ArticleLiterature Review

Effects of Prior Exercise on Metabolic and Gas Exchange Responses to Exercise

February 2003
Sports Medicine 33(13):949-71

DOI:10.2165/00007256-200333130-00002

Source
PubMed

Authors:

Andrew M Jones

University of Exeter

Mark Burnley

University of Kent

'Warm-up' activity is almost universally performed by athletes prior to their participation in training or competition. However, relatively little is known about the optimal intensity and duration for such exercise, or about the potential mechanisms primed by warm-up that might enhance performance. Recent studies demonstrate that vigorous warm-up exercise that normally results in an elevated blood and presumably muscle lactate concentration has the potential to increase the aerobic energy turnover in subsequent high-intensity exercise. The reduced oxygen deficit is associated with a reduction in both the depletion of the intramuscular phosphocreatine stores and the rate at which lactic acid is produced. Furthermore, the oxygen uptake 'slow component' that develops during high-intensity, ostensibly submaximal, exercise is attenuated. These factors would be hypothesised to predispose to increased exercise tolerance. Interestingly, the elevation of muscle temperature by prior exercise does not appear to be implicated in the altered metabolic and gas exchange responses observed during subsequent exercise. The physiological mechanism(s) that limit the rate and the extent to which muscle oxygen uptake increases following the onset of exercise, and which are apparently altered by the performance of prior heavy exercise, are debated. However, these mechanisms could include oxygen availability, enzyme activity and/or availability of metabolic substrate, and motor unit recruitment patterns. Irrespective of the nature of the control mechanisms that are influenced, 'priming' exercise has the potential to significantly enhance exercise tolerance and athletic performance. The optimal combination of the intensity, duration and mode of 'warm-up' exercise, and the recovery period allowed before the criterion exercise challenge, remain to be determined.

Muscle oxygen availability in response to exercise: influence of intensity and duration

Thesis

Full-text available

Nov 2016

Fabian Stöcker

Interval training evidentially triggers aerobic adaptions like improved fatty acid and carbohydrate oxidation rates. Increased local blood supply is supposed to be one important mechanism that underlies these effects. Two important determinants of interval training are intensity and duration of work intervals. However, knowledge is scarce on the detailed effect of exercise intensity (Study 1) and exercise duration (Study 2) on the other hand on post-exercise blood supply and oxygen availability. In order to study those issues, the effects of six different, interval training associated exercise intensities and durations on post-exercise musclular oxygen availability and relative changes in hemoglobin concentration have been examined. For both (1) and (2), relative changes in oxygenated and deoxygenated hemoglobin and total hemoglobin (ΔO2Hb, ΔHHb, ΔTHb) were monitored with near-infrared spectroscopy of the vastus lateralis muscle and pulmonary oxygen uptake (VO2) was assessed. In Study 1, 17 male subjects performed an experimental protocol consisting of 180 s cycling bouts at six exercise intensities (40–90% peak oxygen uptake, VO2peak) in randomized order, separated by 5 min rests. In order to estimate local muscle blood supply and oxygen provision, ΔHHb/ΔVO2 ratio and estimated capillary blood flow (Qcap) were calculated during recovery using a bi-exponential model. In Study 2, 18 healthy male subjects performed an experimental protocol of five exercise bouts (30 s, 60 s, 90 s, 120 s and 240 s) at 80% VO2peak in randomized order, separated by 5 min rests. To examine the influence of submaximal aerobic performance, subjects with gas exchange thresholds (GET) above 60% VO2peak (GET60+) were compared with subjects reaching GET below 60% VO2peak (GET60-). The results of Study 1 revealed a progressively increased ΔHHb/ΔVO2 ratio from 40% to 60% VO2peak. Above 60% VO2peak, it decreased progressively. Post-exercise ΔTHb and ΔO2Hb showed an overshoot in relation to pre-exercise values, which was equal following exercise at 40–60% VO2peak and rose significantly following higher exercise intensities. A plateau was reached following exercise at ≥80% VO2peak. Mean response time (MRT) of Qcap recovery increased significantly with increasing exercise intensity. Study 2 showed significantly increased post-exercise oxygen 2 availability and local blood supply following 90 s exercise duration without a further increase following longer exercise bouts. Considering submaximal aerobic performance, the GET60+ group reached maximum post-exercise oxygen availability also with shorter exercise (60 s) than the GET60- group (90 s). Based on the results, Study 1 shows a progressively increasing mismatch of local O2 delivery and utilization with increasing exercise intensity up to 60% VO2peak after 3 min exercise bouts as suggested by increasing end-exercise ΔHHb/ΔVO2 ratio. This suggests that microvascular perfusion does not adequately meet the increased metabolic demand up to this point. Interestingly, ΔHHb/ΔVO2 decreased above 60% VO2peak. Consequently, the matching of HHb and VO2 gets progressively impaired from 40% VO2peak to 60% VO2peak but is progressively improved at exercise intensities above 60% VO2peak up to 90% VO2peak. Postexercise oxygen availability also was improved above above 60% VO2peak, which was according to the transition from moderate to heavy intensity exercise (gas exchange threshold 59 ± 13% VO2peak). Consequently, beginning acidosis could have promoted local vasodilation. Study 2 results give evidence for a slower adjustment of local vasodilation in subjects with GET60- than GET60+. The key mechanism behind those effects presumably is an enhanced endothelium and flow-mediated vasodilation superimposing sympathetic vasoconstriction. These results suggest that cycling exercise is most efficient for enhancing local postexercise oxygen availability and blood supply when it is conducted (A) at least at 80% VO2peak and (B) with a minimum duration of 90 s for subjects wit GET60- while such with GET60+ have same effects following 60 s of exercise. Hence, interval training should be prescribed accordingly in order to promote aerobic effects.

Efeito da intensidade do exercício prévio na resposta fisiológica e na performance aeróbia de curta duração

Article

Full-text available

Dec 2014

DOI: http://dx.doi.org/10.5007/1980-0037.2015v17n1p112 Atletas de diferentes esportes têm usado frequentemente exercícios de aquecimento como forma de preparação para a sessão de treinamento ou a competição. Entre as razões que levam os técnicos a adotarem este procedimento estão o aumento no metabolismo e na performance, como também a prevenção de lesões musculoesqueléticas. Os efeitos do exercício prévio têm sido estudados para se analisar os fatores limitantes dos ajustes fisiológicos no início do exercício e seu efeito na performance do exercício subsequente. Assim, este artigo analisa estudos que investigaram os efeitos do exercício prévio nas respostas cardiorrespiratórias, metabólicas e na performance aeróbia de curta duração. Neste contexto, fatores como a intensidade e a duração do exercício prévio e o período de recuperação entre as sessões de exercício prévio e do exercício subsequente são discutidos. São apresentados também os possíveis mecanismos que poderiam explicar os efeitos do exercício prévio nas respostas fisiológicas e na performance. Os efeitos do exercício prévio na cinética do consumo de oxigênio (VO2) não parecem depender da intensidade do exercício prévio e do período de recuperação entre as sessões de exercício (i.e., prévio e subsequente). Porém, os efeitos na tolerância ao exercício parecem depender da interação entre a intensidade dos dois exercícios e do período de recuperação entre eles.

The effect of priming exercise on muscular fatigue after an all-out protocol

Conference Paper

Full-text available

Apr 2019

Introduction: Prior exercise, also known as “priming”, is suspected to affect the cardiovascular as well as muscular system (Jones, Koppo, & Burnley, 2003; Layec et al., 2009; Poole, Barstow, McDonough, & Jones, 2008). Many previous studies investigated metabolic processes that are affected by priming. But only a few studies referred prior exercise to muscular fatigue due to difficulties in inducing and measuring muscular fatigue with respect to the cardiovascular system (Maturana, Peyrard, Temesi, Millet, & Murias, 2017). It is supposed that improving local oxygen availability and utilization by prior exercise might improve the resistance against muscular fatigue (DiMenna et al., 2010). Therefore, the aim of this study was to assess (1) the effect of prior exercise on muscle oxygenation and (2) its influence on muscular fatigue after an all-out knee extension protocol. Methods: In a randomized cross-over design, 15 healthy males performed two times an all-out knee extension protocol in a motor driven, isokinetic dynamometer (D. & R. Ferstl GmbH, Hemau, Germany). After an unspecific warm-up, peak torque of maximum voluntary contraction (MVC), maximum voluntary activation level (MVA) and potentiated twitch torque were determined as baseline using the interpolated twitch technique (Gandevia, 2001). While 15 min passive rest were set in the control condition, priming exercise, clocked box jumps (30 cm high, 60 s, 80 bpm), and further fatigue measurements (MVC combined with ITT) were executed in the priming condition. To evolve the priming effects participants recovered for 15 min. After the resting phase, the participants performed 60 s of dynamic, all-out knee extension (concentric – eccentric) in both conditions. Immediately after the all-out exercise, the participants fulfilled the final interpolated twitch measurement to receive information about possible effects of priming exercise on muscular fatigue. Torque measurement, electromyography (Myon AG, Schwarzenberg Swiss) and near-infrared spectroscopy (NIRS, Artinis Medical Systems B.V., Elst, Netherlands) were used during the knee extension protocol to understand muscle activation and oxygenation. In this context, relative changes in deoxygenated hemoglobin (HHb) describe the dynamic balance between muscle oxygen consumption and availability (A. M. Jones, Koppo, & Burnley, 2003; Layec et al., 2009; Poole, Barstow, McDonough, & Jones, 2008). Muscle oxygenation response kinetics were fitted using a mono-exponential model regarding baseline, amplitude, time delay and time constant. Results: Central and peripheral fatigue after the knee extension exercise was not affected by priming box jumps and therefore no significant effect between the conditions was shown. While MVA level remained constant during the whole experiment, peak MVC as well as potentiated twitch torque decreased significantly between baseline, after priming and after all out exercise measurement (Fig. 2 A). Muscle oxygenation kinetics during the all-out exercise did not differ between both conditions nether in modeled output nor in average time course of HHb (Fig. 2 B). Angular momentum as well as muscle activation frequency declined in both conditions, while integrated EMG decreased only in non-primed control condition. Discussion: It was shown that priming exercise did not affect neither muscular fatigue nor muscle oxygenation. As one of the first studies, fatigue was induced and measured in a highly standardized but also isolated setup. Improvements in primed oxygen delivery, e.g. vasodilation and increased oxygen dissociation (A. M. Jones et al., 2003), might be compensated by high muscular pressure and thus occlusion of smaller vessels induced by all-out muscle activation. With limited oxidative glycolysis and maximum muscle activation a high amount of anaerobic metabolism, i.e. phosphocreatine (PCr) breakdown and anaerobic glycolysis, the all-out intensity itself inhibits priming effects on muscle fatigue (Broxterman, Layec, Hureau, Amann, & Richardson, 2017). Although PCr was not directly measured, almost the same MVC peak torque as well as potentiated twitch torques indicate that PCr breakdown might be identical in both conditions (Fig. 2). Consequently, prior exercise should aim to increase phosphocreatine storage and improve oxidative ATP synthesis (Layec et al., 2009). In this study, the combination of prior exercise, recovery duration and intensity of fatiguing task might depress possible effects, which must be adapted in further research. Intermittent, maximum intensity exercise or submaximal (e.g. 30% MVC), continuous exercise might allow possible priming effects in microvascular oxygen supply and thus increase aerobic metabolism to save high energy phosphates i.e. PCr. Furthermore, the onset of muscle deoxygenation response was difficult to model with the mono-exponential function that is used in many studies investigating onset kinetics. Because the time delay was determined by the fit and was not supposed to be a constant like in VO2 modelling, the primary response is overestimated in some participants.

Challenge bronchomotor tests in functional assessment of respiratory system in sportsmen

Article

Apr 2008

End-exercise ΔHHb/ΔVO2 and post-exercise local oxygen availability in relation to exercise intensity

Article

Nov 2015

Increased local blood supply is thought to be one of the mechanisms underlying oxidative adaptations to interval training regimes. The relationship of exercise intensity with local blood supply and oxygen availability has not been sufficiently evaluated yet. The aim of this study was to examine the effect of six different intensities (40-90% peak oxygen uptake, VO2peak ) on relative changes in oxygenated, deoxygenated and total haemoglobin (ΔO2 Hb, ΔHHb, ΔTHb) concentration after exercise as well as end-exercise ΔHHb/ΔVO2 as a marker for microvascular O2 distribution. Seventeen male subjects performed an experimental protocol consisting of 3 min cycling bouts at each exercise intensity in randomized order, separated by 5 min rests. ΔO2 Hb and ΔHHb were monitored with near-infrared spectroscopy of the vastus lateralis muscle, and VO2 was assessed. ΔHHb/ΔVO2 increased significantly from 40% to 60% VO2 peak and decreased from 60% to 90% VO2 peak. Post-exercise ΔTHb and ΔO2 Hb showed an overshoot in relation to pre-exercise values, which was equal after 40-60% VO2peak and rose significantly thereafter. A plateau was reached following exercise at ≥80% VO2peak . The results suggest that there is an increasing mismatch of local O2 delivery and utilization during exercise up to 60% VO2peak . This insufficient local O2 distribution is progressively improved above that intensity. Further, exercise intensities of ≥80% VO2peak induce highest local post-exercise O2 availability. These effects are likely due to improved microvascular perfusion by enhanced vasodilation, which could be mediated by higher lactate production and the accompanying acidosis.

