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Nutrition and Performance in Sport

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Christophe Hausswirth

Chapter 1. Nutrition: from training to competition

Topic 4. Nutritional needs for training at mid-range altitude

Charles-Yannick Guezennec et Fabienne Durand

Résumé

While training at mid-range altitude, it is essential to adapt nutrition to gain maximum benefits. The nutritional adaptation should follow two principles: firstly, it should respect the standard diet for an athlete (depending on the type of sport and age) and, secondly, it should allow for specific dietary needs defined by training at mid-range altitude.
It is now well established that intense physical activity at altitude can modify body composition. This phenomenon mainly leads to a decrease in muscle mass, but also reduces fat mass. Reduced mass is almost always seen with prolonged exposure to altitudes higher than 3000 m. Particularly intense or prolonged physical trainings can decrease the weight-loss threshold at altitudes between 1800 and 2000 m, and most training centres for Olympic disciplines are located at these altitudes.
The first measure to adopt to match food intake to the needs of athletes training at these altitudes is to regularly measure changes to their body composition.
One of the mechanisms behind the weight loss observed is modified eating behaviour: appetite is reduced at altitude, especially after intense training sessions. This phenomenon can deteriorate the quality of recovery. In fact, sporting success at altitude is closely linked to the subjects’nutritional status. To allow good recovery, it is thus necessary to provide athletes with food which helps combat appetite reduction through taste and composition.
In addition to effects on appetite, training at altitude can increase common respiratory tract infections in athletes with an intense level of activity. Nevertheless, it was shown that this disadvantage could be prevented by increasing calorie intake and systematically consuming carbohydrates during the recovery phase.
Altitude, in itself, can also deteriorate sleep quality, leading, very often, to a decrease in the positive effect of this kind of training. The timing and make-up of meals should be adapted to facilitate going to sleep.

Texte intégral

1. Training at altitude

1Since the Mexico Olympic Games (1968), many studies have investigated training at mid-range altitude. Although some conclusions are indisputable, others are more controversial.

2To clarify the debate, we must start with initial hypotheses relying on the well-known physiological effects of adaptation to mid-range altitude. Thus, it is well established that all the systems of oxygen transport (from ambient air to muscle cell) adapt to increase the oxygen supply to the various tissues. This is necessary as altitude is associated with several modifications of the physical characteristics of the environment. The main modification is a progressive decrease in barometric pressure, which leads to a decrease in the partial pressure of oxygen in the air. While the percentage of oxygen in inhaled air remains constant (about 21%), the partial pressure of oxygen decreases through the effects of the same law that regulates barometric pressure.

Figure 1: Evolution of blood O2 saturation during a maximal event performed at sea level and at 1850 m above sea level by triathletes.

Figure 1: Evolution of blood O2 saturation during a maximal event performed at sea level and at 1850 m above sea level by triathletes.

*: significant difference between the two conditions (P<0.05);
**: significant difference compared to rest in the same condition (P<0.01);
***: significant difference compared to rest in the same condition (P<0.001);
****: significant difference between the two conditions (P<0.05).
Adapted from Durand and Estripeau (2011).

3Because of this, the physiological effects of altitude are similar to those of hypoxia, and this correlates with the duration of exposure. One of the easiest parameters to measure, and which allows the level of hypoxia experienced by the body to be assessed, is arterial oxyhaemoglobin saturation (SaO2). The reaction to hypoxia provokes mechanisms that tend to limit the reduction of oxygen supply to tissues. In the short term, the body will react quickly, increasing the respiratory and cardiac output, to increase oxygen supply to tissues. But, despite these rapid reactions, the decrease in oxygen availability at altitude will lead to a decrease in maximal oxygen consumption. Theoretical data indicates that the VO2 max decreases from an altitude of 1500 m. Beyond this threshold, it further decreases by 2 to 3% for every additional 300 m elevation (Terrados et al. 1992). In highly trained endurance athletes, the decrease in VO2 max is perceptible from an altitude of 600 m (Gore et al. 1996), and some athletes, those with a particularly high VO2 max, even present arterial oxygen desaturation during maximal effort at sea level. This phenomenon is known as exercise-induced arterial hypoxaemia (EIAH). In these athletes, the fall-off in VO2 max is higher at altitude, because the environment in these conditions appears to maximize EIAH (Durand and Estripeau, 2011) [Fig. 1]. As a consequence, as soon as athletes are exposed to the altitude of the training centre, generally greater than 2000 m, their aerobic capacities become limited. This limitation must be taken into account when planning training. However, prolonged exposure to altitude induces adaptation phenomena in the long term that modify some of the body’s structural properties, enhancing oxygen transport and use.

