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The Journal of Physiology Jan 2008Efforts to understand human physiology through the study of champion athletes and record performances have been ongoing for about a century. For endurance sports three... (Review)
Review
Efforts to understand human physiology through the study of champion athletes and record performances have been ongoing for about a century. For endurance sports three main factors--maximal oxygen consumption (.VO(2,max)), the so-called 'lactate threshold' and efficiency (i.e. the oxygen cost to generate a given running speed or cycling power output)--appear to play key roles in endurance performance. and lactate threshold interact to determine the 'performance .VO(2)' which is the oxygen consumption that can be sustained for a given period of time. Efficiency interacts with the performance .VO(2) to establish the speed or power that can be generated at this oxygen consumption. This review focuses on what is currently known about how these factors interact, their utility as predictors of elite performance, and areas where there is relatively less information to guide current thinking. In this context, definitive ideas about the physiological determinants of running and cycling efficiency is relatively lacking in comparison with .VO(2,max) and the lactate threshold, and there is surprisingly limited and clear information about the genetic factors that might pre-dispose for elite performance. It should also be cautioned that complex motivational and sociological factors also play important roles in who does or does not become a champion and these factors go far beyond simple physiological explanations. Therefore, the performance of elite athletes is likely to defy the types of easy explanations sought by scientific reductionism and remain an important puzzle for those interested in physiological integration well into the future.
Topics: Athletic Performance; Energy Metabolism; Exercise; Humans; Lactates; Oxygen Consumption; Physical Endurance
PubMed: 17901124
DOI: 10.1113/jphysiol.2007.143834 -
Nature Metabolism Aug 2022Measurement of oxygen consumption is a powerful and uniquely informative experimental technique. It can help identify mitochondrial mechanisms of action following... (Review)
Review
Measurement of oxygen consumption is a powerful and uniquely informative experimental technique. It can help identify mitochondrial mechanisms of action following pharmacologic and genetic interventions, and characterize energy metabolism in physiology and disease. The conceptual and practical benefits of respirometry have made it a frontline technique to understand how mitochondrial function can interface with-and in some cases control-cell physiology. Nonetheless, an appreciation of the complexity and challenges involved with such measurements is required to avoid common experimental and analytical pitfalls. Here we provide a practical guide to oxygen consumption measurements covering the selection of experimental models and instrumentation, as well as recommendations for the collection, interpretation and normalization of data. These guidelines are provided with the intention of aiding experimental design and enhancing the overall reputability, transparency and reliability of oxygen consumption measurements.
Topics: Energy Metabolism; Mitochondria; Oxygen Consumption; Reference Standards; Reproducibility of Results
PubMed: 35971004
DOI: 10.1038/s42255-022-00619-4 -
Sports Medicine (Auckland, N.Z.) Mar 2023The physiological determinants of high-intensity exercise tolerance are important for both elite human performance and morbidity, mortality and disease in clinical... (Review)
Review
The physiological determinants of high-intensity exercise tolerance are important for both elite human performance and morbidity, mortality and disease in clinical settings. The asymptote of the hyperbolic relation between external power and time to task failure, critical power, represents the threshold intensity above which systemic and intramuscular metabolic homeostasis can no longer be maintained. After ~ 60 years of research into the phenomenon of critical power, a clear understanding of its physiological determinants has emerged. The purpose of the present review is to critically examine this contemporary evidence in order to explain the physiological underpinnings of critical power. Evidence demonstrating that alterations in convective and diffusive oxygen delivery can impact upon critical power is first addressed. Subsequently, evidence is considered that shows that rates of muscle oxygen utilisation, inferred via the kinetics of pulmonary oxygen consumption, can influence critical power. The data reveal a clear picture that alterations in the rates of flux along every step of the oxygen transport and utilisation pathways influence critical power. It is also clear that critical power is influenced by motor unit recruitment patterns. On this basis, it is proposed that convective and diffusive oxygen delivery act in concert with muscle oxygen utilisation rates to determine the intracellular metabolic milieu and state of fatigue within the myocytes. This interacts with exercising muscle mass and motor unit recruitment patterns to ultimately determine critical power.