Efeito do exercício prévio no ciclismo de curta duração

Article

Full-text available

Apr 2014

INTRODUÇÃO: O exercício prévio tem importantes implicações na preparação de atletas antes de competições. OBJETIVO: Analisar o efeito de um exercício prévio realizado no domínio pesado no pico de torque (PTORQUE) medido após exercício severo. MÉTODOS: Participaram deste estudo 14 homens ativos (idade: 26 ± 4 anos, VO2max: 44 ± 6 mLO2.min⁻¹.kg⁻¹⁾ que realizaram sete testes em dias diferentes: a) teste progressivo de rampa para determinação do VO2max e da potência pico; b) quatro testes de carga constante para determinação da potência crítica, capacidade de trabalho anaeróbio e potência correspondente ao tempo de exaustão de 3 min (PTLim3min) e; c) dois testes de carga constante de 2 min na PTLim3min seguidos por um sprint all out de 10 s, a fim de medir o PTORQUE. Este último protocolo foi realizado com (EP) e sem (CON) a realização de um exercício prévio pesado. RESULTADOS: O PTORQUE foi significantemente maior após o EP (101 ± 30 Nm) em relação à condição CON (95 ± 23 Nm). O tempo da resposta médio (TRM) do VO2 foi significantemente menor após o EP (24 ± 7 s) em relação à condição CON (32 ± 10 s). A amplitude primária do VO2 aumentou significantemente após o EP (2598 ± 421 mLO2.min⁻¹⁾ em relação à condição CON (2184 ± 246 mLO2.min⁻¹⁾. O déficit de O2 foi significantemente menor após o exercício prévio (980 ± 432 mLO2) em relação à condição CON (1273 ± 398 mLO2). Houve correlação significante entre a variação do déficit de O2 com a do PTORQUE (r = 0,53) e da variação do TRM com a do PTORQUE (r = 0,53). CONCLUSÃO: Pode-se concluir que o PTORQUE é maior após exercício aeróbio de curta duração precedido do EP. Deste modo, esta estratégia pode ser interessante como preparação para algumas competições esportivas.

Relationship of post-exercise muscle oxygenation and duration of cycling exercise

Article

Full-text available

Apr 2016

Background: Aerobic adaptations following interval training are supposed to be mediated by increased local blood supply. However, knowledge is scarce on the detailed relationship between exercise duration and local post-exercise blood supply and oxygen availability. This study aimed to examine the effect of five different exercise durations, ranging from 30 to 240 s, on post-exercise muscle oxygenation and relative changes in hemoglobin concentration. Methods: Healthy male subjects (N = 18) performed an experimental protocol of five exercise bouts (30, 60, 90, 120, and 240 s) at 80 % of peak oxygen uptake [Formula: see text] in a randomized order, separated by 5-min recovery periods. To examine the influence of aerobic fitness, we compared subjects with gas exchange thresholds (GET) above 60 % [Formula: see text] (GET60+) with subjects reaching GET below 60 % [Formula: see text] (GET60-). [Formula: see text] and relative changes in concentrations of oxygenated hemoglobin, deoxygenated hemoglobin, and total hemoglobin were continuously measured with near-infrared spectroscopy of the vastus lateralis muscle. Results: Post-exercise oxygen availability and local blood supply increased significantly until the 90-s exercise duration and reached a plateau thereafter. Considering aerobic fitness, the GET60+ group reached maximum post-exercise oxygen availability earlier (60 s) than the GET60- group (90 s). Conclusions: Our results suggest that (1) 90 s has evolved as the minimum interval duration to enhance local oxygen availability and blood supply following cycling exercise at 80 % [Formula: see text]; whereas (2) 60 s is sufficient to trigger the same effects in subjects with GET60 + .

The Effects of Warm-up Duration on Cycling Time Trial Performance in Trained Cyclists

Article

Full-text available

Jan 2017

The purpose of this study was to assess the effects of three different warm-up conditions on a 5K cycling time trial (TT). Sixteen trained cyclists completed the study. At the first testing session, participants completed a maximal graded exercise test to assess maximal oxygen consumption (VO2max) and a familiarization of the TT. At three subsequent visits, the participants completed the TT after no warm up, short warm-up of three minutes at 60% VO2max, or long warm up of ten minutes at 60% VO2max. The warm up was assigned in randomized order. VO2, heart rate (HR), lactate, power, and speed were assessed after the warm up, 1K, and completion of the 5K TT. There was no difference between type of warm up for time, power, cadence, speed, VO2, HR, or lactate levels at the end of the TT. There was no significant difference between type of warm up for time, VO2, or HR at the end of the 1K split. Warm up length was not impactful on 5K TT performance or during the first km of the TT in trained cyclists. These results conflict with previous evidence indicating that a warm up in endurance events primarily improved VO2 kinetics at the onset of the exercise.

Use of Loaded Conditioning Activities to Potentiate Middle- and Long-Distance Performance: A Narrative Review and Practical Applications

Article

Jan 2018

The warm-up is an integral component of a middle- and long-distance athlete's pre-performance routine. The use of a loaded conditioning activity (LCA), which elicits a post-activation potentiation (PAP) response to acutely enhance explosive power performance, is well-researched. A similar approach incorporated into the warm-up of a middle- or long-distance athlete potentially provides a novel strategy to augment performance. Mechanisms that underpin a PAP response, relating to acute adjustments within the neuromuscular system, should theoretically improve middle- and long-distance performance via improvements in sub-maximal force-generating ability. Attempts to enhance middle- and long-distance related outcomes using a LCA have been used in several recent studies. Results suggest benefits to performance may exist in well-trained middle- and long-distance athletes by including high-intensity resistance training (1-5 repetition maximum) or adding load to the sport skill itself during the latter part of warm-ups. Early stages of performance appear to benefit most, and it is likely that recovery (5-10 min) also plays an important role following a LCA. Future research should consider how priming activity, designed to enhance the V[Combining Dot Above]O2 kinetic response, and a LCA may interact to affect performance, and how different LCA's might benefit various modes and durations of middle- and long-distance exercise.

Successive contractile periods activate mitochondria at the onset of contractions in intact rat cardiac trabeculae

Article

Full-text available

Jan 2018

The rate of oxidative phosphorylation depends on the contractile activity of the heart. Cardiac mitochondrial oxidative phosphorylation is determined by free ADP concentration, mitochondrial Ca2+ accumulation, mitochondrial enzyme activities and Krebs cycle intermediates. The purpose of the present study was to examine the factors that limit oxidative phosphorylation upon rapid changes in contractile activity in cardiac muscle. We tested the hypotheses that prior contractile performance enhances the changes in NAD(P)H and FAD concentration upon an increase in contractile activity, and that this mitochondrial "priming" depends on pyruvate dehydrogenase activity. Intact rat cardiac trabeculae were electrically stimulated at 0.5 Hz for at least 30 min. Thereafter two equal bouts at elevated stimulation frequency of 1, 2 or 3 Hz were applied for 3 min with 3 min of 0.5 Hz stimulation in between. No discernible time delay was observed in the changes in NAD(P)H and FAD fluorescence upon rapid changes in contractile activity. The amplitudes of the rapid changes in fluorescence upon an increase in stimulation frequency (the on-transients) were smaller than upon a decrease in stimulation frequency (the off-transients). A first bout in glucose-containing superfusion solution resulted, during the second bout, in an increase in the amplitudes of the on-transients, but the off-transients remained the same. No such priming effect was observed after addition of 10 mM pyruvate. These results indicate that mitochondrial priming can be observed in cardiac muscle in situ and that pyruvate dehydrogenase activity is critically involved in the mitochondrial adaptation to increases in contractile performance.

Residual Fatigue Does Not Affect Critical Power And w´ Using A Single-visit Protocol: 852 May 27 3:15 PM - 3:25 PM

Article

Jul 2020
MED SCI SPORT EXER

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

Article

Full-text available

Sep 2021
SPORTS MED

A flattening of the oxygen uptake-work rate relationship at severe exercise indicates the achievement of maximum oxygen uptake [Formula: see text]. Unfortunately, a distinct plateau [Formula: see text] at [Formula: see text]is not found in all participants. The aim of this investigation was to critically review the influence of research methods and physiological factors on the [Formula: see text] incidence. It is shown that many studies used inappropriate definitions or methodical approaches to check for the occurrence of a [Formula: see text]. In contrast to the widespread assumptions it is unclear whether there is higher [Formula: see text] 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 [Formula: see text] have been achieved by all participants. As a result, there is little evidence for a higher [Formula: see text] incidence and a corresponding advantage for the diagnoses of [Formula: see text] when incremental tests are supplemented by supramaximal verification bouts. Preliminary evidence suggests that the occurrence of a [Formula: see text] in continuous incremental tests is determined by physiological factors like anaerobic capacity, [Formula: see text]-kinetics and accumulation of metabolites in the submaximal intensity domain. Subsequent studies should take more attention to the use of valid [Formula: see text] definitions, which require a cut-off at ~ 50% of the submaximal [Formula: see text] increase and rather large sampling intervals. Furthermore, if verification bouts are used to verify the achievement of [Formula: see text]/[Formula: see text], it should be ensured that they can be sustained for sufficient durations.

A 30-min Rest Protocol Does Not Affect W′, Critical Power, and Systemic Response

Article

Feb 2021
MED SCI SPORT EXER

Purpose: This study aimed to assess and compare the systemic response of oxygen uptake kinetics and muscle deoxygenation between a 30-min rest protocol and a multivisit protocol on the parameters of the power-duration relationship (i.e., critical power [CP] and W'). Methods: Nine endurance-trained triathletes reported to the laboratory on five occasions: a preliminary graded exercise test and a familiarization, a 30-min single-visit protocol (time trials of 10, 5, and 2 min in that order interspersed with 30 min rest), and a multivisit protocol (time trials of 10, 5, and 2 min in randomized order interspersed by >24 h rest). Heart rate (HR) was recorded continuously, respiratory gases were measured breath by breath, and deoxygenation was recorded at 10 Hz using near-infrared spectroscopy (NIRS) during all tests. Blood lactate (BLa-) concentration was measured before all time trials. Maximal HR (HRmax), oxygen uptake (V˙O2) during the first 2 min (V˙O2onset), mean response time, end-exercise V˙O2 (V˙O2peak), V˙O2 amplitude (amplV˙O2), O2 deficit, NIRS τ, amplitude (amplNIRS), and time delay were assessed. To compare the two protocols and to assess the differences in W' and CP, a paired sample t-test was used as well as a two-way ANOVA to assess the differences between trials and/or protocols, including trial-protocol interactions. Results: No significant differences, and trivial effect sizes, were found for W' and CP between protocols (P = 0.106-0.114, d < 0.01-0.08). Furthermore, no significant differences between protocols were found for all parameters, except for [BLa-]. Significant differences between trials were found for V˙O2ampl, V˙O2onset, NIRS τ, amplNIRS, [BLa-], and HRmax. Conclusion: Results suggest that W' and CP can be determined using the 30-min rest protocol without confounding effects of previous severe exercise compared with the multivisit protocol.

Optimisation of Warm-Up Protocols in Soccer

Article

Full-text available

James Zois

Blood-Flow Restricted Warm-Up Alters Muscle Hemodynamics and Oxygenation during Repeated Sprints in American Football Players

Article

Full-text available

May 2019

Team-sport athletes and coaches use varied strategies to enhance repeated-sprint ability (RSA). Aside from physical training, a well-conducted warm-up enhances RSA via increased oxidative metabolism. Strategies that impede blood flow could potentiate the effects of a warm-up due to their effects on the endothelial and metabolic functions. This study investigated whether performing a warm-up combined with blood-flow restriction (WFR) induces ergogenic changes in blood volume, muscle oxygenation, and RSA. In a pair-matched, single-blind, pre-post parallel group design, 15 American football players completed an RSA test (12 × 20 m, 20 s rest), preceded by WFR or a regular warm-up (SHAM). Pressure was applied on the athletes’ upper thighs for ≈15 min using elastic bands. Both legs were wrapped at a perceived pressure of 7 and 3 out of 10 in WFR and SHAM, respectively. Changes in gastrocnemius muscle oxygen saturation (SmO2) and total hemoglobin concentration ([THb]) were monitored with near-infrared spectroscopy. Cohen’s effect sizes (ES) were used to estimate the impact of WFR. WFR did not clearly alter best sprint time (ES −0.25), average speed (ES 0.25), total time (ES −0.12), and percent decrement score (ES 0.39). While WFR did not meaningfully alter average SmO2 and [THb], the intervention clearly increased the maximum [THb] and the minimum and maximum SmO2 during some of the 12 sprint/recovery periods (ES 0.34–1.43). Results indicate that WFR positively alters skeletal muscle hemodynamics during an RSA test. These physiological changes did not improve short-term RSA, but could be beneficial to players during longer activities such as games.