2. Advantages of training at altitude

4These elements, which were discovered in the 1970s, led many to suppose that adaptations to altitude could increase aerobic capacities at altitude (or upon return to sea level). However, it is now well established that one must live and train at altitude to perform well at altitude. The other potential application is to enhance performance at sea level after a training course at altitude. The hypothesis of an increase in VO2 max after a training course at altitude relies mainly on the fact that this type of preparation is likely to enhance the O2 transport capacity in the blood and the metabolic adaptations occurring in the muscle to deal with reduced O2 availability. This hypothesis has been extensively studied, but the results have often been contradictory (De Paula and Niebauer, 2010), with significant variations from one athlete to another. However, it was shown that training at altitude could help to improve short-term maximal performance. This result is partly due to enhanced muscle hypertrophy induced by resistance training in a hypoxic environment (Nishimura et al. 2010), and partly to improved muscle metabolic recovery after short-term maximal exercise (Bishop et al. 2013). These physiological adaptations sustain the recent finding that the capacity to repeat sprints increases after altitude training (Galvin et al. 2013). Nevertheless, the benefits of altitude training on performance are subject to extensive inter-individual variability, as reviewed by Mazzeo (2008); Chapman et al. (1998) introduced the concept of “responders” and “non-responders” to altitude. Thus, training at altitude is beneficial for some athletes, whereas it is not efficient, or even causes problems, for others. Among the various factors that could explain this variability, nutrition plays a key role. Adequate dietary intake could optimize oxygen convection and peripheral use through effects on haemoglobin mass and muscle metabolism, it is also critical for the muscle’s response to resistance training by providing substrate for optimal muscle protein synthesis. Although many studies have been carried out to attempt to determine nutritional needs during expeditions at high altitude, the needs of Olympic athletes training at mid-range altitude, have been the subject of much less work. Because of this, we often have to extrapolate from data obtained at higher altitudes when seeking to establish recommendations about training at mid-range altitude. There are arguments to support this data transfer from one situation to the other: for high effort intensities, the level of desaturation at mid-range altitude is greater in athletes than in sedentary populations (Woorons et al. 2005). This observation backs up the idea that intense training at about 2000 m can produce oxygen desaturation in these subjects and the metabolic consequences normally observed at a higher altitude. When training at altitude is specifically adapted for athletes who experience EIAH at sea level, the adaptations are even greater. In effect, as mentioned, the amplitude of oxygen desaturation at altitude is maximized by the environment, making the physiological constraints comparable to those experienced at high altitude, even if the athlete is at mid-range altitude (Durand and Estripeau, 2011).

3. Blood adaptations

5The first phenomenon noted upon exposure to altitude is an increase in erythrocyte and haemoglobin concentration. This increase is rapid during the first days, and then slows. These changes can continue for several months, or even years (Berglund, 1992). The variations in the number of red blood cells and haemoglobin are more prominent at higher altitudes, but inter-individual variability is also noted. Living and training for three to four weeks at between 2000 and 3000 m above sea level has been shown to improve haemoglobin mass by more than 6% in Olympic swimmers (Bonne et al. 2014). Exposure to hypoxia increases iron absorption from the diet to stimulate erythropoiesis. This mechanism is controlled by hepcidin, a central regulator of iron metabolism, which decreases intestinal iron absorption. Hypoxia reduces hepcidin expression to enhance circulating iron availability (Hintze et al. 2011). This phenomenon could result in a negative iron balance if the dietary iron supply is not increased before and during training at altitude. Altitude polycythaemia is a consequence of erythropoietin hyperactivity due to increased erythropoietin secretion. Erythropoiesis is only stimulated by exposure to an altitude greater than 1600 or 1800 m. Polycythaemia linked to a prolonged stay at altitude presents an advantage, insofar as it enhances oxygen transport both at altitude and when the athlete returns to sea level. Part of the difference between good and bad “reactions” to training at altitude appears to be due to the individual’s capacity to increase their red blood cell mass (Chapman et al. 1998). McLean et al. (2013) recently established a year-to-year individual difference in haemoglobin mass response to altitude training. These authors conclude that the response to altitude training is not a fixed trait, and that nutritional intake plays an essential role in this adaptation. Stray-Gundersen (1992) showed that iron deficiency, before a training course at altitude, prevented the stimulation of erythropoiesis. In contrast, “good reactors” – those whose performances increased during the course at altitude – were those who had a good level of iron storage. It is thus proven that iron availability is necessary to increase the total red blood cell mass in response to training at altitude. However, the increase in red blood cells can be a disadvantage, as it increases blood viscosity, this phenomenon is reinforced by the decrease in red blood cell deformability at altitude. Oxygen availability also modifies erythrocyte metabolism, mainly in terms of carbohydrate metabolism, making erythrocyte membranes more rigid. This increase in viscosity and rigidity of red blood cells results in an increase in vascular resistance, which creates more work for the heart. Two nutritional measures can limit the deleterious consequences of these phenomena on performance:

