The Effects of Hypobaric Hypoxia on Erythropoiesis, Maximal Oxygen Uptake and Energy Cost of Exercise Under Normoxia in Elite Biathletes

The aim of the present study was to evaluate the effects of 3 weeks altitude training according to the HiHiLo (live high-base train high-interval train low) procedure as described by Chapman et al. (1998), on erythropoiesis, maximal oxygen uptake and energy cost of exercise under normoxia in elite biathletes. Fifteen male elite biathletes randomly divided into an experimental (H) group (n = 7; age 27.1 ± 4.6 years; maximal oxygen uptake (VO2max) 66.9 ± 3.3 ml·kg–1·min–1; body height (BH) 1.81 ± 0.06 m; body mass (BM) 73.1 ± 5.4kg), and a control (C) group (n = 8; age 23.2 ± 0.9 years; VO2max 68.2 ± 4.1 ml·kg–1·min–1; BH 1.75 ± 0.03 m; BM 63.1 ± 1.5 kg) took part in the study. The H group stayed for 3 weeks at an altitude of 2015 m and performed endurance training on skis four times per week at 3000 m. Additionally, the training protocol included three high-intensity interval sessions at an altitude of 1000 m. The C group followed the same training protocol with skirollers in normoxia at an altitude of 600 m. The HiHiLo protocol applied in our study did not change VO2max or maximal workload (WRmax) significantly during the incremental treadmill test in group H. However, the energy cost for selected submaximal workloads in group H was significantly (p < 0.01) reduced compared to group C (-5.7%, -4.4%, -6% vs. -3.5%, -2.1%, -2.4%). Also a significant (p < 0.001) increase in serum EPO levels during the first two weeks of HiHiLo training at 2015 m was observed, associated with a significant (p < 0.05) increase in hemoglobin mass, number of erythrocytes, hematocrit value and percent of reticulocytes compared with initial values (by 6.4%, 5%, 4.6% and 16,6%, respectively). In group C, changes in these variables were not observed. These positive changes observed in our study led to a conclusion that the HiHiLo training method could improve endurance in normoxia, since most of the biathlon competitions are performed at submaximal intensities. Key points The observed results suggests that the 3-weeks HiHiLo protocol is an effective training means for improving energy cost during submaximal exercise at sea level. The 3-weeks HiHiLo protocol increased the rate of erythropoiesis and improved most haematological variables. However, the positive changes in the athletes haematological variables after the HiHiLo protocol did not contribute to the improvement of VO2max values. Key words: Altitude training, erythropoiesis, aerobic capacity, biathlon Introduction For the first time altitude training was applied in the training process almost fifty years ago. To make it more effective, its methodology has been constantly modified. As a result three concepts of high-altitude training have been accepted: live high-train high (LH-TH), live high-train low (LH-TL) and intermittent hypoxic training (IHT). Each of them combines the effects of acclimatization and different training procedures, what influences adaptation and performance (Levine and Stray-Gundersen, 1997; Wilber et al., 2007; Czuba et al., 2011). For example, the main factor limiting the effectiveness of the LH-TH concept is that many athletes cannot maintain high training intensity while staying at an altitude for a longer period of time and consequently decrease their level of endurance (Wilber et al., 2007). To overcome this problem Levine and Stray-Gundersen (1997) introduced the LH-TL method. This approach assumes that athletes should live at medium altitudes (2000-3000 m) in order to improve blood oxygen capacity, whereas training itself should be performed at an altitude not greater than 1200 m. This method allowed athletes to improve their blood oxygen capacity, while maintaining high training intensity (Wilber et al., 2007). Recently, significant attention in sport sciences has been given to IHT, which theoretically, may cause more pronounced adaptive changes in muscle tissues in comparison to traditional endurance training under normoxic conditions (Czuba et al., 2013). Improvement in sea-level performance and increased maximal oxygen uptake (VO2max) after IHT cannot be explained by changes in blood variables alone, but are also associated with non-hematological adaptive mechanisms (Czuba et al., 2011). Recently, Millet et al. (2010) introduced the possibility of combining different hypoxic training methods including intermittent hypoxic exposure at rest (IHE) during interval –training (IHIT) or LH-TL associated with IHT (LHTLH). Whereas reports on the impact of IHT on enchased glycolysis and buffering capacity (Gore at al., 2007), scientists have also discussed the potential benefits of this method for anaerobic performance. Therefore more recently, Millet at al. (2013) based predominantly on different mechanisms subdivided the IHT