Response - Letter to the Editors

Dear Editors,

We thank Dr. Gore and Dr. Hahn for their interest in our study and in our results. Some of their comments are helpful, others have to be reconsidered. They are, for example absolutely right when saying that the inclusion of a control group would strengthen the scientific validity of our study. We agree that it is highly desirable to conduct controlled studies; however, as we were studying these athletes during their routine altitude training camp it was not possible to obtain V·O₂max tests under laboratory conditions. Furthermore, considering the fact that we worked with a highly selected group of world class athletes, it was impossible to find a matched control group with regards to endurance performance levels.

The mean increase of 9.3 % in total hemoglobin mass (tHb) found after a three-week conventional altitude training is in line with Levine and colleagues [[4]] who found an 8.7 % increase in athletes living and training high, and a 9.6 % increase in athletes living high - training low. As noted in our paper, prior studies which have found no significant effects for the most part have not been equivalent to ours in terms of conditions or subjects. Friedmann et al. [[3]] and Chapman et al. [[2]] found elevations of 6 % and 8 % in tHb-mass after three and four weeks altitude training, respectively. These values are slightly lower than ours. However, the difference is due to the characteristics of one athlete in our sample, who increased his tHb-mass by 18 %. Without his data, the mean increase is 7 %, and therefore within the range of other altitude studies. Consequently it is worthwhile to focus attention on this one athlete.

We agree with Drs. Gore and Hahn in their suggestion, that a leakage in the spirometer system leading to erroneous high tHb-values can never be completely excluded, although the probability of this is very low. Their second hypothesis, however, i.e. blood manipulation by this athlete, can be definitely rejected. Although evidence of erythropoietin (EPO)-doping has been found in other sports, such as cycling and cross-country skiing, there has been no evidence of such practices in biathlon. In addition, during the three weeks of altitude training all athletes were under the medical supervision of Dr. Heinicke and a variety of blood values were measured at five different times during that period without any indication for manipulations.

We are confident that the increase in tHb-mass of this athlete was due to individual physiological characteristics. Data relevant to this judgment are shown in Table [1]. This athlete's erythropoietic and oxygen status deviated markedly from that of the other athletes in this group: he showed a very large increase in hematocrit and EPO, large changes in soluble serum transferrin receptor (TFR), and a decrease in ferritin after arrival at altitude. However, he also manifested an immediate decrease in arterial hemoglobin oxygen saturation (SO₂) which was maintained for the duration of time at altitude. There are at least two explanations for such a low SO₂:

Table 1 Characteristics of erythropoietic activity and blood oxygen status of the athlete (A) with highest increase in tHb-mass and of the rest of the group (G) during a three-week altitude training Sea level Altitude day 1 day 4 day 20 tHb-mass (g) A G 1133 1117 ± 98 1340 1197 ± 131 Hct % A G 40.0 44.6 ± 1.0 40.5 45.8 ± 0.7 41.5 43.0 ± 2.1 46.0 46.9 ± 1.7 EPO (mU/ml) A G 6.6 12.8 ± 4.9 22.8 17.2 ± 4.4 14.2 22.1 ± 5.8 18.6 18.2 ± 5.7 TFR (nmol/l) A G 18.2 19.9 ± 2.1 16.9 21.3 ± 4.3 19.5 19.8 ± 2.1 21.6 21.7 ± 2.8 Ferritin (ng/ml) A G 117.3 105.3 ± 26.8 92.6 95.3 ± 24.9 79.1 93.4 ± 19.1 53.3 81.9 ± 19.3 SO2 (%) A G 95.4 95.1 ± 1.3 87.1 91.5 ± 0.6 87.8 89.3 ± 1.5 88.7 90.0 ± 1.1 P50 (mmHg) A G 29.2 27.8 ± 0.6 30.4 27.6 ± 0.6 31.8 27.0 ± 0.5 31.5 28.3 ± 1.0 tHb-mass = total hemoglobin mass, Hct = hematocrit, EPO = erythropoietin, TFR = soluble serum transferrin receptor, SO2 = oxygen saturation in arterialized blood, P50 = oxygen half saturation pressure

A low hypoxic ventilatory response (HVR) which is well known from polycythemic patients (Bernardi et al., [1]). Unfortunately, we did not determine HVR directly. However, the lower PO2 and the higher PCO2 in the blood of this athlete during the first days at altitude hint in this direction. The oxygen dissociation curve (ODC) of this athlete is clearly shifted to the right side (see table). Under resting conditions this may exert no significant negative effects. During exercise and training at altitude, however, a right shifted ODC may become disadvantageous (Schmidt et al. [5]). Already at an altitude of 1880 m, Sucec and Wicker [6] demonstrated a mean decrease in arterial SO2 during exercise from 87.9 % to 75.6 %, which is much more pronounced when the ODC is strongly shifted to the right side as in the athlete investigated in our study.

In conclusion, we agree with Dr. Gore and Dr. Hahn that the very large increase in tHb-mass in one of our athletes is extraordinary. But the analysis of his individual values (Table [1]) are proving an increased erythropoiesis which is most likely due to a higher individual degree of hypoxia in this athlete. In our opinion, he belongs to the group of high responders to hypoxia which are already described by Friedmann et al. [[3]] and Chapman et al. [[2]].

References

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• 2 Chapman R F, Stray-Gundersen J, Levine B D. Individual variation in response to altitude training.  J Appl Physiol. 1998;  85 1448-1456
• 3 Friedmann B, Frese F, Menold E, Kauper F, Jost J, Bärtsch P. Individual variation in erythropoietic response to altitude training in elite junior swimmers.  Br J Sports Med. 2005;  39 148-153
• 4 Levine B D, Stray-Gundersen J. “Living high - training low”: effect of moderate-altitude acclimatization with low-altitude training on performance.  J Appl Physiol. 1997;  83 102-112
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