Topics: Humans; Exercise; Oxygen Consumption; Exercise Tolerance; Lung; Oxygen; Muscle, Skeletal
PubMed: 36622556
DOI: 10.1007/s40279-022-01805-w -
The British Journal of Radiology Jan 2019The concept of tumour hypoxia as a cause of radiation resistance has been prevalent for over 100 years. During this time, our understanding of tumour hypoxia has matured... (Review)
Review
The concept of tumour hypoxia as a cause of radiation resistance has been prevalent for over 100 years. During this time, our understanding of tumour hypoxia has matured with the recognition that oxygen tension within a tumour is influenced by both diffusion and perfusion mechanisms. In parallel, clinical strategies to modify tumour hypoxia with the expectation that this will improve response to radiation have been developed and tested in clinical trials. Despite many disappointments, meta-analysis of the data on hypoxia modification confirms a significant impact on both tumour control and survival. Early trials evaluated hyperbaric oxygen followed by a generation of studies testing oxygen mimetics such as misonidazole, pimonidazole and etanidazole. One highly significant result stands out from the use of nimorazole in advanced laryngeal cancer with a significant advantage seen for locoregional control using this radiosensitiser. More recent studies have evaluated carbogen and nicotinamide targeting both diffusion related and perfusion related hypoxia. A significant survival advantage is seen in muscle invasive bladder cancer and also for locoregional control in hypopharygeal cancer associated with a low haemoglobin. New developments include the recognition that mitochondrial complex inhibitors reducing tumour oxygen consumption are potential radiosensitising agents and atovaquone is currently in clinical trials. One shortcoming of past hypoxia modifying trials is the failure to identify oxygenation status and select those patient with significant hypoxia. A range of biomarkers are now available including histological necrosis, immunohistochemical intrinsic markers such as CAIX and Glut 1 and hypoxia gene signatures which have been shown to predict outcome and will inform the next generation of hypoxia modifying clinical trials.
Topics: Animals; Cell Hypoxia; Female; Humans; Male; Misonidazole; Neoplasms; Niacinamide; Oxygen Consumption; Radiation-Sensitizing Agents; Randomized Controlled Trials as Topic; Risk Assessment; Survival Analysis; Treatment Outcome; Tumor Hypoxia
PubMed: 29979089
DOI: 10.1259/bjr.20170966 -
Antioxidants & Redox Signaling Apr 2013The complexity of human DNA has been affected by aerobic metabolism, including endurance exercise and oxygen toxicity. Aerobic endurance exercise could play an important... (Review)
Review
The complexity of human DNA has been affected by aerobic metabolism, including endurance exercise and oxygen toxicity. Aerobic endurance exercise could play an important role in the evolution of Homo sapiens, and oxygen was not important just for survival, but it was crucial to redox-mediated adaptation. The metabolic challenge during physical exercise results in an elevated generation of reactive oxygen species (ROS) that are important modulators of muscle contraction, antioxidant protection, and oxidative damage repair, which at moderate levels generate physiological responses. Several factors of mitochondrial biogenesis, such as peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α), mitogen-activated protein kinase, and SIRT1, are modulated by exercise-associated changes in the redox milieu. PGC-1α activation could result in decreased oxidative challenge, either by upregulation of antioxidant enzymes and/or by an increased number of mitochondria that allows lower levels of respiratory activity for the same degree of ATP generation. Endogenous thiol antioxidants glutathione and thioredoxin are modulated with high oxygen consumption and ROS generation during physical exercise, controlling cellular function through redox-sensitive signaling and protein-protein interactions. Endurance exercise-related angiogenesis, up to a significant degree, is regulated by ROS-mediated activation of hypoxia-inducible factor 1α. Moreover, the exercise-associated ROS production could be important to DNA methylation and post-translation modifications of histone residues, which create heritable adaptive conditions based on epigenetic features of chromosomes. Accumulating data indicate that exercise with moderate intensity has systemic and complex health-promoting effects, which undoubtedly involve regulation of redox homeostasis and signaling.