methods to: continuous low intensity ( 30 minut) exercise in hypoxia – CHT, interval training in hypoxia – IHT and repeated sprint training in hypoxia – RSH. The basic mechanism improving VO2max and thereby exercise capacity during both LH-TH and LH-TL training concepts is the stimulation of erythropoiesis, which results in increased blood oxygen capacity (Levine and Stray-Gundersen, 1997; Melissa et al., 1997). Another major factor improving exercise capacity after LH-TL training has been attributed to LL-TH-induced greater buffering capacity of muscle tissue (Gore et al., 2001) and/or to a decrease in exercise energy cost (Saunders et al., 2004a). The two mechanisms were also used to explain why exercise capacity increases after either LL-TH or IHT training, when its application did not lead to improved blood oxygen capacity (Czuba et al., 2011; Katayama et al., 2004; Rodriguez et al., 2004; Roels et al., 2005; 2007). However, there is a consensus in the literature that IHT training can improve exercise capacity by reducing exercise energy cost (Bonnetti et al., 2009; Czuba et al., 2011), increasing muscle tissue buffering capacity (Gore et al., 2001) and stimulating the activity of glycolytic enzymes (Katayama et al., 2004). Available data with regard to effects of altitude training on the energy cost of working muscles are unequivocal (Green et al., 2000; Gore et al., 2001; Levine and Stray-Gundersen, 1997; Svedenhag et al., 1991; Saltin et al. 1995). The LH-TL training has been found not to reduce the energy cost in normoxia (Levine and Stray-Gundersen, 1997; Telford et al., 1996), but in several studies (Gore et al., 2001; Katayama et al., 2003; Marconi et al., 2005; Neya et al., 2007; Saunders et al., 2004b; Schmidt et al. 2006) significant reductions in exercise energy cost after various procedures of altitude training were registered. Recently, Lundby et al. (2007) observed that submaximal VO2 is unchanged during and 2-3 days after chronic exposure from moderate altitude (2500-3000 m) up to altitudes of 4300 m. However, in the study of Schmitt et al. (2006) energy cost of exercise did not change immediately after LH-TL protocol but 15 days later was reduced in the non-specific activity. In specific activity this improvement was observed in both groups (LH-TL and control). The main reason of these discrepancies may be ascribed to different methodological approaches adopted by researchers, different sports level and genetic predispositions of subjects, as well as the level of hypoxia (altitude) and time of exposure (Chapman et al., 2014; Gore et al., 2013) Another significant factor to consider is the type of hypoxia used, because physiological adaptation to hypobaric vs. normobaric hypoxia is different, particularly with regard to lung fluid regulation (Millet et al., 2012). Bonetti and Hopkins (2009) reported in their meta-analysis that the LHTL protocol in natural conditions (hypobaric hypoxia) currently provides the best stimulus for enhancing endurance performance in elite and sub elite athletes, while some artificial protocols (normobaric hypoxia) are effective only in sub elite athletes. This may also explain why attempts at making the above methods more effective are being constantly made. One of the more interesting modifications in the LH-TL protocol was proposed by Chapman et al. (1998). According to the new solution, athletes should stay and perform low-intensity training at an altitude of 2500 m for four weeks, while high-intensity interval training should be performed at 1250 m. This method is known as HiHiLo (live high-base train high-interval train low). Stray-Gundersen et al. (2001) found a significant 3 % increase in VO2max accompanied by improvement of several hematological variables (hemoglobin mass and hematocrit) that resulted in significant improvement of running time (5.8 s, 3 km race) after the HiHiLo protocol. Therefore, one can assume that the HiHiLo protocol may be an effective training method, particularly applicable to cross-country skiers and biathletes during the preparatory period. Many winter sports athletes, in order to perform specific training on ice or snow during the preparatory period travel to the mountains and stay at high altitude. These procedures have been adopted by biathletes and cross-country skiers. The described above version of HiHiLo training is still not used frequently and reports on its effectiveness are limited. In particular, there are no data regarding the effects of HiHiLo training and a reduced energy cost of exercise in normoxia. Thus, we investigated if the HiHiLo procedure performed in hypobaric hypoxia conditions affects biathletes’ aerobic capacity and exercise energy cost in normoxia. Additionally, erythropoietin and selected hematological variables were evaluated, as potential factors influencing aerobic capacity and endurance performance.