of anaerobic capacity) in running and cycling. Twenty-seven women and 25 men performed exhaustive treadmill and cycle ergometer tests of ∼3 min, ∼5 min, and ∼7 min duration. Oxygen demands were estimated assuming a linear relationship between demand and intensity and also using upwardly curvilinear relationships. When oxygen demand was estimated using speed (with exponent 1.05), values for MAOD for the three running tests were virtually identical; the mean of the three values was 78 ± 7 mL·kg⁻¹. Use of an oxygen demand that was estimated using work rate (with exponent 1.00) generated the most similar values for MAOD from the three cycling tests (mean of 59 ± 6 mL·kg⁻¹). Consistent with the higher (p < 0.05) MAOD in running, peak post-exercise blood lactate concentrations were also higher (p < 0.05) in running (13.9 ± 2.2 mmol·L⁻¹) than in cycling (12.6 ± 2.4 mmol·L⁻¹). The results suggest that the relationship between oxygen demand and running speed is upwardly curvilinear for the speeds used to measure MAOD; the relationship between demand and cycle ergometer work rate is linear; MAOD is greater in running than in cycling.

Dietary nitrate supplementation reduces the O2cost of walking and running: a placebo-controlled study

Dietary supplementation with beetroot juice (BR) has been shown to reduce resting blood pressure and the O2cost of submaximal exercise and to increase tolerance to high-intensity cycling. We tested the hypothesis that the physiological effects of BR were consequent to its high NO3−content per se, and not the presence of other potentially bioactive compounds. We investigated changes in blood pressure, mitochondrial oxidative capacity (Qmax), and physiological responses to walking and moderate- and severe-intensity running following dietary supplementation with BR and NO3−-depleted BR [placebo (PL)]. After control (nonsupplemented) tests, nine healthy, physically active male subjects were assigned in a randomized, double-blind, crossover design to receive BR (0.5 l/day, containing ∼6.2 mmol of NO3−) and PL (0.5 l/day, containing ∼0.003 mmol of NO3−) for 6 days. Subjects completed treadmill exercise tests on days 4 and 5 and knee-extension exercise tests for estimation of Qmax(using31P-magnetic resonance spectroscopy) on day 6 of the supplementation periods. Relative to PL, BR elevated plasma NO2−concentration (183 ± 119 vs. 373 ± 211 nM, P < 0.05) and reduced systolic blood pressure (129 ± 9 vs. 124 ± 10 mmHg, P < 0.01). Qmaxwas not different between PL and BR (0.93 ± 0.05 and 1.05 ± 0.22 mM/s, respectively). The O2cost of walking (0.87 ± 0.12 and 0.70 ± 0.10 l/min in PL and BR, respectively, P < 0.01), moderate-intensity running (2.26 ± 0.27 and 2.10 ± 0.28 l/min in PL and BR, respectively, P < 0.01), and severe-intensity running (end-exercise O2uptake = 3.77 ± 0.57 and 3.50 ± 0.62 l/min in PL and BL, respectively, P < 0.01) was reduced by BR, and time to exhaustion during severe-intensity running was increased by 15% (7.6 ± 1.5 and 8.7 ± 1.8 min in PL and BR, respectively, P < 0.01). In contrast, relative to control, PL supplementation did not alter plasma NO2−concentration, blood pressure, or the physiological responses to exercise. These results indicate that the positive effects of 6 days of BR supplementation on the physiological responses to exercise can be ascribed to the high NO3−content per se.

Effect of prior exercise on pulmonary O2 uptake and estimated muscle capillary blood flow kinetics during moderate-intensity field running in men

