1. Altitude and Hypoxic Training

Cycling is an endurance sport discipline in which the athlete encounters significant training and competition loads and is often exposed to extreme environmental conditions. Therefore, in cycling numerous performance-enhancing nutritional and physiological aids are used to improve the efficiency of the cardio-respiratory system. One of the legal and natural performance enhancing methods used in cycling includes altitude training, which significantly improves the cardio-respiratory potential.

2, 2max . Dempsey and Wagner [ 2 % below the 95% level approximates to a 1%–2% decrement in maximal oxygen uptake (VO 2max ). Diminished VO 2max in hypoxia is accompanied by a lowered O 2 partial pressure in arterial blood (PaO 2 ), which reduces O 2 delivery to tissues and negatively affects muscle metabolism and contraction [ The concept of altitude or hypoxic training is a common practice in cycling not only for improving sport performance at sea level but also at moderate altitude [ 1 3 ]. Cyclists often compete in races (e.g., Tour de France, Giro d ’Italia and Vuelta a España) at moderate altitudes (from 1000 to 3000 m a.s.l); what requires a specific adaptation to a hypoxia environment. At these conditions increasing altitude and the consequent reduction of air density is beneficial from the aerodynamic perspective [ 4 ], but on the other hand acute hypoxia deteriorates exercise performance [ 5 6 ]. In particular, the maximal aerobic workload that can be sustained during exercise involving large muscle groups (e.g., cycling) is considerably lower in hypoxia compared with normoxia. The origin of human performance limitation in hypoxia is attributed to a decrease in VO. Dempsey and Wagner [ 7 ] observed that each 1% decrement in SaO% below the 95% level approximates to a 1%–2% decrement in maximal oxygen uptake (VO). Diminished VOin hypoxia is accompanied by a lowered Opartial pressure in arterial blood (PaO), which reduces Odelivery to tissues and negatively affects muscle metabolism and contraction [ 8 9 ], leading to so-called peripheral fatigue.

10, After 40 years of altitude training, several strategies of such training regimens have been proposed, like “live high, train high” (LH-TH), “live high, train low” (LH-TL) or “intermittent hypoxic training” (IHT). Each of them combines the effect of acclimatization and different training protocols, which requires specific nutrition [ 3 11 ]. These nutrition concepts are due to different time of exposure to hypoxia at rest and different combinations of training under hypoxia and exposure to these conditions. In the LH-TH and LH-TL methods the acclimatization depends primarily on the iron status of the body, as well as on the maintenance of acid-base and energy equilibrium, what can significantly influence erythropoiesis. In the IHT method the dietary recommendations for athletes are less strict, and concentrate on pre-, mid- and post training unit nutrition. The specific demands of IHT relate to greater delivery of carbohydrates and better hydration.

2max ) and enhances physical performance [ 2 utilized [17, According to the first mentioned method, athletes live and train in a natural hypobaric hypoxic environment at moderate altitude for a few weeks. Chronic exposure to moderate altitudes (2000–3000 m) improves oxygen transport capacity by enhancing erythropoietin secretion and the consequential increase in total hemoglobin mass [ 12 13 ]. This adaptive change improves maximal oxygen uptake (VO) and enhances physical performance [ 14 ]. Chronic exposure to hypoxia may also reduce the energy cost of exercise at sea level by more efficient cellular metabolism [ 13 ]. The mechanism responsible for the decreased energy cost of exercise at sea level after altitude training is related to the increase of ATP production per molecule of Outilized [ 15 ], and/or a decreased ATP breakdown during muscular contractions [ 16 ]. These adaptive changes can be seen already after 3 to 4 weeks of exposure to moderate altitudes, but the main factor limiting the effectiveness of the LH-TH concept is that many athletes cannot maintain the required training intensity while staying at an altitude for a longer period of time, and consequently decrease their level of endurance and technical abilities [ 11 ]. In response to this weak point of LH-TH method, the LH-TL method was proposed by Levine and Stray-Gundersen [ 10 ]. The LH-TL protocol allows athletes to “live high (2000–3000 m)” for altitude acclimatization while “training low” (below 1000 m) for the purpose of replicating low-altitude training intensity and oxygen flux, thereby inducing beneficial metabolic and neuromuscular adaptations [ 11 ]. In this method athletes can live in a natural hypobaric environment, or use special technology based on nitrogen dilution or oxygen filtration, to simulate physiological adaptive changes by creating a normobaric hypoxia environment [ 17 18 ]. However, the current results of research on the efficacy of the LH-TL method are controversial. There are some studies which support the performance enhancing effects of LH-TL training on endurance performance and aerobic capacity [ 1 18 ], and those that do not confirm such effects [ 19 20 ].

2max after IHT cannot be explained by changes in blood variables alone, but is also associated with non-hematological adaptive mechanisms [ Recently, significant attention in sport sciences, as well as in competitive cycling has been given to IHT, which theoretically, may cause more pronounced adaptive changes in muscle tissues in comparison to traditional training under normoxic conditions [ 21 ]. In this method, athletes live under normoxic conditions and train in a natural hypobaric or simulated normobaric hypoxic environment. The improvement in sea-level performance and an increase in VOafter IHT cannot be explained by changes in blood variables alone, but is also associated with non-hematological adaptive mechanisms [ 3 ]. The results of our previous studies [ 3 13 ] and other well-controlled studies [ 22 23 ] indicate that the improvements in aerobic capacity and endurance performance are caused by muscular and systemic adaptations, which are either absent or less developed after training under normoxia. These changes include increased skeletal muscle mitochondrial density, elevated capillary-to-fiber ratio, and increased fiber cross-sectional area [ 24 25 ].

27,28, Acute and chronic exposure to hypoxia induces serval metabolic consequences in the body and combined with physical exercise under hypoxic conditions presents an enormous challenge for athletes [ 26 29 ]. A significantly lower oxygen concentration in the blood, forces the body to produce the energy primarily from other substrates than in normoxia [ 30 ]. The athlete’s body needs 2–3 weeks to adapt to the low level of oxygen, or else they feel fatigue, headaches and a decrease in appetite [ 31 ]. An appropriate nutrition strategy can help athletes achieve their fitness and performance goals in this unfriendly environment.