Journal of Sports Science and Medicine
Journal of Sports Science and Medicine
ISSN: 1303 - 2968   
Ios-APP Journal of Sports Science and Medicine
Androit-APP Journal of Sports Science and Medicine
©Journal of Sports Science and Medicine (2014) 13, 774 - 781

Research article
Influence of Acute Normobaric Hypoxia on Physiological Variables and Lactate Turn Point Determination in Trained Men
Michael Ofner1, Manfred Wonisch2, Mario Frei3,4, Gerhard Tschakert3,4, Wolfgang Domej5, Julia M. Kröpfl4,6, Peter Hofmann3,4, 
Author Information
1 Department of Sport’s and Exercise Physiology, University of Vienna, Austria
2 Department of Cardiology, Hansa Hospital Graz, Austria
3 Institute of Sports Science, Exercise Physiology & Training Research Group, University of Graz, Austria
4 Human Performance Research, University and Medical University of Graz, Austria
5 Division of Pulmonology, Department of Internal Medicine, Medical University of Graz, Austria
6 Institute of Human Movement Sciences and Sport, Exercise Physiology Lab, ETH Zurich, Switzerland

Peter Hofmann
✉ Institute of Sports Science, Exercise Physiology & Training Research Group, University of Graz, Max Mell Allee 11, 8010-Graz, Austria
Publish Date
Received: 12-03-2014
Accepted: 08-07-2014
Published (online): 01-12-2014
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The goal of this study is to evaluate the response of physiological variables to acute normobaric hypoxia compared to normoxia and its influence on the lactate turn point determination according to the three-phase model of energy supply (Phase I: metabolically balanced at muscular level; Phase II: metabolically balanced at systemic level; Phase III: not metabolically balanced) during maximal incremental exercise. Ten physically active (VO2max 3.9 [0.49] l·min-1), healthy men (mean age [SD]: 25.3 [4.6] yrs.), participated in the study. All participants performed two maximal cycle ergometric exercise tests under normoxic as well as hypoxic conditions (FiO2 = 14%). Blood lactate concentration, heart rate, gas exchange data, and power output at maximum and the first and the second lactate turn point (LTP1, LTP2), the heart rate turn point (HRTP) and the first and the second ventilatory turn point (VETP1, VETP2) were determined. Since in normobaric hypoxia absolute power output (P) was reduced at all reference points (max: 314 / 274 W; LTP2: 218 / 184 W; LTP1: 110 / 96 W), as well as VO2max (max: 3.90 / 3.23 l·min-1; LTP2: 2.90 / 2.43 l·min-1; LTP1: 1.66 / 1.52 l·min-1), percentages of Pmax at LTP1, LTP2, HRTP and VETP1, VETP2 were almost identical for hypoxic as well as normoxic conditions. Heart rate was significantly reduced at Pmax in hypoxia (max: 190 / 185 bpm), but no significant differences were found at submaximal control points. Blood lactate concentration was not different at maximum, and all reference points in both conditions. Respiratory exchange ratio (RER) (max: 1.28 / 1.08; LTP2: 1.13 / 0.98) and ventilatory equivalents for O2 (max: 43.4 / 34.0; LTP2: 32.1 / 25.4) and CO2 (max: 34.1 / 31.6; LTP2: 29.1 / 26.1) were significantly higher at some reference points in hypoxia. Significant correlations were found between LTP1 and VETP1 (r = 0.778; p < 0.01), LTP2 and HRTP (r = 0.828; p < 0.01) and VETP2 (r = 0.948; p < 0.01) for power output for both conditions. We conclude that the lactate turn point determination according to the three-phase-model of energy supply is valid in normobaric, normoxic as well as hypoxic conditions. The turn points for La, HR, and VE were reproducible among both conditions, but shifted left to lower workloads. The lactate turn point determination may therefore be used for the prescription of exercise performance in both environments.

Key words: Hypoxia, threshold determination, performance, heart rate, spiroergometry

           Key Points
  • The lactate turn point concept can be used for performance testing in normoxic and hypoxic conditions
  • The better the performance of the athletes the higher is the effect of hypoxia
  • The HRTP and LTP are strongly correlated that allows a simple performance testing using heart rate measures only.
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