The effect of prior exercise on pulmonary O2 uptake (VO2p) and estimated muscle capillary blood flow (Qm) kinetics during moderate-intensity, field-based running was examined in 14 young adult men, presenting with either moderately fast (16 s<tauVO2p<30 s; MFK) or very fast VO2p kinetics (tauVO2p<16 s; VFK) (i.e., primary time constant, tauVO2p). On four occasions, participants completed a square-wave protocol involving two bouts of running at 90-95% of estimated lactate threshold (Mod1 and Mod2), separated by 2 min of repeated supramaximal sprinting. VO2p was measured breath by breath, heart rate (HR) beat to beat, and vastus lateralis oxygenation {deoxy-hemoglobin/myoglobin concentration (deoxy-[Hb+Mb])} using near-infrared spectroscopy. Mean response time of Qm (Qm MRT) was estimated by rearranging the Fick equation, using VO2p and deoxy-[Hb+Mb] as proxies of muscle O2 uptake (VO2) and arteriovenous difference, respectively. HR, blood lactate concentration, total hemoglobin, and Qm were elevated before Mod2 compared with Mod1 (all P<0.05). tauVO2p was shorter in VFK compared with MFK during Mod1 (13.1+/-1.8 vs. 21.0+/-2.5 s, P<0.01), but not in Mod2 (12.9+/-1.5 vs. 13.7+/-3.8 s, P=1.0). Qm MRT was shorter in VFK compared with MFK in Mod1 (8.8+/-1.9 vs. 17.0+/-3.4 s, P<0.01), but not in Mod2 (10.1+/-1.8 vs. 10.5+/-3.5 s, P=1.0). During Mod2, HR kinetics were slowed, whereas mean deoxy-[Hb+Mb] response time was unchanged. The difference in tauVO2p between Mod1 and Mod2 was related to Qm MRT measured at Mod1 (r=0.71, P<0.01). Present results suggest that local O2 delivery (i.e., Qm) may be a factor contributing to the VO2 kinetic during the onset of moderate-intensity, field-based running exercise, at least in subjects exhibiting moderately fast VO2 kinetics.

'Priming' exercise and O2 uptake kinetics during treadmill running

We tested the hypothesis that priming exercise would speed V(O2) kinetics during treadmill running. Eight subjects completed a square-wave protocol, involving two bouts of treadmill running at 70% of the difference between the running speeds at lactate threshold (LT) and V(O2) max, separated by 6-min of walking at 4 km h(-1), on two occasions. Oxygen uptake was measured breath-by-breath and subsequently modelled using non-linear regression techniques. Heart rate and blood lactate concentration were significantly elevated prior to the second exercise bout compared to the first. However, V(O2) kinetics was not significantly different between the first and second exercise bouts (mean+/-S.D., phase II time constant, Bout 1: 16+/-3s vs. Bout 2: 16+/-4s; V(O2) slow component amplitude, Bout 1: 0.24+/-0.10 L min(-1)vs. Bout 2: 0.20+/-0.12 L min(-1); mean response time, Bout 1: 34+/-4s vs. Bout 2: 34+/-6s; P>0.05 for all comparisons). These results indicate that, contrary to previous findings with other exercise modalities, priming exercise does not alter V(O2) kinetics during high-intensity treadmill running, at least in physically active young subjects. We speculate that the relatively fast V(O2) kinetics and the relatively small V(O2) slow component in the control ('un-primed') condition negated any enhancement of V(O2) kinetics by priming exercise in this exercise modality.

Neuromuscular and circulatory adaptation during combined arm and leg exercise with different maximal work loads

Cardiopulmonary kinetics and electromyographic activity (EMG) during exhausting exercise were measured in 8 males performing three maximal combined arm+leg exercises (cA+L). These exercises were performed at different rates of work (mean+/-SD; 373+/-48, 429+/-55 and 521+/-102 W) leading to different average exercise work times in all tests and subjects. VO2 reached a plateau versus work rate in every maximal cA+L exercise (range 6 min 33 s to 3 min 13 s). The three different exercise protocols gave a maximal oxygen consumption (VO2MAX) of 4.67+/-0.57, 4.58+/-0.52 and 4.66+/-0.53 l min(-1) (P=0.081), and a maximal heart rate (HRmax) of 190+/-6, 189+/-4 and 189+/-6 beats min(-1) (P=0.673), respectively. Root mean square EMG (EMGRMS) of the vastus lateralis and the triceps brachii muscles increased with increasing rate of work and time in all three cA+L protocols. The study demonstrates that despite different maximal rates of work, leading to different times to exhaustion, the circulatory adaptation to maximal exercise was almost identical in all three protocols that led to a VO2 plateau. The EMG(RMS) data showed increased muscle recruitment with increasing work rate, even though the HRmax and VO2MAX was the same in all three cA+L protocols. In conclusion, these findings do not support the theory of the existence of a central governor (CG) that regulates circulation and neuronal output of skeletal muscles during maximal exercise.