Warm-Up Strategies for Sport and Exercise: Mechanisms and Applications

Article

Full-text available

Nov 2015
SPORTS MED

It is widely accepted that warming-up prior to exercise is vital for the attainment of optimum performance. Both passive and active warm-up can evoke temperature, metabolic, neural and psychology-related effects, including increased anaerobic metabolism, elevated oxygen uptake kinetics and post-activation potentiation. Passive warm-up can increase body temperature without depleting energy substrate stores, as occurs during the physical activity associated with active warm-up. While the use of passive warm-up alone is not commonplace, the idea of utilizing passive warming techniques to maintain elevated core and muscle temperature throughout the transition phase (the period between completion of the warm-up and the start of the event) is gaining in popularity. Active warm-up induces greater metabolic changes, leading to increased preparedness for a subsequent exercise task. Until recently, only modest scientific evidence was available supporting the effectiveness of pre-competition warm-ups, with early studies often containing relatively few participants and focusing mostly on physiological rather than performance-related changes. External issues faced by athletes pre-competition, including access to equipment and the length of the transition/marshalling phase, have also frequently been overlooked. Consequently, warm-up strategies have continued to develop largely on a trial-and-error basis, utilizing coach and athlete experiences rather than scientific evidence. However, over the past decade or so, new research has emerged, providing greater insight into how and why warm-up influences subsequent performance. This review identifies potential physiological mechanisms underpinning warm-ups and how they can affect subsequent exercise performance, and provides recommendations for warm-up strategy design for specific individual and team sports.

Towards an understanding of the mechanistic bases of V̇O2 kinetics

Article

Full-text available

Jan 2005

A detailed comparison of oxygen uptake kinetics at a range of exercise intensities

Research

Apr 2015

Cain C. T. Clark

Masters by Research thesis looking at a detailed comparison of oxygen uptake kinetics at a range of exercise intensities

The Oxygen Uptake Response to Incremental Ramp Exercise Methodogical and Physiological Issues

Article

Jan 2012

An incremental ramp exercise is a protocol that is frequently used in the domain of exercise testing to get an insight into the exercise tolerance of both healthy active populations (including athletes) and patients, due to the specific characteristics of the protocol. The continuous and linear increase in work rate is not only less strenuous for populations with a very low exercise capacity but it requires the aerobic metabolism to adapt to the continuously changing conditions. Therefore, this protocol can provide important information on the adaptive capacity of individuals to exercise in non-steady-state conditions. The ramp exercise has also been used in the past two decades to get an insight into the underlying mechanisms of the oxygen uptake ((V) over dotO(2)) response (and kinetics) to exercise. Against the expectations, it has been shown that the parameters that quantify the (V) over dotO(2) response to ramp exercise do not completely correspond to those obtained from constant work-rate transitions and incremental step exercise. For that reason, it could be concluded that the (V) over dotO(2) response is specific to ramp exercise, and thus is determined by other mechanisms than those which determine other protocols. Although the (V) over dotO(2) response to ramp exercise has a high level of reproducibility and a uniform pattern can be observed, especially for the (V) over dotO(2) response below the gas exchange threshold (GET) [above the GET, the (V) over dotO(2) response is less clear], some prudence is necessary when interpreting potential differences in the (V) over dotO(2) response between populations. Several methodological issues (e.g. baseline work rate, ramp slope) exert an important impact on the (V) over dotO(2) response to ramp exercise. The main purpose of this review is to provide an overview of the methodological and physiological factors that have an impact on the (V) over dotO(2) response to ramp exercise. It is of importance that exercise physiologists take these factors into consideration, not only prior to the conductance of the ramp exercise in a variety of subjects, but also when interpreting the obtained results.

Are the oxygen uptake and heart rate off-kinetics influenced by the intensity of prior exercise?

Article

May 2016
RESP PHYSIOL NEUROBI

The aim of this study was to investigate the effect of prior exercise on the heart rate (HR) and oxygen uptake (VO2) off-kinetics after a subsequent high-intensity running exercise. Thirteen male futsal players (age 22.8 ± 6.1 years) performed a series of high-intensity bouts without prior exercise (control), preceded by a prior same intensity continuous exercise (CE+CE) and a prior sprint exercise (SE+CE). The magnitude of excess post-exercise oxygen consumption (EPOCm − 4.25 ± 0.19 vs. 3.69 ± 0.20 L min−1 in CE+CE and 3.62 ± 0.18 L min−1 in control; p < 0.05) and the parasympathetic reactivation (HRR60s − 33 ± 3 vs. 37 ± 3 bpm in CE+CE and 42 ± 3 bpm in control; p < 0.05) in the SE+CE were higher and slower, compared with another two conditions. The EPOCτ (time to attain 63% of total response; 53 ± 2 s) and the heart rate time-course (HRτ − 86 ± 5 s) were significantly longer after the SE+CE condition than control transition (48 ± 2 s and 69 ± 5 s, respectively; p < 0.05). The SE+CE induce greater stress on the metabolic function, respiratory system and autonomic nervous system regulation during post-exercise recovery than CE, highlighting that the inclusion of sprint-based exercises can be an effective strategy to increase the total energy expenditure following an exercise session.

Re-Evaluation of Old Findings on Stroke Volume Responses to Exercise and Recovery by Nitrous-Oxide Rebreathin

Article

Full-text available

Oct 2016
J HUM KINET

It is important to verify the old findings of Cumming (1972) and Goldberg and Shephard (1980) who showed that stroke volume (SV) may be higher during recovery rather than during exercise, in order to organize the number of intervals throughout training sessions. The purpose of this study was to re-evaluate individual SV responses to various upright cycling exercises using the nitrous-oxide rebreathing method. Nine moderate to well-trained male athletes volunteered to take part in the study (maximal O2 uptake (VO2max): 60.2 ± 7 mL⋅min⁻¹⋅kg⁻¹). Workloads ranging from 40-100% of VO2max were applied to determine individual peak SV (SVpeak) response. Results showed that SV responses were higher during exercise compared to recovery in all exercise loads from 40-100% of VO2max. Mean SV responses to individual SVpeak loads were also higher during exercise compared to recovery (122.9 ± 2.5 versus 105.3 ± 5.93 mL). The highest SV responses to 10 min exercises of 40-70% of VO2max were obtained in the 5th or 7.5th min of each stage (p≤0.05). Meanwhile, during 5 min exercises between 80-100% of VO2max, peak SV responses were observed in the 3rd min of loading (p≤0.05). In conclusion, individual SVpeak levels encountered over wide exercise intensity ranges showed that SVpeak development may also be correlated to exercise intensity corresponding to individual SVpeak loads.

Five repeated maximal efforts of apneas increase the time to exhaustion in subsequent high-intensity exercise

Article

Jun 2021
RESP PHYSIOL NEUROBI

Ten subjects were tested on a cycle ergometer to exhaustion with intensity corresponding to 150 % of their peak power output (TF150) under three conditions [C: base line measurement; PRE: after five repeated breath hold maneuvers (BH); and POST: after 5BH, preceded by two weeks of BH training]. Respiratory and blood measurements were carried out. Upon cessation of 5BH, subjects compared to C condition started TF150 with reduced arterialized blood pH (C:7.428±0.023, PRE:7.419±0.016, POST:7.398±0.021) and elevated bicarbonate concentration (mmol/l), ventilation (l/min) and oxygen uptake (ml/min) (C:28.4±1.5, PRE:29.9±1.2, POST:30.0±1.8; C:10.4±2.5, PRE:13.3±3.3, POST:15.6±5.6; C:333.0±113.8, PRE:550.1±131.1, POST:585.1±192.8, respectively). After TF150, subjects had significantly reduced pH and elevated ventilation, and oxygen uptake in PRE and POST, in comparison to the C condition. TF150 (sec) significantly improved after 5BH without being further affected by BH training (C:44.8±8.1, PRE:49.2±4.8, POST:49.3±8.2). Priming breath holds prior to middle-distance racing may improve performance.

High-intensity cycling re-warm up within a very short time-frame increases the subsequent intermittent sprint performance

Article

Full-text available

Jan 2020
EUR J SPORT SCI

This study investigated the effect of high-intensity cycling re-warm up (RW) within a very short time-frame on the subsequent intermittent sprint performance. Twelve active males completed three trials in random order: control (CON); 3-min RW at 30% of maximal oxygen uptake (VO2max) (RW30); and 1-min RW at 90% of VO2max (RW90). During the experimental trials, participants performed 40 min of intermittent cycling exercise followed by 15 min of rest. During the rest period, participants completed CON, RW30, or RW90. After the rest period, participants performed the Cycling Intermittent-Sprint Protocol (CISP), which consisted of 10 seconds of rest, 5 seconds of maximal sprint, and 105 seconds of active recovery with the cycles repeated over 10 min. The mean work during sprint for the CISP was significantly higher in both RW trials than in the CON trial (mean ± standard deviation; CON: 3539 ± 698 J; RW30: 3724 ± 720 J; RW90: 3739 ± 736 J; p < 0.05). The mean electromyogram amplitude during the sprint for the CISP was higher in the RW30 trial than in the CON trial; however, there was no significant difference between the two trials (p = 0.06). The mean median frequency during sprint for the CISP was significantly higher in the RW90 trial than in the CON and RW30 trials (p < 0.05). Rectal temperature did not differ between trials. Oxygenated haemoglobin during the initial 30 s of the CISP was significantly higher in the RW90 trial than in the CON trial (p < 0.05). Compared with seated rest, RW, irrespective of whether it comprised 1 min at 90% of VO2max or 3 min at 30% of VO2max, increased the subsequent intermittent sprint performance.

Whole body active warm up and inspiratory muscle warm up do not improve running performance when carrying thoracic loads

Article

Full-text available

Mar 2017

Whole body active warm ups (AWU) and inspiratory muscle warm up (IMW) prior to exercise improves performance on some endurance exercise tasks. This study investigated the effects of AWU with and without IMW upon 2.4 km running time-trial performance while carrying a 25 kg backpack, a common task and backpack load in physically demanding occupations. Participants (n = 9) performed five 2.4 km running time-trials with a 25 kg thoracic load preceded in random order by 1) IMW comprising 2 x 30 inspiratory efforts against a pressure-threshold load of 40 % maximal inspiratory pressure (PImax), 2) 10 min unloaded running (AWU) at lactate turnpoint (10.33 ± 1.58 km·h-1), 3) placebo IMW (PLA) comprising five min breathing using a sham device, 4) AWU+IMW and 5) AWU+PLA. Pooled baseline PImax was similar between trials and increased by 7% and 6% following IMW and AWU+IMW (P<0.05). Relative to baseline, pooled PImax was reduced by 9% after the time-trial, which was not different between trials (P>0.05). Time-trial performance was not different between any trials. Whole body AWU and IMW performed alone or combination have no ergogenic effect upon high intensity, short duration performance when carrying a 25 kg load in a backpack.

Time Trials Versus Time-to-Exhaustion Tests: Effects on Critical Power, W', and Oxygen-Uptake Kinetics

Article

Full-text available

May 2017
Int J Sports Physiol Perform

Purpose: To investigate single-day time-to-exhaustion (TTE) and time trial (TT) based laboratory tests values of critical power (CP), Wprime (W') and respective oxygen kinetics responses. Methods: Twelve cyclists performed a maximal ramp test followed by three TTE and three TT efforts interspersed by a 60-min recovery between efforts. Oxygen uptake was measured during all trials. The mean response time (MRT) was calculated as a description of the overall V̇O2 kinetic response from the onset to 2 min of exercise. Results: TTE determined CP was 279 ± 52W and TT determined CP was 276 ± 50W (P = 0.237). Values of W' were 14.3 ± 3.4 kJ (TTE W') and 16.5± 4.2 kJ (TT W') (P = 0.028). Whilst a high level of agreement (-12 to 17 W) and a low prediction error of 2.7% was established for CP, for W' limits of agreements were markedly lower (-8 to 3.7 kJ) with a prediction error of 18.8%. The mean standard error for TTE CP values was significantly higher than that for TT CP values (2.4 ± 1.9% vs. 1.2 ± 0.7% W). The standard error for TTE W' and TT W' were 11.2 ± 8.1% and 5.6 ± 3.6%, respectively. The V̇O2 response was significantly faster during TT (~22 s) than TTE (~28 s). Conclusions: The time-trial protocol with a 60-min recovery period offers a valid, time-saving and less error containing alternative to conventional and more recent testing methods. Results however cannot be transferred to W'.

