Role of Maximal Heart Rate and Arterial O₂ Saturation on the Decrement of V·O_2max in Moderate Acute Hypoxia in Trained and Untrained Men

Abstract

We aimed to evaluate 1) the altitude where maximal heart rate (HR_max) decreases significantly in both trained and untrained subjects in moderate acute hypoxia, and 2) if the HR_max decrease could partly explain the drop of V·O_2max. Seventeen healthy males, nine trained endurance athletes (TS) and eight untrained individuals (US) were studied. Subjects performed incremental exercise tests at sea level and at 5 simulated altitudes (1000, 1500, 2500, 3500, 4500 meters). Power output (PO), heart rate (HR), arterial oxygen saturation (SaO₂), oxygen uptake (V·O₂), arterialized blood pH and lactate were measured. Both groups showed a progressive reduction in V·O_2max. The decrement in HR_max (ΔHR_max) was significant from 1000 m for TS and 2500 m for US and more important in TS than US (at 1500 m and 3500 m). At maximal exercise, TS had a greater reduction in SaO₂ (ΔSaO₂) at each altitude. ΔHR_max observed in TS was correlated with ΔSaO₂. When the two groups were pooled, simple regressions showed that ΔV·O_2max was correlated with both ΔSaO₂ and ΔHR_max. However, a multiple regression analysis demonstrated that ΔSaO₂ alone may account for ΔV·O_2max. Furthermore, in spite of a greater reduction in SaO₂ and HR_max in TS, no difference was evidenced in relative ΔV·O_2max between groups. Thus, in moderate acute hypoxia, the reduction in SaO₂ is the primary factor to explain the drop of V·O_2max in trained and untrained subjects.