  • hydration, which should be kept high to increase the plasma volume;

  • the intake of polyunsaturated fatty acids, which make red blood cell membranes more fluid; this nutritional measure was shown to help for exercises performed in conditions of intermittent hypoxia at 3,000 m (Guezennec et al. 1989) [Fig. 2].

Figure 2: Variations of erythrocyte filtration index in individuals taking polyunsaturated fatty acid (PUFA) supplements, before or after 1 hour of exercise performed in normoxia or hypoxia (at 3000 m). Values shown are averages (± standard deviation).

Figure 2: Variations of erythrocyte filtration index in individuals taking polyunsaturated fatty acid (PUFA) supplements, before or after 1 hour of exercise performed in normoxia or hypoxia (at 3000 m). Values shown are averages (± standard deviation).

*: significant difference compared to values measured in normoxia (P<0.05). Adapted from Guézennec et al. (1989).

6Many studies have shown a link between saturated and unsaturated fatty acids in various cell membranes and the fluidity of these membranes. It is thus possible to reduce the deleterious consequences of hypoxia on blood rheology by modulating unsaturated lipid intake.

4. Metabolic and muscle tissue adaptations

4.1 Adaptations to energy metabolism and effects on body composition

7The metabolic demands of life and exercise are progressively increased by rising altitude level. The resting metabolic rate is increased by hypoxia, while intense physical activity at altitude requires more energy than the same physical workload at sea level. However, it is well known that exposure to high altitude reduces appetite, which could result in an energy imbalance (Hill et al. 2011). The main consequence of exposure to altitude is thus weight loss, as illustrated by the results of the American medical expedition to Everest in 1981 (Blume et al. 1984). This study reported that the climbers, all of whom were born at low altitude, lost an average of 2 kg during the approach (from 1000 m of altitude to the base camp located at 5400 m). Three main causes were implicated: decreased food intake resulting from altitude-induced anorexia, and increased basal metabolic rate and dehydration (Macdonald et al. 2009). A 35 to 40% decrease in food intake was recorded during stays at high altitude as part of expeditions in the Himalayas, from altitudes greater than 5000 m (Westerterp-Plantenga et al. 1999) [Fig. 3]. Thus, food intake regulation appears to be the main contributor to body composition changes under the effects of training at altitude. In support of this conclusion, many studies show that leptin levels increase upon exposure to high altitude (Grosfeld et al. 2002). This hormone plays an important role in regulating food intake by inducing a feeling of satiety. The raised levels recorded were suggested to be a potential explanation for reduced food consumption at altitude.