Faster V̇O2 kinetics after priming exercises of different duration but same fatigue

Article

Jul 2017
J SPORT SCI

This study compared the responses of two priming exercises of similar fatigue on the adjustment of the oxygen uptake time constant (τV̇O2) in cycling. Ten healthy young adults (25 ± 3 yr) performed: three step transitions from a 20-W baseline to the power output (PO) below the gas exchange threshold (MOD, MODPRE); a 3-min bout (P3MIN) at 90% of peak PO (POpeak), followed by MOD (MOD3MIN); and a 6-min bout (P6MIN) at 80% of POpeak, followed by MOD (MOD6MIN). The O2 supply-to-O2 demand ([HHb]/V̇O2) ratio was calculated for MODPRE, MOD3MIN, and MOD6MIN. Neuromuscular fatigue was measured isometrically pre- and post-priming exercise. Reductions in maximal voluntary contraction (−29 ± 6 vs −34 ± 7%) and high-frequency doublet amplitude (−48 ± 13 vs −43 ± 11%) were not significantly different between P3MIN vs P6MIN, suggesting similar fatigue. τV̇O2 for MOD3MIN and MOD6MIN were similar, being ~25% smaller than MODPRE. The [HHb]/V̇O2 ratio was significantly greater in MODPRE (1.13 ± 0.12) compared to MOD3MIN (1.02 ± 0.04) and MOD6MIN (1.02 ± 0.04). This study showed that priming exercise of shorter duration and higher intensity, was sufficient to accelerate V̇O2 kinetics similarly to that observed subsequent to P6MIN when the muscle fatigue was similar.

Running economy: Measurement, norms, and determining factors

Article

Full-text available

Dec 2015

Running economy (RE) is considered an important physiological measure for endurance athletes, especially distance runners. This review considers 1) how RE is defined and measured and 2) physiological and biomechanical factors that determine or influence RE. It is difficult to accurately ascertain what is good, average, and poor RE between athletes and studies due to variation in protocols, gas-analysis systems, and data averaging techniques. However, representative RE values for different caliber of male and female runners can be identified from existing literature with mostly clear delineations in oxygen uptake across a range of speeds in moderately and highly trained and elite runners. Despite being simple to measure and acceptably reliable, it is evident that RE is a complex, multifactorial concept that reflects the integrated composite of a variety of metabolic, cardiorespiratory, biomechanical and neuromuscular characteristics that are unique to the individual. Metabolic efficiency refers to the utilization of available energy to facilitate optimal performance, whereas cardiopulmonary efficiency refers to a reduced work output for the processes related to oxygen transport and utilization. Biomechanical and neuromuscular characteristics refer to the interaction between the neural and musculoskeletal systems and their ability to convert power output into translocation and therefore performance. Of the numerous metabolic, cardiopulmonary, biomechanical and neuromuscular characteristics contributing to RE, many of these are able to adapt through training or other interventions resulting in improved RE.

The Effect of Half-time Re-Warm up Duration on Intermittent Sprint Performance

Article

Full-text available

May 2018
J SPORT SCI MED

The purpose of the present study was to investigate the effect of different durations of half-time re-warm up (RW) on intermittent sprint performance. Using a randomized crossover design, 13 healthy men performed three trials, which consisted of two, 40-min intermittent exercises separated by a 15-min half-time. Half-time interventions were 15 min of seated rest (Control), 7 min of cycling at 70% of maximal heart rate (HRmax) (7 min RW), and 3 min of cycling at 70% of HRmax (3 min RW). The second 40-min intermittent exercise as an exercise performance test was the Cycling Intermittent-Sprint Protocol (CISP), which consisted of 10 s of rest, 5 s of maximal sprint, and 105 s of low-intensity exercise at 50% of VO2max, with the cycles repeated over the 40-min duration. The mean work during the maximal sprint in the initial 10 min of the CISP was higher in the both RW trials than in the control trial (control: 3638 ± 906 J, 7 min RW: 3808 ± 949 J, p < 0.05, 3 min RW: 3827 ± 960 J, p < 0.05). There were no significant differences among three trials for mean work at 10-20, 20-30, and 30-40 min of the CISP. In the initial 10 min of the CISP, the change in oxygenated hemoglobin concentration during the 105 s of exercise at 50% of VO2max, oxygen uptake, carbon dioxide production, and respiratory exchange ratio were higher in both RW trials than in the control trial (p < 0.05). The rating of perceived exertion after half-time interventions was higher in both RW trials than in the control trial (p < 0.05). In conclusion, the 3 min RW increased intermittent sprint performance after the half-time, compared with a traditional passive half-time practice, and was as effective in improving intermittent sprint performance as the 7 min RW.

Effects of high intensity continuous and intermittent training strategies used for endurance development on cardiovascular responses

Presentation

Full-text available

Jul 2018

Effects of a single dose of beetroot juice on cycling time trial performance at ventilatory thresholds intensity in male triathletes

Article

Full-text available

Dec 2018
Sports Nutr Rev J

Background: Beetroot juice (BJ) is classified as a high-level supplement for improving sports performance. There is some controversy over the benefits of BJ supplementation for endurance exercise performance, especially when referring to well-trained athletes. This study examines the effects of acute BJ supplementation on cardioventilatory responses, exercise economy/efficiency, slow component of oxygen uptake, time trial performance, blood lactate, energy consumption, and carbohydrate and fat oxidation. Methods: Twelve well-trained, male triathletes (aged 21–47 yr) were assigned in a randomized, double-blind, crossover design to receive 70 ml of BJ (6.5 mmol NO3−) or placebo (PL). Three hours after taking the supplement, participants completed an endurance test on a cycle ergometer at a constant work rate (W) corresponding to first ventilatory threshold (VT1) (30 min) and second ventilatory threshold (VT2) time trial (~ 15 min). Results: Maximal oxygen uptake was 54.78 ± 3.13 mL·min− 1·kg− 1, and gross efficiency was > 22% at each load intensity and experimental condition. No significant interaction effect (supplement*intensity) was observed on any of the cardioventilatory variables, efficiency/economy, VT2 time trial, energy expenditure, carbohydrate oxidation and fat oxidation (p > 0.05). Conclusion: Our findings do not support an improvement in the variables examined in response to acute BJ supplementation. Probably, higher doses are needed for improving time trial performance in male triathletes during a cycle ergometer test conducted at a load intensity equivalent to the first and second ventilatory threshold.

Les effets du préconditionnement métabolique sur l'oxygénation musculaire et sur la performance en patinage de vitesse longue piste

Thesis

Dec 2018

Philippe Richard

Influence of Warm-Up Prior to Incremental Exercise Test on Aerobic Performance in Physically Active Men

Article

Full-text available

Feb 2020

Introduction. The aim of the study was to verify the influence of warm-up before a ramp incremental exercise test with linearly increasing loads on the maximal values of physiological variables which determine performance. Material and methods. Thirteen healthy and physically active male students (age = 23.3 ± 1.5 years, body height = 179.1 ± 8.6 cm and body mass = 79.5 ± 9.1 kg) completed a cross-over comparison of two incremental exercise test interventions – an incremental exercise test with a 15-minute warm-up at an intensity of 60% of the maximal oxygen uptake obtained in the first incremental exercise test and the same test without warm-up. Results. The peak values of physiological variables were statistically significantly higher for the incremental exercise test with warm-up, the differences between tests being 2.66% for peak power output (p = 0.039, t = 2.312, ES = 0.24), 7.75% for peak oxygen uptake (p = 0.000, t = 5.225, ES = 0.56), 7.72% for peak minute ventilation (p = 0.005, t = 3.346, ES = 0.53) and 1.62% for peak heart rate (p = 0.019, t = 2.690, ES = 0.60). Conclusions. Warm-up before a ramp incremental exercise test resulted in higher values of maximal oxygen uptake, maximal minute ventilation, maximal heart rate and peak power output.

Reduction of V̇O2 slow component by priming exercise: novel mechanistic insights from time‐resolved near‐infrared spectroscopy

Article

Full-text available

Jun 2015

Novel time-resolved near-infrared spectroscopy (TR-NIRS), with adipose tissue thickness correction, was used to test the hypotheses that heavy priming exercise reduces the V̇O2 slow component (V̇O2SC) (1) by elevating microvascular [Hb] volume at multiple sites within the quadriceps femoris (2) rather than reducing the heterogeneity of muscle deoxygenation kinetics. Twelve subjects completed two 6-min bouts of heavy work rate exercise, separated by 6 min of unloaded cycling. Priming exercise induced faster overall V̇O2 kinetics consequent to a substantial reduction in the V̇O2SC (0.27 ± 0.12 vs. 0.11 ± 0.09 L·min(-1), P < 0.05) with an unchanged primary V̇O2 time constant. An increased baseline for the primed bout [total (Hb + Mb)] (197.5 ± 21.6 vs. 210.7 ± 22.5 μmol L(-1), P < 0.01), reflecting increased microvascular [Hb] volume, correlated significantly with the V̇O2SC reduction. At multiple sites within the quadriceps femoris, priming exercise reduced the baseline and slowed the increase in [deoxy (Hb + Mb)]. Changes in the intersite coefficient of variation in the time delay and time constant of [deoxy (Hb + Mb)] during the second bout were not correlated with the V̇O2SC reduction. These results support a mechanistic link between priming exercise-induced increase in muscle [Hb] volume and the reduced V̇O2SC that serves to speed overall V̇O2 kinetics. However, reduction in the heterogeneity of muscle deoxygenation kinetics does not appear to be an obligatory feature of the priming response. © 2015 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.

Oxygen uptake and blood flow kinetics following the onset of exercise in trained humans

Article

Full-text available

Azmy Faisal

Warming Up, Strength

Article

Full-text available

Jun 2013

Vincent Teo

Optimaal 'opwarmen' voor maximale prestaties

Article

Full-text available

Jan 2008

Florentina Johanna Hettinga

Een goede warming up is belangrijk voor het leveren van een goede sportprestatie. Hoewel de naam suggereert dat het er bij een warming up om gaat om warm te worden, is dat niet het enige wat een rol speelt bij het verbeteren van prestatie. Een goede warming up verhoogt ook de aanvoer van O2 en heeft daarmee een groot effect heeft op de VO2 respons, d.w.z. op het verloop van de zuurstof-opname tijdens een inspanning. Door de warming up goed te kiezen kan het aërobe systeem maximaal benut worden.

Determinants of Oxygen Uptake

Article

Nov 1997

For exercise modalities such as cycling which recruit a substantial muscle mass, muscle oxygen uptake (V̇O2) is the primary determinant of pulmonary V̇O2. Indeed, the kinetic complexities of pulmonary V̇O2 associated with exercise onset and the non-steady states of heavy (>lactate threshold) and severe [>asymptote of power-time relationship for high intensity exercise (Ẇ)] exercise reproduce with close temporal and quantitative fidelity those occurring across the exercising muscles. For moderate (<lactate threshold) exercise and also rapidly incremental work tests, pulmonary (and muscle) V̇O2 increases as a linear function of work rate (≈9 to 11 ml O2/W/min) in accordance with theoretical determinations of muscle efficiency (≈30%). In contrast, for constant load exercise performed in the heavy and severe domains, a slow component of the V̇O2 response is manifest and pulmonary and muscle V̇O2 increase as a function of time as well as work rate beyond the initial transient associated with exercise onset. In these instances, muscle efficiency is reduced as the V̇O2 cost per unit of work becomes elevated, and in the severe domain, this V̇O2 slow component drives V̇O2 to its maximum and fatigue ensues rapidly. At pulmonary maximum oxygen uptake (V̇O2max) during cycling, the maximal cardiac output places a low limiting ceiling on peak muscle blood flow, O2 delivery and thus muscle V̇O2. However, when the exercise is designed to recruit a smaller muscle mass (e.g. leg extensors, 2 to 3kg), mass-specific muscle blood flow and V̇O2 at maximal exercise are 2 to 3 times higher than during conventional cycling. Consequently, for any exercise which recruits more than ≈5 to 6kg of muscle at pulmonary V̇O2max there exists a mitochondrial or V̇O2 reserve capacity within the exercising muscles which cannot be accessed due to oxygen delivery limitations. The implications of these latter findings relate to the design of exercise tests. Specifically, if the purpose of exercise testing is to evaluate the oxidative capacity of a small muscle mass (<5 to 6kg), the testing procedure should be designed to restrict the exercise to those muscles so that a central (cardiac output, muscle O2 delivery) limitation is not invoked. It must be appreciated that exercise which recruits a greater muscle mass will not stress the maximum mass-specific muscle blood flow and V̇O2 but rather the integration of central (cardiorespiratory) and peripheral (muscle O2 diffusing capacity) limitations.

