Power and peak blood lactate at 5050 m with 10 and 30 s 'all out' cycling

Effects of Altitude/Hypoxia on Single- and Multiple-Sprint Performance: A Comprehensive Review

Many sport competitions, typically involving the completion of single- (e.g. track-and-field or track cycling events) and multiple-sprint exercises (e.g. team and racquet sports, cycling races), are staged at terrestrial altitudes ranging from 1000 to 2500 m. Our aim was to comprehensively review the current knowledge on the responses to either acute or chronic altitude exposure relevant to single and multiple sprints. Performance of a single sprint is generally not negatively affected by acute exposure to simulated altitude (i.e. normobaric hypoxia) because an enhanced anaerobic energy release compensates for the reduced aerobic adenosine triphosphate production. Conversely, the reduction in air density in terrestrial altitude (i.e. hypobaric hypoxia) leads to an improved sprinting performance when aerodynamic drag is a limiting factor. With the repetition of maximal efforts, however, repeated-sprint ability is more altered (i.e. with earlier and larger performance decrements) at high altitudes (>3000-3600 m or inspired fraction of oxygen <14.4-13.3%) compared with either normoxia or low-to-moderate altitudes (<3000 m or inspired fraction of oxygen >14.4%). Traditionally, altitude training camps involve chronic exposure to low-to-moderate terrestrial altitudes (<3000 m or inspired fraction of oxygen >14.4%) for inducing haematological adaptations. However, beneficial effects on sprint performance after such altitude interventions are still debated. Recently, innovative 'live low-train high' methods, in isolation or in combination with hypoxic residence, have emerged with the belief that up-regulated non-haematological peripheral adaptations may further improve performance of multiple sprints compared with similar normoxic interventions.

Determinants of team-sport performance: implications for altitude training by team-sport athletes

Team sports are increasingly popular, with millions of participants worldwide. Athletes engaged in these sports are required to repeatedly produce skilful actions and maximal or near-maximal efforts (eg, accelerations, changes in pace and direction, sprints, jumps and kicks), interspersed with brief recovery intervals (consisting of rest or low-intensity to moderate-intensity activity), over an extended period of time (1–2 h). While performance in most team sports is dominated by technical and tactical proficiencies, successful team-sport athletes must also have highly-developed, specific, physical capacities. Much effort goes into designing training programmes to improve these physical capacities, with expected benefits for team-sport performance. Recently, some team sports have introduced altitude training in the belief that it can further enhance team-sport physical performance. Until now, however, there is little published evidence showing improved team-sport performance following altitude training, despite the often considerable expense involved. In the absence of such studies, this review will identify important determinants of team-sport physical performance that may be improved by altitude training, with potential benefits for team-sport performance. These determinants can be broadly described as factors that enhance either sprint performance or the ability to recover from maximal or near-maximal efforts. There is some evidence that some of these physical capacities may be enhanced by altitude training, but further research is required to verify that these adaptations occur, that they are greater than what could be achieved by appropriate sea-level training and that they translate to improved team-sport performance.

The lactate paradox revisited in lowlanders during acclimatization to 4100 m and in high-altitude natives

Chronic hypoxia has been proposed to induce a closer coupling in human skeletal muscle between ATP utilization and production in both lowlanders (LN) acclimatizing to high altitude and high-altitude natives (HAN), linked with an improved match between pyruvate availability and its use in mitochondrial respiration. This should result in less lactate being formed during exercise in spite of the hypoxaemia. To test this hypothesis six LN (22-31 years old) were studied during 15 min warm up followed by an incremental bicycle exercise to exhaustion at sea level, during acute hypoxia and after 2 and 8 weeks at 4100 m above sea level (El Alto, Bolivia). In addition, eight HAN (26-37 years old) were studied with a similar exercise protocol at altitude. The leg net lactate release, and the arterial and muscle lactate concentrations were elevated during the exercise in LN in acute hypoxia and remained at this higher level during the acclimatization period. HAN had similar high values; however, at the moment of exhaustion their muscle lactate, ADP and IMP content and Cr/PCr ratio were higher than in LN. In conclusion, sea-level residents in the course of acclimatization to high altitude did not exhibit a reduced capacity for the active muscle to produce lactate. Thus, the lactate paradox concept could not be demonstrated. High-altitude natives from the Andes actually exhibit a higher anaerobic energy production than lowlanders after 8 weeks of acclimatization reflected by an increased muscle lactate accumulation and enhanced adenine nucleotide breakdown.

Limiting factors to oxygen transport on Mount Everest 30 years after: a critique of Paolo Cerretelli's contribution to the study of altitude physiology

In 1976, Paolo Cerretelli published an article entitled "Limiting factors to oxygen transport on Mount Everest" in the Journal of Applied Physiology. The paper demonstrated the role of cardiovascular oxygen transport in limiting maximal oxygen consumption (VO2max). In agreement with the predominant view of VO2max limitation at that time, however, its results were taken to mean that cardiovascular oxygen transport does not limit VO2max at altitude. So it was argued that the limiting factor could be in the periphery, and muscle blood flow was proposed as a possible candidate. Despite this suggestion, the conclusion generated a series of papers on muscle structural characteristics. These experiments demonstrated a loss of muscle oxidative capacity in chronic hypoxia, and thus provided an unambiguous refutation of the then widespread hypothesis that an increased muscle oxidative capacity is needed at altitude to compensate for the lack of oxygen. This analysis is followed by a short account of Cerretelli's more recent work, with a special attention to the subject of the so-called "lactate paradox".

Acid-base balance at exercise in normoxia and in chronic hypoxia. Revisiting the "lactate paradox"

Transitions between rest and work, in either direction, and heavy exercise loads are characterized by changes of muscle pH depending on the buffer power and capacity of the tissues and on the metabolic processes involved. Among the latter, in chronological sequence: (1). aerobic glycolysis generates sizeable amounts of lactate and H(+) by way of the recently described, extremely fast (20-100 ms) "glycogen shunt" and of the excess of glycolytic pyruvate supply; (2). hydrolysis of phosphocreatine, tightly coupled with that of ATP in the Lohmann reaction, is known to consume protons, a process undergoing reversal during recovery; (3). anaerobic glycolysis sustaining ATP production in supramaximal exercise as well as in conditions of hypoxia and ischemia, is responsible for the accumulation of large amounts of lactic acid (up to 1 mol for the whole body). The handling of metabolic acids, i.e., acid-base regulation, occurs both in blood and in tissues, mainly in muscles which are the main producers and consumers of lactic acid. The role of both blood and muscle bicarbonate and non-bicarbonate buffers as well as that of lactate/H(+) cotransport mechanisms is analyzed in relation to acid-base homeostasis in the course of exercise. A section of the review deals with the analysis of the acid-base state of humans exposed to chronic hypoxia. Particular emphasis is put on anaerobic glycolysis. In this context, the so-called lactate paradox is revisited and interpreted on the basis of the most recent findings on exercise at altitude.