8Other peptides regulating hunger sensations (such as glucagon-like peptide [GLP], adiponectin and ghrelin) have also been suggested to regulate energy intake at high altitude (Snyder et al. 2008), but their precise roles remain to be determined. A study performed on the population participating in a mountaineering race lasting two days, between 2400 m and 3600 m, sought to identify the altitude threshold from which eating behaviour is affected. The data relating to food behaviour after the trail shows a decrease in sensations of hunger, with an increase in satiation and in the feeling of a full stomach at 3600 m. These parameters do not appear to be affected at 2400 m (Bourrilhon, 2009). Therefore, eating behaviour should not be modified during a training course at mid-range altitude. However, there may be an interaction between tolerance to intense training at mid-range altitude and eating behaviour. It is generally admitted that spontaneous reduction of food intake is one of the early warning signs of overtraining and of intolerance to an excessive level of training (Fry et al. 1991). If we consider the fact that intense training at mid-range altitude can increase the risk of intolerance to training, it is possible that this kind of training favours an energy imbalance. The effects of intense training at mid-range altitude on body composition were recently shown in swimmers to include loss of fat mass and a slight increase in lean mass, without changes to body weight, after three weeks of training at 2300 m (Chia et al. 2013). These data could be discussed in the light of several recent studies conducted on obese subjects, as reviewed by Kayser et al. (2013). The increased basal metabolic rate as well as training at altitude can trigger an energy imbalance by increasing ventilatory flow and cardiac output in response to hypoxia (Green et al. 1993). The combination of these adaptations and the reaction to hypoxia underlines the need to increase food intake to balance the increased energy expenditure during training at altitude (Fig. 3).

Figure 3: Variations of erythrocyte filtration index in individuals taking polyunsaturated fatty acid (PUFA) supplements, before or after 1 hour of exercise performed in normoxia or hypoxia (at 3000 m). Values shown are averages (± standard deviation).

Figure 3: Variations of erythrocyte filtration index in individuals taking polyunsaturated fatty acid (PUFA) supplements, before or after 1 hour of exercise performed in normoxia or hypoxia (at 3000 m). Values shown are averages (± standard deviation).

*: significantly different from the values measured before the period spent in a hypobaric chamber, for the total energy intake (P<0.01).
**: significantly different from the values measured before the period spent in a hypobaric chamber, for energy intake during each meal (P<0.01).
Adapted from Westerterp-Plantenga et al. (1999).

9How metabolic pathways adapt to the effects of altitude is an area of ongoing discussion. Young et al. (1982) suggested that adaptation to high altitude was accompanied by an increased use of lipid substrates, resulting in glycogen sparing during prolonged effort at altitude. Later, Brooks (1991) suggested the opposite: acclimatization for three weeks at 4300 m increases the use of glucose during submaximal exercise of the same absolute intensity as at sea level. Further studies by McClelland (1998) showed that the contribution of carbohydrate metabolism was similar at sea level and at altitude, if metabolism was studied at an equivalent level of physical activity (determined based on the reduced oxygen consumption generated by hypoxia). Van Hall et al. (2002) showed a similar consumption of carbohydrates, but an increased oxidation of lactate for the same absolute workload at 5600 m (compared to sea level), which globally corresponds to an increase in the glycolytic contribution to metabolism. More recently, Katayama et al. (2010) showed that submaximal activity of the same relative intensity as at sea level, but performed during exposure without preliminary adaptation to hypoxia simulating an altitude of 2000 m, increased the use of carbohydrates. The source of this debate on metabolic orientations at altitude can be found in the data obtained on muscle enzymatic adaptations. Thus, adaptation to altitude continually increases the expression and activity of glycolytic enzymes in the muscle (Voigt and Hoppeler, 2010). This phenomenon appears to be mainly stimulated by the reaction of the transcription factor Hypoxia-Inducible Factor (HIF) during physical training at altitude (Hoppeler et al. 2003). The muscle’s glycogen consumption is facilitated by activation of a marker of the muscle’s metabolic status: AMP-activated protein kinase (AMPK). During exposure to altitude, the increase in AMPK activity stimulates the transport of blood glucose toward the muscle (Wadley et al. 2006). It is also well established that hypoxic training improves insulin sensitivity, as reviewed by Chen et al. (2013). It is thus reasonable to suppose that training at mid-range altitude is accompanied by an increased use of carbohydrates. This phenomenon presents a metabolic advantage because it produces a higher proportion of ATP molecules per mole of glucose metabolized (Hochachka et al. 1991). This increase in the use of carbohydrate substrates, accompanied by a concomitant reduction in the use of lipid substrates, was also shown at the level of the myocardium upon exposure to severe hypoxia. This model is interesting if we consider its consequences. Indeed, the myocardium is a contractile system which generally uses lipids as energy substrates, but severe hypoxia forces it to draw on the normally spared glycogen stores (available in case of urgent metabolic needs) [Guezennec et al. 1989]. Logically, this increase in the contribution of carbohydrates to total energy metabolism leads to a decrease in the lipid contribution (Roberts et al. 1996). Depletion of glycogen stores may thus be faster at altitude (Hochachka et al. 1991), and consequently carbohydrate requirements increase during training at mid-range altitude (particularly during the recovery phase), if glycogen stores are to be maintained.