Multiple Sprint Work

Article

Sep 2005

Mark Glaister

The activity patterns of many sports (e.g. badminton, basketball, soccer and squash) are intermittent in nature, consisting of repeated bouts of brief (≤-second) maximal/near-maximal work interspersed with relatively short (≤60-second) moderate/low-intensity recovery periods. Although this is a general description of the complex activity patterns experienced in such events, it currently provides the best means of directly assessing the physiological response to this type of exercise. During a single short (5- to 6-second) sprint, adenosine triphosphate (ATP) is resynthesised predominantly from anaerobic sources (phosphocreatine [PCr] degradation and glycolysis), with a small (

Transport of Oxygen and Carbon Dioxide in Blood and Tissue Fluids

Chapter

Jun 2006

Muscle Cramping During a 161-km Ultramarathon: Comparison of Characteristics of Those With and Without Cramping

Article

Full-text available

Jun 2015

This work sought to identify characteristics differing between those with and without muscle cramping during a 161-km ultramarathon. In this observational study, race participants underwent body weight measurements before, during, and after the race; completed a post-race questionnaire about muscle cramping and “near” cramping (controllable, not reaching full-blown cramping), drinking strategies, and use of sodium supplementation during four race segments; and underwent a post-race blood draw for determination of serum sodium and blood creatine kinase (CK) concentrations. The post-race questionnaire was completed by 280 (74.5 %) of the 376 starters. A post-race blood sample was provided by 181 (61.1 %) of the 296 finishers, and 157 (53.0 %) of finishers completed the post-race survey and also provided a post-race blood sample. Among those who completed the survey, the prevalence of cramping and near cramping was 14.3 and 26.8 %, respectively, with greatest involvement being in the calf (54 %), quadriceps (44 %), and hamstring (33 %) muscles. Those with cramping or near cramping were more likely to have a prior history of muscle cramping during an ultramarathon (p < 0.0001) and had higher blood CK concentrations (p = 0.001) than those without cramping. Weight change during the race, use of sodium supplements, intake rate of sodium in supplements, and post-race serum sodium concentration did not differ between those with and without cramping. Muscle cramping is most common in those with a prior history of cramping and greater muscle damage during an ultramarathon, suggesting an association with relative muscular demand. Impaired fluid and sodium balance did not appear to be an etiology of muscle cramping during an ultramarathon.

Total parenteral nutrition

Article

Jan 2011

Oxygen and carbon dioxide transport

Article

Jan 2011

A review: Analyzing how VO 2 kinetics limit exercise performance

Article

Jun 2011

J. Harvey

This brief review analyzes the effect of VO 2 kinetics on exercise performance. It will focus on exercise above and below the lactate threshold (LT), and how VO 2 kinetics and other factors modify exercise performance in different physiological states. Below the LT, VO 2 is not found to be the limiting factor in exercise performance. Above LT, an increasing number of factors must be taken into consideration though VO 2 kinetics play a major role as VO 2 max is approached.

The affects of a warm-up and the recovery interval prior to exercise on anaerobic power and acid-base balance in man

Article

Full-text available

Dec 2007

The main objective of the paper was to evaluate the influence of warm up and the rest interval separating it from exercise on maximal anaerobic power and acid-base balance (ABB). The research material included 12 students of physical education with an average age, maximal oxygen uptake, body height and mass The students performed 3 exercise trials. During trial I a 30s Wingate test wits preceded by a 15 min warm-up performed on a ergocycle with the intensity set at 50% VO(2)max and the pedaling frequency equal to 60 rev./min. The rest interval between the end of warm-up and the onset of exercise equaled 5 min. During the second trial the same warm-up procedure was conducted yet the rest interval between the cessation of warm-up and exercise equaled 15 min. On the third occasion the 30 s Wingate test was performed without a warm-up. During the Wingate test the following variables were registered: total external work (W-TOT), maximal power (P-max), average power (P-AV), time of reaching P-max (TrPmax) the index of power decrement (Pdi%). Additionally the following acid-base variables were evaluated in the blood: LA, HCO3, BE and pH. \ The results of ANOVA did not show a significant effect of the 15 min warm-up on all the considered anaerobic power indices: W-TOT P-max, P-AV, TrPmax, while statistically significant effects of the warm-up were obtained in post exercise plasma LA concentration and other acid-base balance variables (p<0,001, F=13,06), HCO3 (p<0,001, F= 14,61), pH (p<0,01, F= 11, 49), BE (p < 0, 00 1, F= 14,9 7)...

Oxygen uptake kinetics and energy system’s contribution around maximal lactate steady state swimming intensity

Article

Full-text available

Feb 2017
PLOS ONE

The purpose of this study was to examine the oxygen uptake () kinetics and the energy systems’ contribution at 97.5, 100 and 102.5% of the maximal lactate steady state (MLSS) swimming intensity. Ten elite female swimmers performed three-to-five 30 min submaximal constant swimming bouts at imposed paces for the determination of the swimming velocity (v) at 100%MLSS based on a 7 x 200 m intermittent incremental protocol until voluntary exhaustion to find the v associated at the individual anaerobic threshold. kinetics (cardiodynamic, primary and slow component phases) and the aerobic and anaerobic energy contributions were assessed during the continuous exercises, which the former was studied for the beginning and second phase of exercise. Subjects showed similar time delay (TD) (mean = 11.5–14.3 s) and time constant (τp) (mean = 13.8–16.3 s) as a function of v, but reduced amplitude of the primary component for 97.5% (35.7 ± 7.3 mL.kg.min⁻¹) compared to 100 and 102.5%MLSS (41.0 ± 7.0 and 41.3 ± 5.4 mL.kg.min⁻¹, respectively), and τp decreased (mean = 9.6–10.8 s) during the second phase of exercise. Despite the slow component did not occur for all swimmers at all swim intensities, when observed it tended to increase as a function of v. Moreover, the total energy contribution was almost exclusively aerobic (98–99%) at 97.5, 100 and 102.5%MLSS. We suggest that well-trained endurance swimmers with a fast TD and τp values may be able to adjust faster the physiological requirements to minimize the amplitude of the slow component appearance, parameter associated with the fatigue delay and increase in exhaustion time during performance, however, these fast adjustments were not able to control the progressive fatigue occurred slightly above MLSS, and most of swimmers reached exhaustion before 30min swam.

Efficacy of depth jumps to elicit a post-activation performance enhancement in junior endurance runners

Article

Aug 2018
J SCI MED SPORT

Objectives: To determine the effect of performing depth jumps (DJ) pre-exercise on running economy (RE) and time to exhaustion (TTE) at the speed associated with maximal oxygen uptake (sV˙O2max) in a group of high-performing junior middle-distance runners. Design: Randomized crossover study. Methods: Seventeen national- and international-standard male distance runners (17.6±1.2years, 63.4±6.3kg, 1.76±0.06m, 70.7±5.2mLkg-1min-1) completed two trials. Following a 5min warm-up at 60% V˙O2max, participants performed a 5min run at 20%Δ below oxygen uptake corresponding with lactate turn-point to determine pre-intervention RE. Participants then completed either six DJ from a box equivalent to their best counter-movement jump (CMJ) or a control condition (C) involving body weight quarter squats. After a 10min passive recovery, another 5min sub-maximal run was performed followed by a run to exhaustion at sV˙O2max. Results: Compared to the C trial, DJ produced moderate improvements (-3.7%, 95% confidence interval for effect size: 0.25-1.09) in RE, which within the context of minimal detectable change is considered possibly beneficial. Differences in TTE and other physiological variables were most likely trivial (ES: <0.2). Individual responses were small, however a partial correlation revealed a moderate relationship (r=-0.55, p=0.028) between change in RE and CMJ height. Conclusions: The inclusion of a set of six DJ in the warm-up routine of a well-trained young male middle-distance runner is likely to provide a moderate improvement in RE.

VO2 Steady State at and Just Above Maximum Lactate Steady State Intensity

Article

Apr 2020

Over recent decades the association between metabolic and gas exchange parameters during exercise has become evident. Different “thresholds” (such as lactate thresholds, critical power, EMG thresholds) and intensity domains appear to be linked to an upper limit of oxygen uptake steady state (V̇O2SS). The aim of this study was to investigate whether MLSS is associated with the upper limit for a V̇O2SS. Forty-five subjects underwent one incremental test and 4–6 30-minute MLSS tests on a cycle ergometer. A three-component model was used to describe V̇O2 response at PMLSS and just above PMLSS+1. To evaluate the results, breath-by-breath V̇O2 and lactate (LA) values were analyzed using the intraclass correlation coefficient (ICC), increasing (k-) values and the Wilcoxon test. According to the calculated k-values of LA and VO2 at PMLSS and PMLSS+1, no significant increase of VO2 occurred during both intensities (PMLSS and PMLSS+1) from minute 10 to minute 30, confirming the existence of a V̇O2SS. Additionally, the ICC of 0.94 confirmed high accordance of the VO2 kinetics at both intensities (PMLSS and PMLSS+1). This study shows that power output at MLSS workload does not represent an accurate cut for an upper limit of V̇O2SS.

Priming exercise increases Wingate cycling peak power output

Article

Full-text available

May 2020
EUR J SPORT SCI

Purpose: The aim of the present study was to investigate the effect of priming exercise on Wingate performance and fatigue. Methods: Twelve recreationally active young male volunteers participated in the study (age: 25 ± 5 years; weight: 75.0 ± 7.5 kg; height: 177 ± 6 cm; BMI: 24.0 ± 1.7). During a first visit, participants performed a typical [Formula: see text] test and a supramaximal assessment of [Formula: see text] on a cycle ergometer, while during the next three visits, the participants performed in a random order a Wingate test (i) with no priming exercise, (ii) after priming exercise followed by a 15-min recovery (Priming15) and (iii) after priming exercise followed by a 30-min recovery (Priming30). Priming exercise lasted 6 min, at work rate corresponding to the gas exchange threshold (GET) plus 70% of the difference between the GET and [Formula: see text]. Results: The Priming 30 condition exhibited greater peak power output (595 ± 84 W) compared to the control (567 ± 85 W) and the Priming15 condition (569 ± 95 W) (P < .05). Regarding fatigue index, a tendency towards increased resistance to fatigue was observed in the Priming30 condition compared to the control and the Priming15 conditions (P = .072). Pre-Wingate lactate levels were found to be significantly different between the Priming15 (7.18 ± 3.09 mmol/L) and the Priming30 (4.87 ± 2.11 mmol/L) conditions (P < .05). Conclusions: Priming exercise of high intensity followed by a prolonged recovery leads to increased peak power in a subsequent Wingate test. Moreover, our data are consistent with the idea that a priming exercise-induced modest increase in blood lactate concentration at the onset of the following criterion bout is a key factor of performance.

Changes in the physiological strain and graded exercise performance due to warming or cooling of the lower body in a temperate environment

Article

Jan 2021
J SPORT MED PHYS FIT

Background: The effects of a reduced or mildly elevated exercising muscle temperature on the graded exercise test (GXT) performance have yet to be studied. The present study clarified the effects of a range of exercising muscle temperatures on GXT performance in a temperate environment. Methods: Eight male subjects (age, 24.0±0.5 years old; height, 175±2 cm; weight, 64.8±2.0 kg; peak oxygen consumption [V̇ O2peak], 51.1±2.4 ml/kg/min) performed 4 GXTs at different exercising muscle temperatures using a cycle-ergometer in a temperate environment (24.1 ± 0.2 °C). The exercise began at 0.3 kp with 60 rpm and increased 0.3 kp every minute until volitional exhaustion. Subjects passively cooled (averaged deep thigh and calf temperature [Tmm], COLD, 31 °C or COOL, 33 °C) or warmed (Tmm; WARM, 35 °C or HOT, 37 °C) the exercising muscle using water perfusion pants throughout the test. The peak oxygen consumption (V̇ O2peak), exercise time to exhaustion (TTE), heart rate (HR), tympanic (Tty) and mean body temperature (Tb), and total sweat loss were also measured. Results: No significant differences were observed in the V̇ O2peak or TTE among the 4 conditions; however, the HR, Tb, and total sweat loss were significantly higher (p<0.05) under warming conditions than cooling conditions. Conclusions: These results suggest that although the cardiovascular and thermoregulatory strain is higher under warming conditions than cooling conditions, the exercising muscle temperature does not affect the performance of a GXT lasting approximately 15 min in a temperate environment.

Prior Heavy-Intensity Exercise Enhances VO2 Kinetics and Short-Term High-Intensity Exercise Performance Independently of Aerobic Training Status.

Article

Sep 2014

Unlabelled: Prior high-intensity exercise can improve exercise performance during severe-intensity exercise. These positive alterations have been attributed, at least in part, to enhancement of overall oxygen-uptake (VO2) kinetics. Purpose: To determine the effects of prior heavy-intensity exercise on VO2 kinetics and short-term high-intensity exercise performance in individuals with different aerobic-training statuses. Methods: Fifteen active subjects (UT; VO2max = 43.8 ± 6.3 mL · kg-1 · min-1) and 10 well-trained endurance cyclists (T; VO2max = 66.7 ± 6.7 mL · kg-1 · min-1) performed the following protocols: an incremental test to determine lactate threshold and VO2max, 4 maximal constant-load tests to estimate critical power, and two 3-min bouts of cycle exercise, involving 2 min of constant-work-rate exercise at severe intensity followed by a 1-min all-out sprint test. This trial was performed without prior intervention and 10 min after prior heavy-intensity exercise (ie, 6 min at 90% critical power). Results: The mean response time of VO2 was shortened after prior exercise for both UT (30.7 ± 9.2 vs 24.1 ± 7.2 s) and T (31.8 ± 5.2 vs 25.4 ± 4.3 s), but no group-by-condition interaction was detected. The end-sprint performance (ie, mean power output) was improved in both groups (UT ~4.7%, T ~2.0%; P < .05) by prior exercise. Conclusion: The effect of prior heavy-intensity exercise on overall VO2 kinetics and short-term high-intensity exercise performance is independent of aerobic-training status.

