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

 

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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.

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Pascal Mollard

Laboratoire “Réponses cellulaires et fonctionnelles à l'hypoxie”

74 rue Marcel Cachin

93017 Bobigny Cedex

France

Phone: 33 1 48 38 77 57

Fax: 33 1 48 38 77 77

Email: pascal.mollard@laposte.net