4.2 Muscle adaptations

10It is now well established that all structural and metabolic adaptations depend on the same regulating factor, Hypoxia-Inducible Factor (HIF), a transcription factor which is considered to be a tissue oxygenation sensor (Semenza, 2004) regulating the expression of genes coding for muscle structures and metabolic functions. At the muscle level, where most oxygen is used during an effort, several structural adaptations occur depending on the duration and intensity of exposure to altitude. These adaptations lead to an increase in the number of mitochondria and in the density of the perimuscular capillary network, which favours oxygen supply and extraction (Flueck, 2010). When exposure to high altitude is prolonged, there is a decrease in the surface of muscle fibres, which enhances oxygen diffusion toward the muscle’s metabolic machinery. This improvement in oxygen supply to the muscle’s metabolic machinery is associated with a major disadvantage for athletes: a decrease in muscle strength. Lean mass reduction, which is observed during expeditions at high altitude, is one of the factors that limits this drop in strength. In addition, exposure to high altitude causes the nitrogen balance to become negative, even when food intake is not restricted. Because the metabolic orientation results from effective deterioration of muscle proteins (Chaudhary et al. 2012) we will discuss this effect further below. Muscle wasting is well documented during prolonged exposure to high altitude. A chronic imbalance in the levels of proteins synthesized or degraded influences the muscle mass. Altitude could cause muscle wasting by altering both muscle protein synthesis and degradation (Wing-Gaia, 2014). An overall analysis of protein synthesis pathways using proteomic techniques reveals that all the processes leading to muscle protein synthesis are reduced during exposure to altitudes greater than 4000 m (Flueck, 2009). Muscle protein breakdown is mainly regulated through the ubiquitin proteasome (UP), lysosomal, and calpain systems. From a cellular perspective, the mammalian target of rapamycin (mTOR) pathway is a central point of control for muscle protein synthesis as it occupies a central point of convergence for nutritional and contractile anabolic signals (Chaudary et al. 2012; Wing-Gaia et al. 2014). In an attempt to control these pathways, many authors have attempted to define optimum protein intake in this type of situation. A study performed on an animal model exposed to high altitude did not confirm that a high protein intake helps to preserve muscle mass (Bigard et al. 1996b), but two studies performed during ski trails, at altitudes between 2000 and 3500 m showed that intense physical exercise lasting several days, at mid-range altitude, caused a decrease in the plasma concentration of branched-chain amino acids (Bigard et al. 1993, 1996a). Given the role played by these amino acids – and of leucine in particular – in protein syntheses, it seems likely that increasing the intake of this type of nutrients could help to preserve muscle mass during periods of physical activity at altitude. Currently, the experimental data are inconclusive: one study, performed during a trek at high altitude, shows that a significant intake of branchedchain amino acids can minimize muscle mass reduction (Schena et al. 1993), whereas a more recent study conducted during a trek at a mean altitude of 4140 m (Wing-Gaia et al. 2014) indicated that extensive leucine supplementation does not reduce the drop in lean mass.