Comparação entre diferentes métodos de análise do componente lento do consumo de oxigênio: uma abordagem no domínio muito intenso de exercício

O objetivo do presente estudo foi comparar, em domínio muito intenso de exercício, diferentes técnicas utilizadas para medir a amplitude do componente lento (CL) da cinética do consumo de oxigênio. Dez ciclistas treinados, do gênero masculino [média ± DP (idade: 25 ± 3,6 anos, massa corporal: 67,2 ± 4,5kg, altura: 174,8 ± 6,5cm e VO2max: 62,4 ± 3,1ml.kg¹.min¹)], realizaram duas idênticas transições de carga constante (intensidade de 75%delta: 75% da diferença entre o VO2 no limiar de lactato e o VO2max) em dias diferentes. O CL foi calculado a partir de diferentes métodos: (1) modelo biexponencial [VO2(t) = VO2base + A1 (1 e-(t-TA1/t1)) + A2 (1 e(tTA2/t2))], (2) intervalos predeterminados (o deltaVO26-2: diferença do VO2 entre o segundo e o sexto minuto de exercício e o deltaVO263: diferença do VO2 entre o terceiro e o sexto minuto de exercício) e (3) diferença entre o VO2 obtido no final do exercício e o valor obtido a partir de um ajuste monoexponencial do "componente primário" (tempo predeterminado de 120s) (CL6"CP"). Todos os métodos foram comparados entre si. Os resultados demonstraram significante subestimação do CL obtido pelo método de intervalos predeterminados (deltaVO26-2: 432 ± 126ml.min¹ e deltaVO263: 279 ± 88ml.min¹) quando comparado com o modelo biexponencial (676 ± 136ml.min¹) e ao CL6"CP" [(719 ± 265ml.min¹ (p < 0,05)]. Não houve diferenças significativas entre as outras comparações. Os resultados sugerem que a utilização de tempos predeterminados pode subestimar o CL quando comparado com o modelo biexponencial e com o CL6"CP".

Relationship between maximal oxygen uptake and oxygen uptake attained during treadmill middle-distance running

Traditionally, it has been assumed that during middle-distance running oxygen uptake (VO2) reaches its maximal value (VO2max) providing the event is of a sufficient duration; however, this assumption is largely based on observations in individuals with a relatively low VO2max. The aim of this study was to determine whether VO2max is related to the VO2 attained (i.e. VO2peak) during middle-distance running on a treadmill. Fifteen well-trained male runners (age 23.3 +/- 3.8 years, height 1.80 +/- 0.10 m, body mass 76.9 +/- 10.6 kg) volunteered to participate in the study. The participants undertook two 800-m trials to examine the reproducibility of the VO2 response. These two trials, together with a progressive test to determine VO2max, were completed in a randomized order. Oxygen uptake was determined throughout each test using 15-s Douglas bag collections. Following the application of a 30-s rolling average, the highest VO2 during the progressive test (i.e. VO2max) was compared with the highest VO2 during the 800-m trials (i.e. VO2peak) to examine the relationship between VO2max and the VO2 attained in the 800-m trials. For the 15 runners, VO2max was 58.9 +/- 7.1 ml x kg(-1) x min(-1). Two groups were formed using a median split based on VO2max. For the high and low VO2max groups, VO2max was 65.7 +/- 3.0 and 52.4 +/- 1.8 ml x kg(-1) x min(-1) respectively. The limits of agreement (95%) for test-retest reproducibility for the VO2 attained during the 800-m trials were +/- 3.5 ml x kg(-1) x min(-1) for a VO2peak of 50.6 ml x kg(-1) x min(-1) (the mean VO2peak for the low VO2max group) and +/- 2.3 ml x kg(-1) x min(-1) for a VO2peak of 59.0 ml x kg(-1) x min(-1) (the mean VO2peak for the high VO2max group), with a bias in VO2peak between the 800-m runs (i.e. the mean difference) of 1.2 ml x kg(-1) x min(-1). The VO2peak for the 800-m runs was 54.8 +/- 4.9 ml x kg(-1) x min(-1) for all 15 runners. For the high and low VO2max groups, VO2peak was 59.0 +/- 3.3 ml x kg(-1) x min(-1) (i.e. 90% VO2max) and 50.6 +/- 2.0 ml x kg(-1) x min(-1) (i.e. 97% VO2max) respectively. The negative relationship (-0.77) between VO2max and % VO2max attained for all 15 runners was significant (P = 0.001). These results demonstrate that (i) reproducibility is good and (ii) that VO2max is related to the %VO2max achieved, with participants with a higher VO2max achieving a lower %VO2max in an 800-m trial on a treadmill.