Topics: Animals; Exercise; Humans; Oxidative Stress; Oxygen Consumption; Reactive Oxygen Species; Signal Transduction
PubMed: 22978553
DOI: 10.1089/ars.2011.4498 -
Trends in Endocrinology and Metabolism:... Jun 2023Distance running requires a high absolute oxygen consumption, while for a breath-hold diver the opposite is preferable. We compared physiological exercise parameters and...
Distance running requires a high absolute oxygen consumption, while for a breath-hold diver the opposite is preferable. We compared physiological exercise parameters and mitochondrial function in a competitive triathlete with those seen in an accomplished breath-hold diver and notice some remarkable differences, possibly explaining why both have become successful.
Topics: Animals; Humans; Diving; Turtles; Hares; Breath Holding; Oxygen Consumption
PubMed: 37062666
DOI: 10.1016/j.tem.2023.03.003 -
Experimental Physiology Dec 2021What is the topic of this review? The limits to maximal aerobic capacity. What advances does it highlight? A synthesis of data and ideas about what limits maximal... (Review)
Review
NEW FINDINGS
What is the topic of this review? The limits to maximal aerobic capacity. What advances does it highlight? A synthesis of data and ideas about what limits maximal aerobic capacity demonstrates the central roles of cardiac output, stroke volume and red blood cell mass in the complex physiological responses to maximal exercise. In healthy humans these factors, along with skeletal muscle blood flow, dominate systemic delivery of oxygen to the contracting muscles and set the upper limit of aerobic energy production by skeletal muscles. In elite athletes and patients with pulmonary disease the lungs can also limit oxygen uptake and delivery.
ABSTRACT
In this paper we review the physiological determinants of and discuss the role this variable plays as a determinant of endurance exercise performance. Because the ability to sustain a given pace during a competitive athletic event requires competitors to 'manage' fatigue and go as fast as possible without fatiguing prematurely, is one of the variables that sets the physiological upper limit for sustained energy production by the contracting skeletal muscles.
Topics: Cardiovascular System; Exercise; Exercise Tolerance; Humans; Muscle, Skeletal; Oxygen Consumption
PubMed: 32058638
DOI: 10.1113/EP088187 -
BMC Anesthesiology Jun 2023Body temperature (BT) is thought to have associations with oxygen consumption (VO). However, there have been few studies in which the association between systemic VO and...
BACKGROUND
Body temperature (BT) is thought to have associations with oxygen consumption (VO). However, there have been few studies in which the association between systemic VO and BT in humans was investigated in a wide range of BTs. The aims of this study were 1) to determine the association between VO and age and 2) to determine the association between VO and BT.
METHODS
This study was a retrospective study of patients who underwent surgery under general anesthesia at a tertiary teaching hospital. VO was measured by the Dräger Perseus A500 anesthesia workstation (Dräger Medical, Lubeck, Germany). The associations of VO with age and BT were examined using spline regression and multivariable regression analysis with a random effect.
RESULTS
A total of 7,567 cases were included in this study. A linear spline with one knot shows that VO was reduced by 2.1 ml/kg/min with one year of age (p < 0.001) among patients less than 18 years of age and that there was no significant change in VO among patients 18 years of age or older (estimate: 0.014 ml/kg/min, p = 0.08). VO in all bands of BT < 36.0 °C was not significantly different from VO in BT > = 36 °C and < 36.5 °C. Multivariable linear regression analysis showed that compared with VO in BT > = 36 °C and < 36.5 °C as a reference, VO levels were significantly higher by 0.57 ml/kg/min in BT > = 36.5 °C and < 37 °C (p < 0.001), by 1.8 ml/kg/min in BT > = 37 °C and < 37.5 °C (p < 0.001), by 3.6 ml/kg/min in BT > = 37.5 °C and < 38 °C (p < 0.001), by 4.9 ml/kg/min in BT > = 38 °C and < 38.5 °C (p < 0.001), and by 5.7 ml/kg/min in BT > = 38.5 °C (p < 0.001). The associations between VO and BT were significantly different among categorized age groups (p = 0.03).