Key words

Arterial oxygen content - altitude - performance - athletes

References

• 1 Benoit H, Busso T, Castells J, Devis C, Geyssant A. Influence of hypoxic ventilatory response on arterial O₂ saturation during maximal exercise in acute hypoxia.  Eur J Appl Physiol. 1995;  72 101-105
• 2 Benoit H, Busso T, Castells J, Geyssant A, Denis C. Decrease in peak heart rate with acute hypoxia in relation to sea level V·O_2max.  Eur J Appl Physiol. 2003;  90 514-519
• 3 Calbet J AL, Boushel R, Radegran G, Sodergaard H, Wagner P D, Saltin B. Determinant of maximal oxygen uptake in severe acute hypoxia.  Am J Appl Physiol. 2003;  284 R291-R303
• 4 Cerretelli P, Bordoni U, Debijadij R, Saracino F. Respiratory and circulatory factors affecting the maximal aerobic power in hypoxia.  Archivio di fisiologia. 1967;  vol. LXV 344-357
• 5 Chapman R F, Emery M, Stager J M. Degree of arterial desaturation in normoxia influences V·O_2max decline in mild hypoxia.  Med Sci Sports Exerc. 1999;  31 658-663
• 6 Dempsey J A, Hanson P G, Pegelow D, Claremont A, Rankin J. Limitations to exercise capacity and endurance: pulmonary system.  Can J Appl Sport Sci. 1982;  7 4-13
• 7 Dill D B, Myhre L G, Phillips E E, Brown D K. Work capacity in acute exposure to altitude.  J Appl Physiol. 1966;  21 1168-1176
• 8 Favret F, Richalet J P, Henderson K K, Germack R, Gonzalez N C. Myocardial adrenergic and cholinergic receptor function in hypoxia: correlation with O₂ transport in exercise.  Am J Physiol. 2001;  280 R730-R738
• 9 Ferretti G, Moia C, Thomet J M, Kayser B. The decrease of maximal oxygen consumption during hypoxia in man: a mirror image of the oxygen equilibrium curve.  J Physiol. 1997;  498 231-237
• 10 Fulco C S, Rock P B, Cymerman A. Maximal and submaximal exercise performance at altitude.  Aviat Space Environ Med. 1998;  69 793-801
• 11 Gore C J, Hahn A G, Scroop G C, Watson D B, Norton K I, Wood R J, Campbell D P, Emonson D L. Increased arterial desaturation in trained cyclists during maximal exercise at 580 m altitude.  J Appl Physiol. 1996;  80 2204-2210
• 12 Hopkins S R, McKenzie D C. Hypoxic ventilatory response and arterial desaturation during heavy work.  J Appl Physiol. 1989;  67 1119-1124
• 13 Kayser B, Narici M, Binzoni T, Grassi B, Cerretelli P. Fatigue and exhaustion in chronic hypobaric hypoxia: influence of exercising muscle mass.  J Appl Physiol. 1994;  76 634-640
• 14 Kayser B. Exercise starts and ends in the brain.  Eur J Appl Physiol. 2003;  90 411-419
• 15 Lawler J, Power S K, Thompson D. Linear relationship between V·O_2max and V·O_2max decrement during exposure to acute hypoxia.  J Appl Physiol. 1988;  64 1486-1492
• 16 Lundby C, Araoz M, Van Hall G. Peak heart rate decreases with increasing severity of acute hypoxia.  High Alt Med Biol. 2001;  2 369-376
• 17 Martin D, O'Kroy J. Effects of acute hypoxia on the V·O_2max of trained and untrained subjects.  J Sports Sci. 1993;  11 37-42
• 18 McGuire B J, Secomb T W. Theoretical predictions of maximal oxygen consumption in hypoxia: effect of transport limitations.  Resp Physiol Neurobiol. 2004;  143 87-97
• 19 Noakes T D, Peltonen J E, Rusko H K. Evidence that central governor regulates exercise performance during acute hypoxia and hyperoxia.  J Exp Biol. 2001;  204 3225-3234
• 20 Peltonen J E, Rusko H K, Rantamaki J, Sweins K, Niittymaki S, Viitasalo J T. Effects of oxygen fraction in inspired air on force production and electromyogram activity during ergometer rowing.  Eur J Appl Physiol. 1997;  76 495-503
• 21 Richalet J P. The heart and adrenergic system in hypoxia. Sutton JR, Coates G, Remmers JE Hypoxia: The Adaptations. Philadelphia, PA; BC Dekker 1990: 231-240
• 22 Richalet J P, Larmignat P, Rathat C, Keromes A, Baud P, Lhoste F. Decreased cardiac response to isoproterenol infusion in acute and chronic hypoxia.  J Appl Physiol. 1988;  65 1957-1961
• 23 Roach R C, Calbet J A, Olsen N V, Poulsen T D, Vissing S F, Saltin B. Peak exercise heart rate at high altitude.  Med Sci Sport Exerc. 1996;  28 1072
• 24 Robergs R A, Quintana R, Parker D L, Frankel C C. Multiple variables explain the variability in the decrement in V·O_2max during acute hypobaric hypoxia.  Med Sci Sports Exerc. 1998;  30 869-879
• 25 Roca J, Hogan M C, Story D, Bebout D E, Haab P, Gonzalez R, Ueno O, Wagner P D. Evidence for tissues diffusion limitation of V·O_2max in normal humans.  J Appl Physiol. 1989;  67 291-299
• 26 Roche F, Reynaud C, Pichot V, Duverney D, Costes F, Garet M, Gaspoz J M, Barthelemy J C. Effect of acute hypoxia on QT rate dependence and corrected QT interval in healthy subjects.  Am J Cardiol. 2003;  91 916-919
• 27 Squires R W, Buskirk E R. Aerobic capacity during acute exposure to simulated altitude, 914 to 2286 meters.  Med Sci Sports Exerc. 1982;  14 36-40
• 28 Stenberg J, Ekblom B, Messin R. Hemodynamic response to work at simulated altitude, 4000 m.  J Appl Physiol. 1966;  21 1589-1594
• 29 Wagner P D. Reduced maximal cardiac output at altitude - mechanisms and significance.  Respir Physiol. 2000;  120 1-11
• 30 Woorons X, Mollard P, Lamberto C, Letournel M, Richalet J P. Effect of acute hypoxia on maximal exercise in trained and sedentary women.  Med Sci Sports Exerc. 2005;  37 147-154