Effect of pedaling technique on muscle activity and cycling efficiency

The purpose of this study was to examine the acute effect of talocrural joint position on muscle activity and gross mechanical efficiency (GE). Eleven trained cyclists participated in three randomized 6-min cycling bouts at approximately 80% of maximal aerobic capacity on an electromagnetically braked cycle ergometer while oxygen consumption and muscle activity (EMG) were monitored during the subject's self-selected pedaling technique (control) and while using a dorsi- and plantarflexed pedaling technique. The mean differences in range of motion of the dorsi- and plantarflexed technique from the control position were 7.1 +/- 4.4 and 6.9 +/- 5.4 degrees , respectively. Gastrocnemius EMG activity was higher with the dorsiflexion technique than when using the self-selected control position (33.2 +/- 13.0 and 24.2 +/- 8.4 microV s, respectively; P < 0.05). Moreover, GE was 2.6% lower while riding with the dorsiflexion technique than the control position (19.0 +/- 1.2 and 19.5 +/- 1.3%, respectively; P < 0.05). The data suggested that introducing more dorsiflexion into the pedal stroke of a trained cyclist increases muscle activity of the gastrocnemius lateralis and decreased GE when compared to the self-selected pedal stroke.

Componente lento do VO2 em crianças durante exercício pesado de corrida: análise com base em diferentes modelos matemáticos

O objetivo deste estudo foi verificar e quantificar a magnitude do componente lento do consumo de oxigênio (CL) em crianças submetidas a exercícios de corrida em esteira rolante, com cargas constantes de intensidade acima do limiar de lactato (75%D), utilizando para isso dois modelos de análise: a) modelo matemático com três termos exponenciais; e b) modelo deltaVO2 6-3min. Participaram do estudo oito crianças do sexo masculino (11,92 ± 0,63 anos; 44,06 ± 13,01kg; 146,63 ± 7,25cm; e níveis de maturação sexual 1 e 2), aparentemente saudáveis, não treinadas, que realizaram em diferentes dias: 1) teste incremental na esteira rolante para a determinação do consumo de oxigênio de pico (VO2pico) e do limiar de lactato (LL); e 2) dois testes de carga constante em esteira rolante durante seis minutos na intensidade de 75%delta [75%delta = LL + 0,75 x (VO2pico - LL)]. Para determinação do CL utilizaram-se: a) modelo matemático de três termos (Exp3); e b) a diferença no VO2 entre o sexto e o terceiro minuto de exercício (deltaVO2 6-3min). O CL foi expresso em valores absolutos (ml/min) e também como a contribuição percentual do CL para o aumento do VO2 no final do exercício (%CL). O CL determinado pelo modelo Exp3 (129,69 ± 75,71ml/min e 8,4 ± 2,92%) foi significantemente maior do que o obtido pelo modelo deltaVO2 6-3min (68,69 ± 102,54ml/min e 3,6 ± 7,34%). Portanto, os valores de CL obtidos em crianças durante o exercício de corrida realizado no domínio pesado (75%delta) são dependentes do modelo de análise (Exp3 x deltaVO2 6-3min).

Effects of dominant somatotype on aerobic capacity trainability

PURPOSE

This study examined the association between dominant somatotype and the effect on aerobic capacity variables of individualised aerobic interval training.

METHODS

Forty one white North African subjects (age 21.4+/-1.3 years; Vo2max = 52.8+/-5.7 ml kg(-1) min(-1)) performed three exercise tests 1 week apart (i) an incremental test on a cycle ergometer to determine Vo2max and Vo2 at the second ventilatory threshold (VT2); (ii) a VAM-EVAL track test to determine maximal aerobic speed (vVo2max); and (iii) an exhaustive constant velocity test to determine time limit performed at 100% vVo2max (tlim100). Subjects were divided into four somatometric groups: endomorphs-mesomorphs (Endo-meso; n = 9), mesomorphs (Meso; n = 11), mesomorphs-ectomorphs (Meso-ecto; n = 12), and ectomorphs (Ecto; n = 9). Subjects followed a 12 week training program (two sessions/week). Each endurance training session consisted of the maximal number of successive fractions for each subject. Each fraction consisted of one period of exercise at 100% of vVo2max and one of active recovery at 60% of vVo2max. The duration of each period was equal to half the individual tlim100 duration (153.6+/-39.7 s). After the training program, all subjects were re-evaluated for comparison with pre-test results.