CONCLUSIONS
VO increases in parallel with increase in body temperature in a hyperthermic state but remains constant in a hypothermic state. Neonates and infants, who have high VO, may have a large systemic organ response in VO to change in BT.
Topics: Infant; Infant, Newborn; Humans; Adolescent; Adult; Child, Preschool; Body Temperature; Retrospective Studies; Anesthesia, General; Fever; Oxygen Consumption; Oxygen
PubMed: 37340340
DOI: 10.1186/s12871-023-02182-1 -
The Journal of Physiology Jan 2004Fetal growth depends on the transplacental nutrient supply, which, in turn, is determined partially by the consumption and production of nutrients by the uteroplacental... (Comparative Study)
Comparative Study
Fetal growth depends on the transplacental nutrient supply, which, in turn, is determined partially by the consumption and production of nutrients by the uteroplacental tissues. In fetal sheep, the rates of growth and umbilical glucose uptake decline coincidently towards term in parallel with the normal prepartum rise in plasma cortisol. While cortisol is known to reduce growth in fetal sheep, its effects on the uteroplacental handling and delivery of nutrients remain unknown. Hence, this study, quantified the rates of umbilical uptake and uteroplacental consumption of nutrients in preterm fetuses infused with cortisol for 5 days to mimic the prepartum cortisol surge. Umbilical uptakes of glucose and lactate, but not oxygen, were significantly lower in cortisol- than saline-infused fetuses, irrespective of whether values were expressed as absolute or weight-specific rates. The rate of uteroplacental consumption of glucose, but not oxygen, was significantly higher in cortisol- than saline-infused animals. Absolute rates of uteroplacental lactate production were lower in cortisol-infused animals. When all data were combined, fetal plasma cortisol levels were positively correlated to uteroplacental glucose consumption and inversely related to umbilical glucose uptake. Cortisol treatment had no apparent effect on placental mRNA expression for the glucose transporters, GLUT-1 and GLUT-3. The results demonstrate that cortisol is physiological regulator of uteroplacental metabolism and nutrient delivery to the sheep fetus. These observations have important implications for fetal growth both in late gestation and during adverse intrauterine conditions, which raise fetal cortisol levels earlier in gestation.
Topics: Animals; Dose-Response Relationship, Drug; Female; Glucose; Hydrocortisone; Lactic Acid; Maternal-Fetal Exchange; Oxygen Consumption; Placental Circulation; Pregnancy; Sheep
PubMed: 14594988
DOI: 10.1113/jphysiol.2003.054577 -
International Journal of Sports... Mar 2022The aim of this narrative review is to provide insight as to the history, biomechanics, and physiological characteristics of competitive handcycling. Furthermore, based... (Review)
Review
The aim of this narrative review is to provide insight as to the history, biomechanics, and physiological characteristics of competitive handcycling. Furthermore, based upon the limited evidence available, this paper aims to provide practical training suggestions by which to develop competitive handcycling performance. Handbike configuration, individual physiological characteristics, and training history all play a significant role in determining competitive handcycling performance. Optimal handcycling technique is highly dependent upon handbike configuration. As such, seat positioning, crank height, crank fore-aft position, crank length, and handgrip position must all be individually configured. In regard to physiological determinants, power output at a fixed blood lactate concentration of 4 mmol·L-1, relative oxygen consumption, peak aerobic power output, relative upper body strength, and maximal anaerobic power output have all been demonstrated to impact upon handcycling performance capabilities. Therefore, it is suggested that that an emphasis be placed upon the development and frequent monitoring of these parameters. Finally, linked to handcycling training, it is suggested that handcyclists should consider adopting a concurrent strength and endurance training approach, based upon a block periodization model that employs a mixture of endurance, threshold, interval, and strength training sessions. Despite our findings, it is clear that several gaps in our scientific knowledge of handcycling remain and that further research is necessary in order to improve our understanding of factors that determine optimal performance of competitive handcyclists. Finally, further longitudinal research is required across all classifications to study the effects of different training programs upon handcycling performance.
Topics: Bicycling; Endurance Training; Hand Strength; Humans; Oxygen Consumption; Resistance Training
PubMed: 35130511
DOI: 10.1123/ijspp.2021-0458