Effects of previous exercise with arms or legs on metabolism and performance in exhaustive exercise

Article

Full-text available

Jun 1975
J Appl Physiol

The ability of additional muscles to perform after certain other muscles of the body had been exercised to exhaustion was studied in three male subjects. Exhaustive exercise was performed in two series: series L-A, a bout of leg exercise preceded a bout of arm exercise; series A-L, arm preceded leg (6-min recovery between bouts). Biopsies were taken during the course of each experiment from both the deltoideus and vastus lateralis muscles for determination of ATP, creatine phosphate, lactate, and pyruvate. Exhaustive exercise led to marked elevations in lactate and decreases in ATP and CP in exercised muscle and marked increases in blood lactate concentration. Similar changes, especially in lactate, were observed during and after the first exercise bout in nonexercised muscle. When arm or leg exercise was performed as the second bout, decreases in performance time were observed as compared to performance as the initial bout. It is suggested that the performance potential of muscle is decreased because of internal changes elicited by elevated blood lactate and/or blood H+ concentrations brought about by other muscle groups previously exercised to exhaustion.

Linear and nonlinear characteristics of oxygen uptake during heavy exercise

Article

Full-text available

Jan 1992

We assessed the linearity of oxygen uptake (VO2) kinetics for several work intensities in four trained cyclists. VO2 was measured breath by breath during transitions from 33 W (baseline) to work rates requiring 38, 54, 85, and 100% of maximal aerobic capacity (VO2max). Each subject repeated each work rate four times over 8 test days. In every case, three phases (phases 1, 2, and 3) of the VO2 response could be identified. VO2 during phase 2 was fit by one of two models: model 1, a double exponential where both terms begin together close to the start of phase 2, and model 2, a double exponential where each of the exponential terms begins independently with separate time delays. VO2 rose linearly for the two lower work rates (slope 11 ml.min-1 W-1) but increased to a greater asymptote for the two heavier work rates. In all four subjects, for the two lighter work rates the double-exponential regression reduced to a single value for the time constant (average across subjects 16.1 +/- 7.7 s), indicating a truly monoexponential response. In addition, one of the responses to the heaviest work rate was monoexponential. For the remaining seven biexponential responses to the two heaviest work rates, model 2 produced a significantly better fit to the responses (P less than 0.05), with a mean time delay for the slow component of 105 +/- 46 s.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of work rate on ventilatory and gas exchange kinetics

Article

Full-text available

Sep 1989

A linear system has the property that the kinetics of response do not depend on the stimulus amplitude. We sought to determine whether the responses of O2 uptake (VO2), CO2 output (VCO2), and ventilation (VE) in the transition between loadless pedaling and higher work rates are linear in this respect. Four healthy subjects performed a total of 158 cycle ergometer tests in which 10 min of exercise followed unloaded pedaling. Each subject performed three to nine tests at each of seven work rates, spaced evenly below the maximum the subject could sustain. VO2, VCO2, and VE were measured breath by breath, and studies at the same work rate were time aligned and averaged. Computerized nonlinear regression techniques were used to fit a single exponential and two more complex expressions to each response time course. End-exercise blood lactate was determined at each work rate. Both VE and VO2 kinetics were markedly slower at work rates associated with sustained blood lactate elevations. A tendency was also detected for VO2 (but not VE) kinetics to be slower as work rate increased for exercise intensities not associated with lactic acidosis (P less than 0.01). VO2 kinetics at high work rates were well characterized by the addition of a slower exponential component to the faster component, which was seen at lower work rates. In contrast, VCO2 kinetics did not slow at the higher exercise intensities; this may be the result of the coincident influence of several sources of CO2 related to lactic acidosis. These findings provide guidance for interpretation of ventilatory and gas exchange kinetics.

Linear model of muscle respiration explains monoexponential phosphocreatine changes

Article

Full-text available

May 1988
Am J Physiol

Ronald Meyer

Phosphocreatine (PCr) content was measured by phosphorus nuclear magnetic resonance spectroscopy in the gastrocnemius muscles of pentobarbital-anesthetized rats during and after twitch stimulation at rates up to 0.75 Hz. The monoexponential time constant for PCr changes was similar at the onset of vs. during recovery after stimulation and was not significantly different for different stimulation rates (mean time constant 1.44 min). Steady-state PCr level during stimulation was linearly related to the product of stimulation rate times peak twitch force. These results are shown to be consistent with a simple first-order electrical analog model of oxidative metabolism that is applicable at submaximal oxidative rates. The model assumes equilibrium of the creatine kinase reaction, which is modeled as a chemical capacitor, with capacitance proportional to the total creatine level, and PCr level proportional to the cytosolic free energy of ATP hydrolysis.

Muscle power and metabolism in maximal intermittent exercise

Article

Full-text available

May 1986

Muscle power and the associated metabolic changes in muscle were investigated in eight male human subjects who performed four 30-s bouts of maximal isokinetic cycling at 100 rpm, with 4-min recovery intervals. In the first bout peak power and total work were (mean +/- SE) 1,626 +/- 102 W and 20.83 +/- 1.18 kJ, respectively; muscle glycogen decreased by 18.2 mmol/kg wet wt, lactate increased to 28.9 +/- 2.7 mmol/kg, and there were up to 10-fold increases in glycolytic intermediates. External power and work decreased by 20% in both the second and third exercise periods, but no further change occurred in the fourth bout. Muscle glycogen decreased by an additional 14.8 mmol/kg after the second exercise and thereafter remained constant. Muscle adenosine triphosphate (ATP) was reduced by 40% from resting after each exercise period; creatine phosphate (CP) decreased successively to less than 5% of resting; in the recovery periods ATP and CP increased to 76 and 95% of initial resting levels, respectively. Venous plasma glycerol increased linearly to 485% of resting; free fatty acids did not change. Changes in muscle glycogen, lactate, and glycolytic intermediates suggested rate limitation at phosphofructokinase during the first and second exercise periods, and phosphorylase in the third and fourth exercise periods. Despite minimal glycolytic flux in the third and fourth exercise periods, subjects generated 1,000 W peak power and sustained 400 W for 30 s, 60% of the values recorded in the first exercise period.(ABSTRACT TRUNCATED AT 250 WORDS)

Human muscle metabolism during intermittent maximal exercise

Article

Full-text available

Sep 1993

Eight male subjects volunteered to take part in this study. The exercise protocol consisted of ten 6-s maximal sprints with 30 s of recovery between each sprint on a cycle ergometer. Needle biopsy samples were taken from the vastus lateralis muscle before and after the first sprint and 10 s before and immediately after the tenth sprint. The energy required to sustain the high mean power output (MPO) that was generated over the first 6-s sprint (870.0 +/- 159.2 W) was provided by an equal contribution from phosphocreatine (PCr) degradation and anaerobic glycolysis. Indeed, within the first 6-s bout of maximal exercise PCr concentration had fallen by 57% and muscle lactate concentration had increased to 28.6 mmol/kg dry wt, confirming significant glycolytic activity. However, in the tenth sprint there was no change in muscle lactate concentration even though MPO was reduced only to 73% of that generated in the first sprint. This reduced glycogenolysis occurred despite the high plasma epinephrine concentration of 5.1 +/- 1.5 nmol/l after sprint 9. In face of a considerable reduction in the contribution of anaerobic glycogenolysis to ATP production, it was suggested that, during the last sprint, power output was supported by energy that was mainly derived from PCr degradation and an increased aerobic metabolism.

Influence of muscle fiber type and pedal frequency on oxygen uptake kinetics of heavy exercise

Article

Full-text available

Oct 1996

We tested the hypothesis that the amplitude of the additional slow component of O2 uptake (VO2) during heavy exercise is correlated with the percentage of type II (fast-twitch) fibers in the contracting muscles. Ten subjects performed transitions to a work rate calculated to require a VO2 equal to 50% between the estimated lactate (Lac) threshold and maximal VO2 (50% delta). Nine subjects consented to a muscle biopsy of the vastus lateralis. To enhance the influence of differences in fiber type among subjects, transitions were made while subjects were pedaling at 45, 60, 75, and 90 rpm in different trials. Baseline VO2 was designed to be similar at the different pedal rates by adjusting baseline work rate while the absolute increase in work rate above the baseline was the same. The VO2 response after the onset of exercise was described by a three-exponential model. The relative magnitude of the slow component at the end of 8-min exercise was significantly negatively correlated with % type I fibers at every pedal rate (r = 0.64 to 0.83, P < 0.05-0.01). Furthermore, the gain of the fast component for VO2 (as ml.min-1.W-1) was positively correlated with the % type I fibers across pedal rates (r = 0.69-0.83). Increase in pedal rate was associated with decreased relative stress of the exercise but did not affect the relationships between % fiber type and VO2 parameters. The relative contribution of the slow component was also significantly negatively correlated with maximal VO2 (r = -0.65), whereas the gain for the fast component was positively associated (r = 0.68-0.71 across rpm). The amplitude of the slow component was significantly correlated with net end-exercise Lac at all four pedal rates (r = 0.64-0.84), but Lac was not correlated with % type I (P > 0.05). We conclude that fiber type distribution significantly affects both the fast and slow components of VO2 during heavy exercise and that fiber type and fitness may have both codependent and independent influences on the metabolic and gas-exchange responses to heavy exercise.

Muscle O2 uptake kinetics in humans: Implications for metabolic control

Article

Full-text available

Apr 1996

Muscle O2 uptake (VO2) kinetics in response to an augmented energetic requirement (on-transition) has never been directly determined in humans. We have developed a constant-infusion thermodilution technique that allowed rapid measurements of leg blood flow (Qleg) and, in conjunction with frequent serial measurement of arteriovenous O2 content difference across the leg [(Ca - Cv)O2leg], permitted the determination of the VO2 of the leg (VO2leg) at 3- to 4-s time intervals. VO2leg kinetics during the on-transition was taken as a close approximation of muscle VO2 (VO2mus) kinetics. Alveolar VO2 (VO2A), Qleg, leg O2 delivery [(Q.CaO2leg)], (Ca - Cv)O2leg, and VO2leg kinetics were determined in six trained subjects [age 22.8 +/- 4.4 (SD) yr; maximal O2 uptake 59.1 +/- 5.3 ml.kg-1.min-1] during the transition from unloaded pedaling to a workload (loaded pedaling; LP) (183 +/- 20 W) well below the previously determined ventilatory threshold. For all variables, two distinct phases were recognized. During the first 10-15 s of loaded pedaling (phase I), VO2A, Qleg, and (Q.CaO2)leg increased rapidly, whereas VO2leg increased only slightly and (Ca - Cv)O2leg actually decreased. After phase I, all variables showed a monoexponential increase (phase II), with similar time courses [slightly faster for (Ca - CV)O2leg]. In a consideration of both phases, the half times of the responses among variables were not significantly different: 25.5 +/- 2.6 s for VO2A, 26.6 +/- 7.6 s for Qleg, 26.9 +/- 8.3 s for (Q.CaO2leg, 23.5 +/- 1.3 s for (Ca - Cv)O2leg, and 27.9 +/- 5.7 s for VO2leg. We conclude that during the on-transition the kinetics of VO2A and VO2leg, as measured by these methods, are similar. The analysis of the early phase (first 10-15 s) of the on-transition indicates that bulk delivery of O2 to the working muscles is not limiting VO2leg kinetics. However, the present results cannot discriminate between maldistribution of blood flow/VO2 vs. inertia the intracellular oxidative machinery as the limiting factor.

Effects of hypoxic hypoxia on O2 uptake and heart rate kinetics during heavy exercise

Article

Full-text available

Jan 1997

It is unclear whether hypoxia alters the kinetics of O2 uptake (VO2) during heavy exercise [above the lactic acidosis threshold (LAT)] and how these alterations might be linked to the rise in blood lactate. Eight healthy volunteers performed transitions from unloaded cycling to the same absolute heavy work rate for 8 min while breathing one of three inspired O2 concentrations: 21% (room air), 15% (mild hypoxia), and 12% (moderate hypoxia). Breathing 12% O2 slowed the time constant but did not affect the amplitude of the primary rise in VO2 (period of first 2-3 min of exercise) and had no significant effect on either the time constant or the amplitude of the slow VO2 component (beginning 2-3 min into exercise). Baseline heart rate was elevated in proportion to the severity of the hypoxia, but the amplitude and kinetics of increase during exercise and in recovery were unaffected by level of inspired O2. We conclude that the predominant effect of hypoxia during heavy exercise is on the early energetics as a slowed time constant for VO2 and an additional anaerobic contribution. However, the sum total of the processes representing the slow component of VO2 is unaffected.