RESULTS

Pre- and post-training data were grouped by dominant somatotype. Two way ANOVA revealed significant somatotype-aerobic training interaction effects (p<0.001) for improvements in vVo2max, Vo2max expressed classically and according to allometric scaling, and Vo2 at VT2. There were significant differences among groups post-training: the Meso-ecto and the Meso groups showed the greatest improvements in aerobic capacity.

CONCLUSION

The significant somatotype-aerobic training interaction suggests different trainability with intermittent and individualised aerobic training according to somatotype.

Cadence selection affects metabolic responses during cycling and subsequent running time to fatigue

OBJECTIVES

To investigate the effect of cadence selection during the final minutes of cycling on metabolic responses, stride pattern, and subsequent running time to fatigue.

METHODS

Eight triathletes performed, in a laboratory setting, two incremental tests (running and cycling) to determine peak oxygen uptake (VO2PEAK) and the lactate threshold (LT), and three cycle-run combinations. During the cycle-run sessions, subjects completed a 30 minute cycling bout (90% of LT) at (a) the freely chosen cadence (FCC, 94 (5) rpm), (b) the FCC during the first 20 minutes and FCC-20% during the last 10 minutes (FCC-20%, 74 (3) rpm), or (c) the FCC during the first 20 minutes and FCC+20% during the last 10 minutes (FCC+20%, 109 (5) rpm). After each cycling bout, running time to fatigue (Tmax) was determined at 85% of maximal velocity.

RESULTS

A significant increase in Tmax was found after FCC-20% (894 (199) seconds) compared with FCC and FCC+20% (651 (212) and 624 (214) seconds respectively). VO2, ventilation, heart rate, and blood lactate concentrations were significantly reduced after 30 minutes of cycling at FCC-20% compared with FCC+20%. A significant increase in VO2 was reported between the 3rd and 10th minute of all Tmax sessions, without any significant differences between sessions. Stride pattern and metabolic variables were not significantly different between Tmax sessions.

CONCLUSIONS

The increase in Tmax after FCC-20% may be associated with the lower metabolic load during the final minutes of cycling compared with the other sessions. However, the lack of significant differences in metabolic responses and stride pattern between the run sessions suggests that other mechanisms, such as changes in muscular activity, probably contribute to the effects of cadence variation on Tmax

Pulmonary O2 uptake on-kinetics in rowing and cycle ergometer exercise

The purpose of this study was to characterise, for the first time, the pulmonary O2 uptake (V(O2)) on-kinetic responses to step transitions to moderate and heavy intensity rowing ergometer exercise, and to compare the responses to those observed during upright cycle ergometer exercise. We hypothesised that the recruitment of a greater muscle mass in rowing ergometer exercise (Row) might limit muscle perfusion and result in slower Phase II V(O2) kinetics compared to cycle exercise (Cyc). Eight healthy males (aged 28+/-5 years) performed a series of step transitions to moderate (90% of the mode-specific gas exchange threshold, GET) and heavy (50% of the difference between the mode-specific GET and V(O2) max) work rates, for both Row and Cyc exercise. Pulmonary V(O2) was measured breath-by-breath and the V(O2) on-kinetics were described using standard non-linear regression techniques. With the exception of delta V(O2)delta WR which was approximately 12% greater for Row, the V(O2) kinetic responses were similar between the exercise modes. There was no significant difference in the time constant describing the Phase II V(O2) kinetics between the exercise modes for either moderate (rowing: 25.9+/-6.8 s versus cycling: 25.7+/-8.6 s) or heavy (rowing: 26.5+/-3.0 s versus cycling: 27.8+/-5.1s) exercise. Furthermore, there was no significant difference in the amplitude of the V(O2) slow component between the exercise modes (rowing: 0.34+/-0.13 L min(-1) versus cycling: 0.35+/-0.12 L min(-1)). These data suggest that muscle V(O2) increases towards the anticipated steady-state requirement at essentially the same rate following a step increase in ATP turnover in the myocytes, irrespective of the mode of exercise, at least in subjects with no particular sport specialism. The recruitment of a greater muscle mass in rowing compared to cycling apparently did not compromise muscle perfusion sufficiently to result either in slower Phase II V(O2) kinetics or a greater V(O2) slow component amplitude during heavy exercise.