4.3 Exposure to altitude and production of free radicals

11It is known that training at altitude accelerates the appearance of oxygen-derived reactive species, known as free radicals (Pialoux et al. 2006, 2010). The presence of a single electron makes these molecules highly unstable, which means that they can react with various elements in the body. Because of their potential toxicity (due to reaction with the cell membrane, affecting the integrity of the genetic message contained in DNA, or having an impact on the endothelial walls in blood vessels), these free radicals are potentially responsible for some of the negative effects of intense physical exercise, such as muscle membrane lesions. At altitude, even though oxygen flux is reduced, the production of free radicals increases (Pialoux et al. 2006). This increase is linked to the fact that, at altitude, there are fewer oxygen molecules available to accept the free electrons produced by free radical reactions. It must be remembered that the defence against an excess of free radical production relies on an antioxidant system, which can be either active or passive. The active system is based on enzymes (such as catalase, glutathione peroxidase [GPx] and superoxide dismutase [SOD]) that neutralize free radicals by binding to them. The body can also use non-enzymatic antioxidants to prevent the formation of free radicals. Many of these antioxidants are found in our food, they include: vitamin A, vitamin C, vitamin E, vitamin B6, zinc and selenium. Given the increased risk of lipid peroxidation, it is essential to combat the formation of reactive oxygen species in humans training at altitude. During an experiment combining life at altitude and training at a lower level, researchers showed a decrease in plasma concentrations of vitamins E and A, associated with an increase in oxidative stress indicators (Pialoux et al. 2010). According to these authors, this change can be explained by a deficiency in antioxidant vitamins. This led to a hypothesis whereby the consequences of oxidative stress generated by altitude exposure could be minimized by vitamin E supplementation (Simon-Schnass, 1992). In the conditions of a Himalayan expedition, vitamin E supplementation limited the specific effects of chronic hypoxia on the hydrocarbon concentration in exhaled gases, which is an indicator of the level of peroxidation of membrane structures. Although this study did not show any effect on physical performance, a previous study (Subhudy et al. 2006) showed an improved power output at the ventilatory threshold during incremental exercise performed at altitude after prolonged antioxidant supplementation. Other data (Gatterer et al. 2013) reveal that short-term antioxidant supplementation does not prevent the drop in performance noted at altitude, but does have a positive effect on oxygen extraction.

5. Effects of altitude on hydration

12Another important factor in weight loss is possible dehydration during training at altitude. Dehydration may occur as water losses are increased due to the physical environment experienced at altitude: the dry air favours losses through perspiration and evaporation from the skin. Thus, water loss contributes to weight reduction and particularly to the decrease in performance. It is well established that dehydration at sea level reduces aerobic performances in proportion to the extent of water loss, but the question is whether altitude exposure and decreased hydration have a cumulative effect on the decrease in aerobic capacity. This question was recently answered by Castellani et al. (2010). These authors compared performance levels during a maximal aerobic “Time Trial” type exercise performed in a hypobaric chamber, at a simulated altitude of 3000 m, in a dehydrated or well-hydrated population. Dehydration resulting in a 4% decrease in body weight was obtained by combining prolonged exercise with water restriction; these conditions reproduced the dehydration mechanisms experienced during physical activity at altitude. The results showed a 34% decrease in performance in dehydrated subjects at altitude, whereas for well-hydrated subjects the decrease in performance was only 11%. There is thus a cumulative effect of dehydration and hypoxia on aerobic capacity. These results lead us to suppose that even a minimal reduction of the hydration level of athletes during training at altitude can have a significant impact on the capacity to maintain a submaximal fraction of O2 consumption.

6. What practical advice can be given for nutrition while training at mid-range altitude?

6.1 Increase food intake

13Because overall energy expenditure increases at altitude, it is necessary to increase the daily calorie intake from the beginning of a training course at altitude, even if the level of energy expenditure due to training remains unchanged. The balance between energy intake and expenditure can be monitored by regularly checking the weight curve, and by a less frequent measurement of fat mass using a Harpenden skinfold caliper. As mentioned above, the spontaneous reduction of food intake at altitude is mostly linked to direct effects of hypoxia on biological mechanisms controlling food intake. In the absence of published results on the effects of intense training at mid-range altitude on food behaviour, we can hypothesize that the high levels of blood O2 desaturation experienced can induce similar effects to high altitude on eating behaviour (if athletes are sensitive to EIAH, or during particularly intense training sessions). As it has already been shown that intense training at sea level has a short-lived anorexic effect (Verger et al. 1994), it is possible that intense training at altitude has a cumulative effect on appetite reduction. Therefore, eating behaviour must be monitored during training courses at altitude, particularly as an imbalance between energy intake and expenditure is considered one of the essential factors predisposing to overtraining (Guezennec, 2004). One of the primary ways of limiting this impact is to favour spontaneous food consumption by enhancing the quality of meals and the organoleptic properties of food.