Effect of varied lactate levels on bicycle ergometer performance

Article

Aug 1984

Six subjects exercised on the bicycle ergometer on three separate occasions. Each of the three tests that each subject performed consisted of a 5-min work period [95% maximal O2 uptake (VO2max)], followed by a 4-min rest period, and then a performance task to exhaustion (90% VO2max). Each test varied only in the inspired O2 fraction (FIO2) (16, 21, or 60% O2 in N2) that was breathed during the initial 5-min work period. The remainder of each test was carried out with 21% O2. Total power output was the same for each subject during the initial 5-min work bout. However, the varied FIO2 breathed during this initial work period resulted in significantly different mean blood lactate (and H+) concentrations at the start of the performance task (P less than 0.05). Mean performance time was significantly greater (P = 0.04) after the hyperoxic treatment (14.8 min) when compared with the hypoxic (9.1 min). Mean blood lactate and H+ levels at exhaustion were not significantly different. These data demonstrate that when various blood (or muscle) lactate and H+ levels were induced on different occasions by leg muscles, the subsequent performance of those muscles was significantly affected.

Physiological determinants of pulmonary gas exchange kinetics during exercise

Article

Jan 1999
Med Sci Sports

Dynamics of pulmonary gas exchange during exercise

Article

Jan 1980

Kinetics of Metabolic Transients During Exercise

Article

Nov 1980

The present article reviews some recent work in the kinetics of mobilization of anerobic and oxidative energy upon the onset and offset of exercise in isolated muscle preparations as well as in intact animals and man. It is concluded that at the onset of a rectangular electric stimulation and/or exercise, anaerobic glycolysis sets in with a variable time delay that depends on work intensity and temperature. The adjustment of muscular blood flow (MBF) upon a square wave of exercise is very fast both in the isolated dog gastrocnemius (t 1/2 =9 s) and in human muscles (t 1/2 = 5 to 10 s). Training increases considerably the speed of adjustment. At work onset, O2 consumption is rate limited by a single first order reaction the kinetics of which, determined by the half time of the V(O2) on response (t 1/2 V(O2) on) is approximately 17 s both for isolated dog gastrocnemii stimulated with trains of short tetani and for intact running dogs. The t 1/2 V(O2) on varies in man (18 to 90 s) accompanied by a variable transient 'early' lactate accumulation related to the variable depletion of body oxygen stores, t 1/2 V(O2) on is shortest (18 s) for trained muscles that are also characterized by lower 'early' lactate release. t 1.2 V(O2) on of muscles with artificially depleted PC and O2 stores is 12 to 26 s and reflects the true kinetics of mobilization of oxidative energy. Defects of various steps along the glycolytic pathway can be assessed by measurement of t 1/2 V(O2) on and 'early' lactate.

Effect of prior exercise on &OV0312;O2 slow component is not related to muscle temperature

Article

Oct 2002
MED SCI SPORT EXER

KOPPO, K., A. M. JONES, L. VANDEN BOSSCHE, and J. BOUCKAERT. Effect of prior exercise on V̇O2 slow component is not related to muscle temperature. Med. Sci. Sports Exerc., Vol. 34, No. 10, pp. 1600–1604, 2002. Introduction: It has been widely reported that the V̇O2 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 V̇O2 slow component. Therefore, the aim of this study was to investigate whether the effect of prior heavy exercise on the V̇O2 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% V̇O2peak, 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°C and 37.2 ± 0.3°C, respectively). The V̇O2 slow component (measured as ΔV̇O2 (6-2 min)) was reduced by 57% after prior heavy exercise (P < 0.05), whereas no significant reduction was observed after prior passive warming-up. Conclusions: The results of this study indicate that the reduction in V̇O2 slow component observed after prior heavy exercise cannot be explained by an increase in muscle temperature of the upper legs.

EFFECTS OF FACIAL COLD STIMULATION ON PULMONARY VO2 AND FEMORAL ARTERY BLOOD FLOW KINETICS DURING REPEATED BOUTS OF HEAVY KNEE EXTENSION EXERCISE

Article

May 2001
MED SCI SPORT EXER

Simple interpretation of metal/wurtzite–GaN barrier heights

Article

Jul 1999

Victor Bermudez

Photoemission data for the dependence of the Schottky barrier height on the metal work function, for n-type wurtzite GaN, are discussed in terms of the Cowley–Sze model [J. Appl. Phys. 36, 3212 (1965)] for a uniform density of surface states in the band gap. It is suggested that, in the context of this model, such barrier heights can be expressed largely as a sum of the “bare-surface barrier height” (i.e., the band bending before contact formation) and a Mott–Schottky term. © 1999 American Institute of Physics.

Effects of prior exercise on pulmonary gas exchange kinetics during high-intensity exercise in humans

Article

Jan 1996
J Appl Physiol

The slow component of O2 uptake is not accompanied by changes in muscle EMG during repeated bouts of heavy exercise in humans

Article

Aug 2004
J PHYSIOL-LONDON

• We hypothesized that either the recruitment of additional muscle motor units and/or the progressive recruitment of less efficient fast-twitch muscle fibres was the predominant contributor to the additional oxygen 1uptake ( V˙O2 ) observed during heavy exercise. Using surface electromyographic (EMG) techniques, we compared the V˙O2 response with the integrated EMG (iEMG) and mean power frequency (MPF) response of the vastus lateralis with the V˙O2 response during repeated bouts of moderate (below the lactate threshold, LT) intensity cycle ergometer exercise. • Seven male subjects (age 29 ± 7 years, mean ±s.d.) performed three transitions to a work rate (WR) corresponding to 90 % LT and two transitions to a work rate that would elicit a V˙O2 corresponding to 50 % of the difference between peak V˙O2 and the LT (i.e. Δ50 %, >LT1 and >LT2). • The V˙O2 slow component was significantly reduced by prior heavy intensity exercise (>LT1, 410 ± 196 ml min−1; >LT2, 230 ± 191 ml min−1). The time constant (), amplitude (A) and gain ( ΔV˙O2/ΔWR ) of the primary V˙O2 response (phase II) were not affected by prior heavy exercise when a three-component, exponential model was used to describe the V˙O2 response. • Integrated EMG and MPF remained relatively constant and at the same level throughout both >LT1 and >LT2 exercise and therefore were not associated with the V˙O2 slow component. • These data are consistent with the view that the increased O2 cost (i.e. V˙O2 slow component) associated with performing heavy exercise is coupled with a progressive increase in ATP requirements of the already recruited motor units rather than to changes in the recruitment pattern of slow versus fast-twitch motor units. Further, the lack of speeding of the kinetics of the primary V˙O2 component with prior heavy exercise, thought to represent the initial muscle V˙O2 response, are inconsistent with O2 delivery being the limiting factor in V˙O2 kinetics during heavy exercise.

Human muscle metabolism during intermittent maximal exercise

Article

Jan 1993

Georgios C. Gaitanos

A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.

Effects of active, passive or no warm-up on the physiological response to heavy exercise

Article

Apr 1979
Eur J Appl Physiol Occup Physiol

Six endurance-trained young men were subjected to a 4 min maximal aerobic treadmill run (100% of VO2 max), after active or passive warm-up or rest on separate days. The increase in body temperature during the active and passive warm-up was controlled, so that the temperature reached the same level, before the subject was exposed to the maximal exercise. On average the rectal temperature rose to 38.3 degrees C (range 38.1-38.6 degrees C). The standard work resulted in a significant higher oxygen uptake, lower lactate concentration and higher blood pH when the work was preceded by active warm-up as compared with passive or no warm-up. The difference in total oxygen uptake during the run between the active and passive warm-up procedure was 0.8 1. No significant difference in minute volume of expired air or respiratory quotient was found. It is concluded that the physiological effects of a thorough active warm-up may be of substantial benefit to athletic performance.

Effects of specific muscle training on VO2-on response and early blood lactate

Article

Nov 1979

The relationship between half time of the O2 uptake on-response (t1/2 VO2on, seconds) and early blood lactate accumulation (delta Lab, mmol.1(-1) at the onset of submaximal arm and/or leg exercise was the object of a cross-sectional study of sedentary subjects (S,n = 3), and kayakers (K, n = 8), and of a longitudinal study on 11 untrained subjects of specific arm vs. leg training. In supine arm cranking (W = 125 watts) S had an average t1/2 VO2on of 82 s and a delta Aab of 9.2 mmol.1(-1) compared to 47 +/- 7 s and 4 +/- 1.4 mmol.1(-1), respectively, for K. In longitudinal trainees shorter t1/2 VO2on was accompanied by lower Lab for the trained limbs. Specific limb conditioning in swimmers and runners resulted in shorter t1/2 VO2on. A linear relationship was observed between delta Lab and t1/2 VO2on having an intercept on the time axis at congruent to 20 s and a slope proportional to muscle mass. Trained muscles were grouped closest to the intercept indicating local acceleration of the rate of O2 transfer approaching the t1/2 VO2on for isolated perfused muscle at the onset of work. Since t1/2 VO2on, we conclude that factors distal to the capillary are specifically involved in the local training response.

Effects of severe prior exercise on assessment of maximal oxygen uptake

Article

May 1978

Five moderately fit males (50.8 ml.kg-1.min-1) performed 14 continuous type VO2 max tests on a motor-driven treadmill. Randomly assigned experimental sessions, consisting of three tests each and separated by 10 (tests 1, 2, 3), 20 (tests 4, 5, 6), 30 (tests 7, 8, 9), or 40 (tests 10, 11, 12) min, were conducted at a consistent hour for each subject every 4th day. Two separately performed tests were also included in the random assignment with the test eliciting the highest VO2 max value designated as the standard reference (SR). VO2 max values for tests 1 through 12 were not significantly different from the SR in spite of elevated pretest blood lactate concentrations ranging from 5 mM to 16 mM. Performance time was reduced for all tests other than tests 1, 4, 7, and 10, reaching the level of statistical significance (P less than 0.05) in tests 2, 3, 5, 6, and 9. It was concluded that valid and reliable assessment of VO2 max is possible even though testing is initiated with subjects in varying stages of exhaustion.

Effect of warm-up on metabolic responses to strenuous exercise

Article

Feb 1975
Med Sci Sports

Aerobic and anaerobic energy transformations were measured in two trained runners during 90-sec treadmill runs at 23.6 km/hr (2% grade). The runs were preceded by rest or either of two warm-ups: 1) 15-min run at 10 km/hr, or 2) 15-min run at 10 km/hr followed by 3-min standing. Compared with runs without warm-up, during the third half minute of runs following both types of warm-up 11% greater heart rates (HR), 8% greater oxygen consumption (Vo2), and unchanged ventilation were recorded. The rate constant of the approach of Vo2 to O2 in the first minute of work was unaffected by warm-up. Runs following either warm-up resulted in 25% lower lactate production; during these runs 3 to 4 degrees C higher gastrocnemius muscle temperatures (Tm) were maintained. The differences in HR, Vo2, and Tm continued throughout exhausting 5-min runs at 20.9 km/hr (2% grade). An elevated muscle temperature may therefore be requisite for the maximal aerobic response to a short exhausting run.

Asymmetries of oxygen uptake transients at the on- and offset of heavy exercise in humans

Article

Dec 1991

1. At work rates which do not result in a sustained increase in blood lactate ([L-]), oxygen uptake (VO2) approaches the steady state with first-order kinetics. However, when [L-] is increased, at least two kinetic components are required to characterize the VO2 response dynamics. The purpose of the present investigation was to determine whether these more-complex kinetics are best represented as: (a) two components which operate throughout the exercise or (b) a delayed slow component which is consequent to the lactic acidaemia and which does not influence the early development of the O2 deficit. 2. Six healthy subjects underwent an incremental ramp test on a cycle ergometer, to the limit of tolerance, for determination of the maximum VO2 (micro VO2) and and estimation [symbol: see text] of the threshold for lactic acidaemia (theta L) non-invasively. Subjects then performed, on different days, two to four repetitions of square-wave exercise from a baseline of unloaded pedalling ('O' Watts (W)) to work rates (WR) less than theta L (90% theta L) and greater than theta L (half-way between theta L and micro VO2). Ventilatory and pulmonary gas exchange variables were determined breath-by-breath. For each subject, the VO2 transitions were averaged prior to fitting a least-squares algorithm to the on- and off-transient responses. 3. The less than theta L test resulted in a mono-exponential VO2 response, with a time constant of 31.3 and 31.5 s for the on- and off-transients, respectively. 4. The VO2 responses to the greater than theta L test were fitted to three competing models: (a) a single exponential for the entire period; (b) a double exponential for the entire period; and (c) an initial single exponential with a subsequent phase of delayed onset. Model (c) yielded a significantly lower residual mean-squares error than methods (a) and (b), with a time constant for the initial component of 40.2 s for the on-transient and 32.9 s for the off-transient and a subsequent phase of VO2 increase for the on-transient which averaged 230 ml min-1. The delta VO2/delta WR for the early kinetics of the greater than theta L test were not different from the less than theta L test (9.6 and 9.5 ml min-1 W-1, respectively). 5. These data suggest that the slow phase of the greater than theta L VO2 kinetics is a delayed-onset process. This being the case, the O2 deficit during heavy exercise, as conventionally estimated, would be overestimated.