Adaptation of pulmonary oxygen consumption slow component following 6 weeks of exercise training above and below the lactate threshold in untrained men

STUDY OBJECTIVES

To examine the effects of 6 weeks of exercise training above or below the lactate threshold (LT) on the slow component (SC) of pulmonary oxygen consumption (.VO(2)).

DESIGN

Randomized controlled trial.

SETTING

University human performance laboratory.

PARTICIPANTS

Apparently healthy, untrained men (n = 18).

INTERVENTIONS

Subjects were randomized to one of three groups: high-intensity exercise training (HI) [above the LT], moderate-intensity exercise training (MOD) [below the LT], or no exercise training (CON). Exercise groups performed cycle ergometry 4 d/wk for 6 weeks. Total work throughout training was constant between groups.

MEASUREMENTS AND RESULTS

Maximal cycle ergometry was performed at baseline and after training to assess power output at the LT (WLT), .VO(2) at the LT (.VO(2)LT), and peak .VO(2) (.VO(2)PK). High-intensity, constant-load cycling was performed at baseline and weeks 1, 2, 4, and 6 to assess SC adaptations. WLT, .VO(2)LT, and .VO(2)PK increased after 6 weeks in both exercise groups compared to the CON group (p < 0.05), although there were no differences between the training groups. SC of .VO(2) decreased 44% in the HI group following 1 week of exercise training vs MOD (20%, p < 0.05) and CON (12%, p < 0.01) groups. The SC attenuation was more prominent at all time points in the HI group compared to the MOD group. Total SC attenuation over the 6-week training period did not differ between the HI (71%) and MOD (57%) groups.

CONCLUSIONS

Training at HI or MOD produced similar improvements in the LT, .VO(2), and power output at peak exertion when total work output was held constant. Attenuation of the SC with training above and below the LT were similar, although above-LT training promoted faster SC adaptations.

Oxygen uptake kinetics during severe intensity running and cycling

The purpose of this study was to investigate the effect of exercise mode on the characteristics of the oxygen uptake (VO(2)) ()response to exercise within the severe intensity domain. Twelve participants each performed a treadmill running test and a cycle ergometer test to fatigue at intensities selected to elicit a mode-specific VO(2)max and to cause fatigue in ~5 min. The tests were at 234 (30) m.min(-1) and 251 (59) W, and times to fatigue were 297 (15) s and 298 (14) s, respectively. The overall rapidity of the VO(2)response was influenced by exercise mode [VO(2)max was achieved after 115 (20) s in running versus 207 (36) s in cycling; p<0.01]. VO(2) responses were fit to a three-phase exponential model. The time constant of the primary phase was faster in treadmill tests than in cycle ergometer tests [14 (6) s versus 25 (4) s; p<0.01], and the amplitude of the primary phase was greater in running than in cycling when it was expressed in absolute terms [2327 (393) ml.min(-1) versus 2036 (301) ml.min(-1); p=0.02] but not when it was expressed as a percentage of the total increase in VO(2) [86 (6)% versus 82 (6)%; p=0.09]. When quantified as the difference between the end-exercise VO(2) and the VO(2) at 2 min, the amplitude of the slow component was ~40% smaller in running [177 (92) ml.min(-1) versus 299 (153) ml min(-1); p=0.03]. It is concluded that exercise modality affects the characteristics of the VO(2) response at equivalent intensities in the severe domain.

Effect of prior exercise on VO(2) slow component is not related to muscle temperature

INTRODUCTION

It has been widely reported that the VO(2) slow component is reduced in the second of two bouts of heavy exercise. It has also been shown that an increase in muscle temperature (Tm) produced by wearing hot-water-perfused pants causes a reduction in the VO(2) slow component. Therefore, the aim of this study was to investigate whether the effect of prior heavy exercise on the VO(2) slow component of subsequent heavy exercise is related to the warming-up of the exercising limbs.