6.2 Increase carbohydrate intake

14We have said that the main metabolic modification resulting from life at altitude is an increased use of carbohydrates. It is thus absolutely necessary to increase the contribution of carbohydrates to the total energy intake (TEI). This proportion should already be greater than 50% of the TEI in a normal training situation, but during a course at altitude, an intake corresponding to about 55 to 60% of the TEI appears optimal. A recent publication showed that elite Ethiopian runners who train at 2400 m consumed about 65% of their TEI in the form of carbohydrates (Beis et al. 2011). To achieve this intake, training sessions should be preceded by, or include, intake of a portion of carbohydrates (depending on duration), and even more importantly, carbohydrates should be eaten immediately after the effort, during the recovery phase. Another major advantage to increasing carbohydrate intake lies in the clinically proven increase in the frequency of respiratory tract infections during training at altitude. According to studies by Nieman et al. (2006), the most efficient way to prevent this type of infection consists in increasing carbohydrate intake, particularly just after exercise.

6.3 Favour nitrogen intake

15At mid-range altitude, unlike at high altitude, there is no evidence of an effect on the nitrogen balance. However, it is important to ensure that the recommendations established for intense training at low altitude are respected: about 1.6 g.kg.d–1 of protein for sports with a high energy expenditure, about 2 g.kg.d–1 for disciplines in which muscle mass must be developed. During training courses at mid-range altitude, it seems more useful to favour the nature and timing of the protein portion rather than its size. Since iron status has a significant impact on the quality of the reaction to training at altitude, for reasons of bioavailability, it is useful to favour haematinic iron intake by eating meat (mainly red meat) at the main meals. Finally, several studies highlight the advantages of consuming milk-derived proteins, especially during the recovery phase. Milk-derived proteins optimize protein synthesis during this phase (Wilkinson et al. 2007). Therefore, it seems important to consume foods containing both protein and carbohydrate during recovery, because these nutrients have a synergistic effect on protein synthesis and the replenishment of glycogen storage (Levenhagen et al. 2002).

6.4 Increase water intake

16Exercise at altitude represents a high-risk situation for the hydroelectrolyte balance. Indeed, insensible water loss from the respiratory tract is increased, and cold air – which is frequent at mid-range altitude – stimulates diuresis. In addition, this water loss is not directly perceived by the subject, which increases the risk of dehydration. Given the consequences of dehydration on performance, as shown by Castellani et al. (2010), athletes must make sure that they drink a lot, and regularly. In temperate climatic conditions, it is recommended to increase water intake by 1.5 litres over what is usually consumed at lower altitude (Millet and Schmitt, 2011). In practice, regular weighing can be used to detect the onset of dehydration. Another – somewhat more complex – method can also be used by the medical entourage: urine colorimetry (Armstrong et al. 1998).

6.5 Combat the production of oxygen free radical species

17We saw previously that physical activity at altitude could increase free radical production. Many recent studies have shown that taking high levels of vitamin supplements does not have an ergogenic effect, and that if taken over a prolonged period, these supplements are likely to have toxic effects. Given these potential disadvantages, it is recommended to increase the body’s antiradical capacities by consuming foods rich in antioxidants (such as juice, fruit, vegetables, brewer’s yeast and wheat germ). These foods are particularly useful during recovery.

6.6 Haemorheology and polyunsaturated fatty acid supplementation

18Prolonged hypoxia leads to a decrease in red blood cell deformability, which hampers their penetration into muscle capillaries. It was hypothesized that supplementing the diet with polyunsaturated fatty acids, which are known to increase membrane deformability, could minimize the negative effects of altitude on aerobic performance. The most efficient way to do this consists in increasing consumption of fish and shellfish, particularly oily fish (such as mackerel), before and during the training course at altitude. In addition, most vegetable oils are rich in unsaturated fatty acids, especially rapeseed, maize and olive oil.

7. Conclusion

19Training at mid-range altitude has been the subject of renewed interest in the light of recent publications highlighting its positive effects, its limitations and the conditions to be respected to optimize its efficiency. Among the conditions necessary to derive performance benefits from this kind of training, nutrition is one of the most important.

20Indeed, the nutritional plan to optimize the effects of a training course at altitude must start before exposure to hypoxia. This early start will increase the body’s stores of essential elements (necessary to tolerate the training and to performance), including iron and antioxidants. Some essential principles must also be applied from arrival at altitude, such as increasing hydration and carbohydrate intake.

21The importance of the role played by nutrition justifies an individual nutritional check-up at the beginning of the training course to detect any deficiencies early and to offer a diet corresponding to individual needs and tastes.

22Even more than at sea level, the food offered to athletes training intensely at mid-range altitude must be tasty and well presented. This will make it easier for the athlete to eat enough and to vary their food intake.

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