Dependence of the mean power frequency of the electromyogram on muscle force and fibre type

Article

Sep 1991

The aim of this study was to investigate whether the mean power frequency of the electromyogram of the knee extensors was force and/or muscle fibre-type dependent. Ten female subjects performed a gradually increasing static knee extension (5 seconds duration) using an isokinetic dynamometer. Electromyogram-signals were obtained from the vastus lateralis, vastus medialis and the rectus femoris muscles. The torque signal and the three electromyogram signals were recorded on a tape recorder. From the electromyogram recordings the mean power frequency and the signal amplitude were determined. Muscle biopsies were later obtained from the right vastus lateralis and stained for alkaline and acid mATPase for the determination of fibre-type proportion and areas. Both the mean power frequencies and the signal amplitudes of the three knee extensors were positively torque dependent. Furthermore it was found that the fibre type proportion and the regression coefficient of the torque (%)-mean power frequency relationship were positively correlated. Also a negative correlation existed between the type-1 (%) proportion and the intercept of the individual torque (%)-mean power frequency relationships. In contrast to proposed models of the electromyogram signal no correlation was found between the mean power frequency and the fibre area.

Effects of warm-up on muscle glycogenolysis during intense exercise

Article

Feb 1991
MED SCI SPORT EXER

This study investigated the effects of preliminary exercise (warm-up) on glycogen degradation and energy metabolism during intense cycle ergometer exercise. After determination of VO2max, six male subjects were randomly assigned to perform warm-up (WU) and no warm-up (NWU) trials incorporating a 2 min standardized sprint ride (SR) at 120% of the power output attained at VO2max (POmax). Muscle biopsies and temperature (Tm) recordings were obtained from the vastus lateralis muscle. Tm was elevated above the resting level prior to the SR during the WU trial (37.7 +/- 0.1 vs 35.4 +/- 0.4 degrees C; P less than 0.05) and remained higher than the NWU trial after the SR (38.6 +/- 0.2 vs 37.1 +/- 0.4 degrees C; P less than 0.05). Similar trends existed for rectal temperature (Tr). The increases in Tm and Tr during the SR were both greater in the NWU trial (P less than 0.05). Muscle glycogen degradation was similar for the WU and NWU trials (30.8 +/- 3.7 vs 25.6 +/- 3.7 mmol.kg-1, respectively). When blood and muscle lactate concentrations after the SR were expressed relative to values before the SR, the WU trial resulted in a lower accumulation of blood lactate (6.5 +/- 0.9 vs 10.7 +/- 0.8 mEq.l-1; P less than 0.01) and muscle lactate (20.1 +/- 0.1 vs 23.4 +/- 2.2 mEq.kg-1 wet wt.; P less than 0.05). Furthermore, oxygen consumption during the 1st min of the SR was higher in the WU trial (2.3 +/- 0.2 vs 1.9 +/- 0.2 l.min-1; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Warm-Up on Blood Gases, Lactate and Acid-Base Status During Sprint Swimming

Article

Sep 1990

A standardized 200-m front crawl sprint swim (SpS) was used to evaluate the effects of warm-up on pH, blood gases, and the concentrations of lactate ([La-]) and bicarbonate ([HCO3-]) in arterialized and venous blood. Eight trained male swimmers performed two randomly assigned 200-m front crawl swims at previously determined intensities corresponding to 120% VO2max. One swim was preceded by a warm-up (WU trial) which consisted of a 400-m front crawl swim (82% VO2max), 400-m flutter kicking (45% VO2max), and 4 x 50-m front crawl sprints (111% VO2max). The second was performed without warm-up (NWU trial). Blood was sampled from a hyperemized earlobe and an antecubital vein before the warm-up, 9 min after the warm-up (1 min before the swim), immediately following the SpS, and at 2, 5, 10, and 20 min after the SpS. The warm-up exercise resulted in a higher pre-SpS [La-] in arterialized blood (3.1 +/- 0.4 and 1.7 +/- 0.4 mmol x l-1, p less than 0.05), a higher hydrogen ion concentration ([H+]) in venous blood (45.9 +/- 0.9 and 42.2 +/- 0.8 nmol x l-1, p less than 0.001), and a lower arterialized blood [HCO3-] (25.1 +/- 0.9 and 22.2 +/- 0.8 mmol x l-1, p less than 0.05). The SpS was accompanied with higher heart rates during the WU trial (178 +/- 3 and 169 +/- 3 bpm; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of muscle and pulmonary O2 uptake by circulatory dynamics during exercise

Article

Apr 1990

The effect of cardiovascular adjustments on the coupling of cellular to pulmonary gas exchange during unsteady states of exercise remains controversial. Computer simulations were performed to assess these influences on O2 delivery and pulmonary O2 uptake (pVO2). Algorithms were developed representing muscle and "rest-of-body" compartments, connected in parallel by arterial and venous circulations to a pump-and-lungs compartment. Exercise-induced increases in VO2 and cardiac output went to the muscle compartment. Model parameters [e.g., time constants for blood flow and muscle O2 uptake (mVO2)] could be varied independently. Simulation results demonstrated that 1) the rise in pVO2 during exercise contains three phases; 2) the contribution of changes in venous O2 stores to pVO2 kinetics and the O2 deficit occur almost entirely in phase 1; 3) under a wide variety of manipulations, the kinetics of pVO2 in phase 2 were within a couple of seconds of that assigned to mVO2 (i.e., there is not an obligatory slowing of VO2 kinetics at the lungs relative to those at the muscles; 4) by use of available estimates of blood flow adjustment, O2 delivery would not limit mVO2 after exercise onset; and 5) blood flow could limit O2 delivery in recovery, if blood flow returned to base-line levels at rates similar to those during the on-transient phase.

Physiological determinants of pulmonary gas exchange kinetics during exercise

Article

Mar 1990
MED SCI SPORT EXER

We consider how the optimal selection of the profile of imposed work rate, coupled with rigorous, statistically justified analysis of the pattern of the pulmonary gas exchange response, makes it possible to assemble a control model incorporating the proportional role of the muscle, circulation, and gas stores. Gains, time constants, and delays may be assigned to the components of the response and its linearity assessed. These techniques also allow the investigator to examine the features of poorly understood and even unexpected response patterns. Recent interest in the analysis of the non-steady state of exercise-in normal subjects and in patients with gas exchange defects-has led to an improved understanding of the sub-threshold dynamics. At work rates above the lactate threshold, the more complex kinetics are to date poorly described, and hence poorly understood, remaining a fertile area for the application of control-systems techniques to exercise.

Inhibition of rabbit skeletal muscle contraction by hydrogen ions and phosphate

Article

Feb 1988

1. The effects of phosphate and protons on the mechanics and energetics of muscle contraction have been investigated using glycerinated rabbit psoas muscle. 2. Fibres were fully activated by addition of Ca2+ (pCa 4-5) at 10 degrees C. The velocities of contraction were measured in isotonic load clamps, and the velocities of unloaded fibres were measured by applying a series of step changes in fibre length. Fibre ATPase activity was monitored using an enzyme system to couple ADP production to reduced nicotinamide-adenine dinucleotide (NADH) and measuring the depletion of NADH by optical density. 3. At pH 7.0 and 3 mM-phosphate, isometric tension (P0) was 13.2 +/- 0.9 N/cm (mean +/- S.E.M., n = 10 observations), the maximum contraction velocity (Vmax) was 1.63 +/- 0.05 lengths/s (n = 5) and the ATPase activity was 1.27 +/- 0.12 s-1 myosin head-1 (n = 35). Increasing phosphate from 3 to 20 mM at pH 7.0 does not affect Vmax, causes a small decrease in the ATPase activity (15-20%) and decreases P0 by approximately 20%. Changing pH from 7 to 6 at 3 mM-phosphate decreases P0 by 45% and both Vmax and ATPase activity by 25-30%. The effects of changing both pH and phosphate were approximately additive for all parameters measured. The inhibition of these parameters by low pH and high concentration of phosphate was reversible. 4. The force-velocity relation was fitted by the Hill equation using a non-linear least-squares method. The value of the parameter which describes the curvature, a/P0, was 0.20. The curvature of the force-velocity relation was not changed by addition of phosphate or by changes in pH. 5. These data provide information on both the kinetics of the actomyosin interaction and on the process of muscle fatigue. The data are consistent with models of cross-bridge kinetics in which phosphate is released within the powerstroke in a step involving a rapid equilibrium between states. The inhibition by protons is more complex, and may involve less specific effects on protein structure. 6. During moderate fatigue of living skeletal muscle, MgATP concentration is known to remain approximately constant at 4 mM, phosphate to increase from 3 to 20 mM, and protons from 0.1 to 1 microM. The data suggest that much of the inhibition of P0 observed during moderate fatigue can be explained by the increased levels of phosphate and protons, and that much of the inhibition of fibre Vmax and ATPase activity can be explained by the increase in protons.

Effect of prior exercise on maximal short-term power output in man

Article

Nov 1987

The effect of prior exercise (PE) on subsequent maximal short-term power output (STPO) was examined during cycling exercise on an isokinetic ergometer. In the first series of experiments the duration of PE at a power output equivalent to 98% maximum O2 uptake (VO2max) was varied between 0.5 and 6 min before measurement of maximal STPO. As PE duration increased subsequent STPO fell to approximately 70% of control values after 3-6 min. In series ii the effect of varying the intensity of PE of fixed 6-min duration was studied in five subjects. After PE less than 60% VO2max there was an increase of 12% in STPO, but after greater than 60% VO2max there was a progressive fall in STPO as PE intensity increased, indicating a reduction of approximately 35% at 100% VO2max compared with control values. In series iii we examined the effect on STPO of allowing a recovery period after a fixed intensity (mean = 87% VO2max) of 6 min PE before measurement of STPO. This indicated a rapid recovery of dynamic function with a half time of approximately 32 s, which is similar to the kinetics of PC resynthesis and taken with the other findings suggests the dominant role that PC exerts on the STPO under these conditions.

Blood flow distribution in dog gastrocnemius muscle at rest and during stimulation

Article

Jul 1985

The distribution of blood flow within the isolated perfused dog gastrocnemius muscle (weight 100-240 g) was studied by intra-arterial injection of radioactively labeled microspheres (diameter 15 micron) at rest and during supramaximal stimulation to rhythmic isotonic tetanic contractions of varied frequency against varied loads. After the experiment the muscle was cut into 180-250 pieces of approximately 0.75 g each, and the blood flow to each muscle piece was determined from its radioactivity. The inhomogeneity of blood flow was represented as the frequency distribution of the ratios of regional specific blood flow, i.e., blood flow per unit tissue weight of the piece, QR, to the overall specific blood flow of the muscle, Q. The QR/Q values for the individual pieces of a muscle were found to vary widely both at rest and during stimulation. With rising work load the frequency distribution had a tendency to broaden and flatten, indicating increasing perfusion inhomogeneity. On the average of the experiments, there was no significant difference in specific blood flow between the three anatomic components of the gastrocnemius (lateral and medial heads of gastrocnemius and flexor digitorum superficialis) nor between the superficial and deep portions within these anatomic components, only the distal third of the muscle was relatively less perfused compared with the proximal two-thirds. The considerable inhomogeneity of blood flow as revealed by microsphere embolization and by other methods is expected to exert important limiting effects on local O2 supply, particularly during exercise. Its neglect would lead to serious errors in the analysis of O2 supply to muscle tissue.

Oxygen uptake kinetics for various intensities of constant-load work

Article

Oct 1972
J Appl Physiol

Effect of varied lactate levels on bicycle ergometer performance

Article

Sep 1984

Parameters of ventilatory and gas exchange during exercise

Article

Jul 1982

To determine the precise nonsteady-state characteristics of ventilation (VE), O2 uptake (VO2), and CO2 output (VCO2) during moderate-intensity exercise, six subjects each underwent eight repetitions of 100-W constant-load cycling. The tests were preceded either by rest or unloaded cycling ("0" W). An early component of VE, VO2, and VCO2 responses, which was obscured on any single test by the breath-to-breath fluctuations, became apparent when the several repetitions were averaged. These early responses were abrupt when the work was instituted from rest but were much slower and smaller from the 0-W base line and corresponded to the phase of cardiodynamic gas exchange. Some 20 s after the onset of the work a further monoexponential increase to steady state occurred in all three variables, the time constants of which did not differ between the two types of test. Consequently, the exponential behavior of VE, VO2, and VCO2 in response to moderate exercise is best described by a model that incorporates only the second phase of the response.

Effects of Prior Exercise on Metabolic and Gas Exchange Responses to Exercise

Abstract

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