METHODS

Six male subjects completed an exercise protocol consisting of two constant-load exercise bouts (EX-1 and EX-2) at 90% VO(2peak), separated by 6 min of rest. The Tm of the m. vastus lateralis was measured with an indwelling thermistor. Seven days later, the subjects completed a second exercise protocol consisting of a passive warming-up of the upper legs until the same Tm was reached as after EX-1, followed by a constant-load work bout (EX-3) identical to EX-1 and EX-2.

RESULTS

Tm reached comparable levels at the start of EX-2 and EX-3 (37.3 +/- 0.6 degrees C and 37.2 +/- 0.3 degrees C, respectively). The VO(2) slow component (measured as deltaVO(2)(6-2 min)) was reduced by 57% after prior heavy exercise ( < 0.05), whereas no significant reduction was observed after prior passive warming-up.

CONCLUSIONS

The results of this study indicate that the reduction in VO(2) slow component observed after prior heavy exercise cannot be explained by an increase in muscle temperature of the upper legs.

Is the elevated slope relating ventilation to carbon dioxide production in chronic heart failure a consequence of slow metabolic gas kinetics?

OBJECTIVE

Patients with heart failure have slow metabolic gas exchange kinetics, which may contribute to the elevated slope of the relationship between ventilation and carbon dioxide production (Ve/Vco(2) slope).

SETTING

A tertiary referral centre for cardiology.

SUBJECTS

Eleven patients with stable chronic heart failure and 11 age-matched controls.

DESIGN

Each subject underwent maximal bicycle-based peak exercise testing with metabolic gas exchange analysis and three further repeated tests at 15%, 25% and 50% of the load achieved at peak exercise. The ventilation and carbon dioxide production from each of these steady-state tests was used to re-calculate the Ve/Vco(2) slope and compared with the Ve/Vco(2) slope derived from the maximal test.

RESULTS

Peak oxygen consumption [mean (S.D.)] was lower in heart failure patients [18.2 (4.0) vs. 31.2 (6.3) ml/kg per min; P<0.001] than in controls. The Ve/Vco(2) slope was steeper in patients than controls [32.7 (8.3) vs. 27.1 (1.6); P<0.05]. There was no difference between the Ve/Vco(2) slope reconstructed from the three steady state tests and resting data and that gained from the maximal test [35.3 (7.8) vs. 25.9 (3.2); P=0.43].

CONCLUSIONS

The elevated slope of the relationship between ventilation and carbon dioxide production is not a consequence of the short stages of a standard incremental exercise test combined with delayed metabolic gas kinetics in heart failure patients.

Influence of cycling cadence on subsequent running performance in triathletes

PURPOSE

The purpose of this study was to investigate the influence of different cycling cadences on metabolic and kinematic parameters during subsequent running.

METHODS

Eight triathletes performed two incremental tests (running and cycling) to determine maximal oxygen uptake (VO2max) and ventilatory threshold (VT) values, a cycling test to assess the energetically optimal cadence (EOC), three cycle-run succession sessions (C-R, 30-min cycle + 15-min run), and one 45-min isolated run (IR). EOC, C-R, and IR sessions were realized at an intensity corresponding to VT + 5%. During the cycling bouts of C-R sessions, subjects had to maintain one of the three pedaling cadences corresponding to the EOC (72.5 +/- 4.6 rpm), the freely chosen cadence (FCC; 81.2 +/- 7.2 rpm), and the theoretical mechanical optimal cadence (MOC, 90 rpm; Neptune and Hull, 1999).

RESULTS

Oxygen uptake (VO2) increased during the 30-min cycling only at MOC (+12.0%) and FCC (+10.4%). During the running periods of C-R sessions, VO2, minute ventilation, and stride-rate values were significantly higher than during the IR session (respectively, +11.7%, +15.7%, and +7.2%). Furthermore, a significant effect of cycling cadence was found on VO2 variability during the 15-min subsequent run only for MOC (+4.1%) and FCC (+3.6%).

CONCLUSION

The highest cycling cadences (MOC, FCC) contribute to an increase in energy cost during cycling and the appearance of a VO2 slow component during subsequent running, whereas cycling at EOC leads to a stability in energy cost of locomotion with exercise duration. Several hypotheses are proposed to explain these results such as changes in fiber recruitment or hemodynamic modifications during prolonged exercise.

