The major functions of the respiratory system are to allow the movement and exchange of circulating air in the atmosphere to and from the lungs and to monitor and control blood acid-base balance in the body. The system is made up of multiple structures carrying out processes of ventilation, inspiration and expiration, to ensure the major functions are performed.
As the respiratory system goes through the cycle of ventilation, a partial pressure of oxygen is created. This gradient determines the oxygen transfer from atmospheric air to the mitochondria. In the atmosphere there are specific pressures of various gases, the percentage of each gas along with the atmospheric pressure determines the partial pressure that drives oxygen from high to low pressure. Oxygen diffuses through alveolar membranes in the lungs and into the blood. Oxygen dissociates from hemoglobin and diffuses into cells of muscles. (al., (2015). Oxygen is consumed at mitochondria sites in the final step of electron transport chain. (Coyle E. F., 1995) Found evidence that more mitochondria can play a role in allowing a vo2 max value to increase, however only in a very minor way, there are greater factors which affect a V02max.
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Hill et al and Herbst described VO2 max as a term for the “maximal oxygen uptake” for any given individual, it is the highest rate at which oxygen can be delivered around the body during severe exercise. (Hill, 1923). In their studies they state that a healthy human being has an upper limit to oxygen uptake, that humans have individual differences in vo2 max, that a high vo2 max is needed to be a successful middle to long distance runner recognized the importance of a high V̇O2max for elite performers (Hill A. V., 1923) and that there are limiting factors for vo2 max in a healthy human. The major limiting factor of a vo2 max is the ability of the cardiorespiratory system transportation of oxygen to the muscles. (Bassett Jr, 2000)
“This is shown by three major lines of evidence: 1) when oxygen delivery is altered (by blood doping, hypoxia, or beta-blockade), V̇O2max changes accordingly; 2) the increase in V̇O2max with training results primarily from an increase in maximal cardiac output (not an increase in the a- O2 difference); and 3) when a small muscle mass is over perfused during exercise, it has an extremely high capacity for consuming oxygen” (Bassett Jr, 2000) (BASSETT JR, Maximal oxygen uptake:“classical” versus “contemporary” viewpoints. Medicine & Science in Sports & Exercise, ., 1997.)
Although oxygen transportation is seen as the primary limiting factor in healthy exercising humans, metabolic adaptations in skeletal muscle are crucial for “improving submaximal endurance performance” (BASSETT JR, 1997.) In relation to maximal whole body exercise however literature studies prove that these are the four possible limiting factors for vo2 max in healthy humans.
- the pulmonary diffusing capacity,
- maximal cardiac output,
- oxygen carrying capacity of the blood, and
- skeletal muscle characteristics.” (BASSETT JR, 1997.)
Literature states that elite athletes generally have a higher O2 desaturation in the arteries when performing maximal full body exercise compared to regular healthy humans (Dempsey, 1984).
Fit individuals prove to have a much higher cardiac output in comparison to an untrained individual “40 vs 25 L·min−1” (Bassett Jr, 2000). Trained bodies display lower heart rate for performing the same submaximal work rate as an untrained body (Christensen, 1931). This backs up that maximal cardiac output is the major limiting factor and highlights individual differences of heathy human beings v02 max during maximal performance (Hill, 1923)
Oxygen transport to working muscles is controlled by the hemoglobin (Hb) content of the blood (Ekblom, 1976). Red blood cells are removed, stored and reinfused into the body, increasing a subjects volume of red blood cells, which is used to increase maximal aerobic [power as it increases the ability and capacity of blood to bear oxygen (APA, 1982) this level of oxygen transport impacts and limits a vo2 max. Skeletal Muscle is the final possible limitation of a v02 max, Honig et al showed evidence for “a peripheral O2 diffusion limitation in red canine muscle.” A difference in VO2 can be caused by the contractions involved in isolated muscle fibers, where mitochondria use oxygen in the final stage of the electron transport chain, creating a peripheral diffusion gradient. Differences in capillary densities can also impact a vO2 max and power output, in 1977 Andersen and Henriksson 1) stated that training can increase capillary density in a muscle. The effect training has on skeletal muscle has been proven much more than in the lung (Dempsey J. A., 1986)
V02max is not accurate predictor of the ability and capability an endurance athlete and performance, however often a high vo2 max is needed for a good endurance performance (BASSETT JR, Maximal oxygen uptake:“classical” versus “contemporary” viewpoints. Medicine & Science in Sports & Exercise, ., 1997.)acknowledged this with runners. Literature has shown that endurance can differ greatly between athletes with the same V02 max value (Coyle E. C., 1988). However Vo2 max values have proven to be useful and important to set the upper limit for endurance performance, as an athlete cannot work above Vo2 max for a prolonged time (Bassett Jr, 2000). A better predictor of endurance performance (of a runner) is their running economy, utilization of v02max along with lactate threshold (Bassett Jr, 2000). However v02 max alone is more beneficially used as a method of presenting training effects and improvements or not rather than a predictor of endurance performance rather it sets the upper limit in an endurance event (APA BASSETT & HOWLEY, May 1997). Literature states (Bassett Jr, 2000) that the plateau in V̇O2 shouldn’t be the “sole criterion for achievement of V̇O2max.“ It is recommended that secondary criteria to be used to verify a maximal effort such as “respiratory exchange ratio” and “blood lactic acid level” which can be tested in a laboratory (Bassett Jr, 2000). BASSETT JR, D.R. and HOWLEY state that these variables do “correlate with endurance performance, have been used to prescribe exercise training loads and are useful to monitor adaptation to training.” (BASSETT JR, Maximal oxygen uptake:“classical” versus “contemporary” viewpoints. Medicine & Science in Sports & Exercise, ., 1997.) Yamagata et al discovered that success in distance running may be closely related to the point at which lactate starts to accumulate in the plasma of a subject running at a certain velocity. Blood lactate measures are measured from either the fingertip or the earlobe.(Yamagata T. &., 2018)
A multi stage incremental test can be performed to collect lactate or respiratory data. An exercise such where the athlete becomes exhausted, such as cycling on an ergometer or running on a treadmill for a prolonged duration can be performed to collect such data, when the subject surpasses a certain intensity the lactate begins to accumulate exponentially.(Åstrand, 1963) (. COSTILL, 1970) Vo2 max and endurance performance has proved to be closely interlinked with the build up of blood lactate so this information can be used see the extent of physiological adaptations that were made during a period of training (Andersen, 1977.) (Bransford, 1977) The laboratory respiratory data along with blood lactate data can also be used wisely to create a specific training plan and make recommendations further training (Jones, 2006)
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