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POINT-COUNTERPOINT COMMENTS

Comment on Point:Counterpoint "Positive effects of intermittent hypoxia (live high:train low) on exercise performance are/are not mediated primarily by augmented red cell volume"

Department of Physical Education
University of Las Palmas de Gran Canaria
Canary Islands, Spain; and
The Copenhagen Muscle Research Centre
Rigshospitalet
Copenhagen N, Denmark
e-mail: jcalbet{at}def.ulpgc.es

Robert Boushel

Department of Exercise Science
Concordia University
Montreal, Quebec, Canada

Carsten Lundby

Vetsuisse Faculty University of Zürich
Institute of Veterinary Physiology
Zürich, Switzerland

The following letter is in response to the Point:Counterpoint series "Positive effects of intermittent hypoxia (live high:train low) on exercise performance are/are not mediated primarily by augmented red cell volume" that appeared in the November 2005 issue (vol. 99: 2053–2058, 2005; http://jap.physiol.org/content/vol99/issue5).

To the Editor: Excellent discussion (5). However, the evidence for [Hb] changes as being the main factor accounting for the effects of altitude training on performance is weak, because the increase in [Hb] (5-10%) explained only 16% of the variance in the increase in O_{2 max}. In addition, the increase in O_{2 max} only minimally explained the variance of the improvement in performance. Moreover, the following facts deserve further attention. First, [Hb] increased by twice as much in the HiHi (live high:train high) than in the HiLo (live high:train low) groups, whereas the increase of O_{2 max} was similar in both groups. Second, it is not clear why the HiHi group did not improve performance despite the increase of O_{2 max} and [Hb]. Third, some subjects appear to improve their O_{2 max} more than accountable only by the increase in [Hb]. Fourth, blood transfusion studies show more marked effects on endurance (performance) than on O_{2 max} and report a reduction of submaximal exercise blood lactate concentration after transfusion. Altitude training appears not to have significant effects on submaximal blood lactate concentration (4). Fifth, isovolemic (1, 2) and hypervolemic (3) changes in [Hb] are consistently counterbalanced by changes in cardiac output and skeletal muscle blood flow such that for a given O₂ demand, O₂ delivery is maintained constant, but only during submaximal exercise. In Levine et al. (4), cardiac output was not affected by the increase of [Hb] when running at 8 and 10 mph (60 and 76% of their posttraining O_{2 max}), but it was reduced when running at 12 mph (90%). Thus the discussion remains open.

REFERENCES

1. Calbet JA. Oxygen tension and content in the regulation of limb blood flow. Acta Physiol Scand 168: 465–472, 2000.[CrossRef][Web of Science][Medline]
2. Calbet JA, Radegran G, Boushel R, Sondergaard H, Saltin B, and Wagner PD. Effect of blood haemoglobin concentration on O_{2 max} and cardiovascular function in lowlanders acclimatised to 5260 m. J Physiol 545: 715–728, 2002.[Abstract/Free Full Text]
3. Calbet JA, Radegran G, Boushel R, Sondergaard H, Saltin B, and Wagner PD. Plasma volume expansion does not increase maximal cardiac output or O_{2 max} in lowlanders acclimatized to altitude. Am J Physiol Heart Circ Physiol 287: H1214–H1224, 2004.[Abstract/Free Full Text]
4. Levine BD and Stray-Gundersen J. "Living high-training low": effect of moderate-altitude acclimatization with low-altitude training on performance. J Appl Physiol 83: 102–112, 1997.[Abstract/Free Full Text]
5. Levine BD and Stray-Gundersen J; Gore CJ and Hopkins WG. Point:Counterpoint: Positive effects of intermittent hypoxia (live high:train low) on exercise are/are not mediated primarily by augmented red cell volume. J Appl Physiol 99: 2053–2058, 2005.[Free Full Text]

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