Comparison of oxygen uptake kinetics during concentric and eccentric cycle exercise

O2 uptake (VO2) kinetics and electromyographic (EMG) activity from the vastus medialis, rectus femoris, biceps femoris, and medial gastrocnemius muscles were studied during constant-load concentric and eccentric cycling. Six healthy men performed transitions from baseline to high-intensity eccentric (HE) exercise and to high-intensity (HC), moderate-intensity (MC), and low-intensity (LC) concentric exercise. For HE and HC exercise, absolute work rate was equivalent. For HE and LC exercise, VO2 was equivalent. VO2 data were fit by a two- or three-component exponential model. Surface EMG was recorded during the last 12 s of each minute of exercise to obtain integrated EMG and mean power frequency. Only in the HC exercise did VO2 increase progressively with evidence of a slow component (phase 3), and only in HC exercise was there evidence of a coincident increase with time in integrated EMG of the vastus medialis and rectus femoris muscles (P < 0.05) with no change in mean power frequency. The phase 2 time constant was slower in HC [24.0 +/- 1.7 (SE) s] than in HE (14.7 +/- 2.8 s) and LC (16.7 +/- 2.2 s) exercise, while it was not different from MC exercise (20.6 +/- 2.1 s). These results show that the rate of increase in VO2 at the onset of exercise was not different between HE and LC exercise, where the metabolic demand was similar, but both had significantly faster kinetics for VO2 than HC exercise. The VO2 slow component might be related to increased muscle activation, which is a function of metabolic demand and not absolute work rate.

Oxygen uptake kinetics during treadmill running in boys and men

The purpose of this study was to compare the kinetics of the oxygen uptake (VO(2)) response of boys to men during treadmill running using a three-phase exponential modeling procedure. Eight boys (11-12 yr) and eight men (21-36 yr) completed an incremental treadmill test to determine lactate threshold (LT) and maximum VO(2). Subsequently, the subjects exercised for 6 min at two different running speeds corresponding to 80% of VO(2) at LT (moderate exercise) and 50% of the difference between VO(2) at LT and maximum VO(2) (heavy exercise). For moderate exercise, the time constant for the primary response was not significantly different between boys [10.2 +/- 1.0 (SE) s] and men (14.7 +/- 2.8 s). The gain of the primary response was significantly greater in boys than men (239.1 +/- 7.5 vs. 167.7 +/- 5.4 ml. kg(-1). km(-1); P < 0.05). For heavy exercise, the VO(2) on-kinetics were significantly faster in boys than men (primary response time constant = 14.9 +/- 1.1 vs. 19.0 +/- 1.6 s; P < 0.05), and the primary gain was significantly greater in boys than men (209.8 +/- 4.3 vs. 167.2 +/- 4.6 ml. kg(-1). km(-1); P < 0.05). The amplitude of the VO(2) slow component was significantly smaller in boys than men (19 +/- 19 vs. 289 +/- 40 ml/min; P < 0.05). The VO(2) responses at the onset of moderate and heavy treadmill exercise are different between boys and men, with a tendency for boys to have faster on-kinetics and a greater initial increase in VO(2) for a given increase in running speed.

Effect of endurance training on oxygen uptake kinetics during treadmill running

The purpose of this study was to examine the effect of endurance training on oxygen uptake (VO(2)) kinetics during moderate [below the lactate threshold (LT)] and heavy (above LT) treadmill running. Twenty-three healthy physical education students undertook 6 wk of endurance training that involved continuous and interval running training 3-5 days per week for 20-30 min per session. Before and after the training program, the subjects performed an incremental treadmill test to exhaustion for determination of the LT and the VO(2 max) and a series of 6-min square-wave transitions from rest to running speeds calculated to require 80% of the LT and 50% of the difference between LT and maximal VO(2). The training program caused small (3-4%) but significant increases in LT and maximal VO(2) (P<0.05). The VO(2) kinetics for moderate exercise were not significantly affected by training. For heavy exercise, the time constant and amplitude of the fast component were not significantly affected by training, but the amplitude of the VO(2) slow component was significantly reduced from 321+/-32 to 217+/-23 ml/min (P<0.05). The reduction in the slow component was not significantly correlated to the reduction in blood lactate concentration (r = 0. 39). Although the reduction in the slow component was significantly related to the reduction in minute ventilation (r = 0.46; P<0.05), it was calculated that only 9-14% of the slow component could be attributed to the change in minute ventilation. We conclude that the VO(2) slow component during treadmill running can be attenuated with a short-term program of endurance running training.