In all endurance sport disciplines, performance is determined by measuring the amount of oxygen in the body that can be maximally consumed to produce energy. In untrained individuals, the utilization of oxygen within muscle cells is limited and oxygen uptake is low. However, by increasing training status, oxygen metabolism within cells is progressively improved and oxygen transport through the blood becomes the limiting factor (Wagner, 2000). Thereby, the oxygen-transporting hemoglobin molecule within red blood cells plays a key role in well-trained athletes’ performance. It is important for two performance-determining mechanisms: high hemoglobin ensures a high supply of oxygen to muscle cells and an increased number of red blood cells leads to increased blood volume which, in turn, increases stroke volume during exercise. Therefore, increased hemoglobin mass (Hb-mass) improves both muscle perfusion and oxygen transport capacity. Scientific studies agree that increasing the amount of hemoglobin in the blood by 1-gram changes maximum oxygen consumption by 4 ml/min (e.g., Schmidt & Prommer, 2010). Therefore, elite endurance athletes possess > 50% more hemoglobin and whole blood than untrained people (Heinicke et al., 2001).
Endurance performance directly depends on individual Hbmass level. While the individual amount of hemoglobin is genetically determined, it can be increased by measures such as endurance training, altitude orhypoxic exposure, and illegally, through blood manipulation.
While some people may have higher hemoglobin mass (Hb-mass) because of basic genetic make-up, Hb-mass can be increased through training measures which can lead to a decisive contribution to improved performance. This adaptation process, which takes place over weeks and months, can be found in originally un- and semi-trained individuals as well as in high endurance trained world-class athletes. In un- and semi-trained subjects, the effect of endurance training on increase in Hb-mass can be up to 10% (Schmidt and Prommer, 2008). In highly trained athletes, an oscillation of 4% can be observed during a training year with maximum values being measured during the competition phase (Garvican et al., 2010). Training and injury breaks are always accompanied by a reduction in Hb-mass which has to be rebuilt during the recovery phase (Gough et al., 2013)
Martino and colleagues (2002) showed that people who do not regularly exercise but are characterized by high-endurance performance, have a large volume of blood and a large amount of hemoglobin. This strongly suggests that a high amount of hemoglobin mass (Hbmass), which is required for excellent endurance performance, is predominantly genetically determined (landgraff and Hallen 2020). In various countries and athletic federations, Hbmass is, therefore, used as a powerful prognostic parameter in talent diagnostics. For example, Steiner et al. (2019) recently showed that Hbmass at age 16 is an important predictor for adult Hb-mass and the aptitude for high-level endurance performance. In a study conducted by Mancera et al. (2018), in 440 children and adolescents between 8 and 18 years of age, a difference in Hb-mass by more than 40% was shown within the individual age groups, which correlated closely with aerobic performance. The most important influencing factor on Hb-mass in male adolescents during and after puberty is blood testosterone level which raises Hb-mass levels to 40% higher values than in females (Mancera et al., 2019).
At altitude, the body adapts to the reduced oxygen supply by increasing the number of erythrocytes and the amount of hemoglobin mass (Hbmass). For example, residents at an altitude of 2600m show 7.5% and at 3600m 20% larger Hbmass values. When people ascend from the lowlands to altitude, it takes approximately one week for a true erythrocyte formation to be able to be observed. Maximum Hbmass values, like those found in high-altitude populations, are reached after about 6-8 weeks at the new altitude (Wachsmuth et al., 2013).
It is a well-known fact that athletes perform altitude training to prepare either for competitions at lowlands or, less often, for competitions at altitude. This can take place at real altitudes of mostly 1800m to 2500m or under comparable artificial hypoxic conditions Schmidt et al., 2020). With both methods, an increase in Hbmass of 1% is achieved after every 100 hours in hypoxia and a plateau value is reached after 4-6 weeks (Garvican et al., 2012). The hemoglobin expansion persists for at least three weeks and best performance is usually achieved during this time (Wachsmuth et al., 2013). Both established training methods, “Live high – train high” or “Live high – train low,” achieve the same success. However, some athletes do not benefit from altitude training measures and are known as non-responders.
Especially in endurance sports, many athletes try to improve their performance by using various types of blood manipulation such as erythropoietic stimulation or blood transfusions. Since autologous blood transfusions and certain erythropoietic manipulations cannot yet be detected, the World Anti-Doping Agency (WADA) introduced the Athlete Biological Passport (ABP) which includes a hematological module. Hemoglobin mass (Hbmass), which is the target parameter of every blood manipulation, should be permanently integrated into the passport (Prommer et al., 2008, Alexander et al., 2011). Screening an athlete’s Hbmass over time shows whether deviations in Hbmass are of biological or manipulative origin. This distinction is made possible using a Bayesian statistical model. In the event of a suspicious deviation, the athlete should be held accountable. Despite the very encouraging results of Hbmass tracking to date, WADA has not yet routinely introduced Hbmass measurement as part of the ABP.
The screening of Hbmass in professional athletes will enable anti-doping agencies to detect autologous or erythropoietic blood manipulations.
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