Commentary on Point-Counterpoint

Physical fitness and hematological changes during acclimatization to moderate altitude: a retrospective study

While high altitude adaptations have been studied extensively, limited research has examined moderate altitude (MA: 1500 to 3000 m) adaptations and their time course, despite the fact that millions of people sojourn to or reside at MA. We retrospectively examined long-term MA acclimatization by analyzing recurring physical fitness test results and hematological data among 2147 college-age male cadets previously residing at either sea level (SL) or MA and currently attending the U.S. Air Force Academy (USAFA), a unique, regimented, and well-controlled military university located at 2210 m. Significant (p < 0.01) differences were found in aerobic and anaerobic fitness test scores between former SL and MA subjects, with MA subjects scoring 27 points (8%) higher during a 1.5-mile aerobic fitness run and 18 points (6%) higher than SL subjects in the anaerobic fitness test for 2 yr. These differences may be partly explained by the hematological differences observed. Hemoglobin concentration ([Hb]) was significantly (p < 0.001) higher (6.3%; approximately 1 g/dL) in MA subjects prior to arrival at USAFA and acutely, but the difference between altitude conditions was gone at the next retrospective blood draw (+17 months). After 2.5 yr at USAFA, former SL residents had significantly (p < 0.001) higher [Hb] by +10%, or 1.5 g/dL versus prearrival values. This study suggests that significant hematological acclimatization occurs with MA exposure and requires greater than 7 months to reach stability. The altitude-induced erythropoiesis may explain in part the improvements in aerobic performance, but altitude-related anaerobic differences still remain after hematological acclimatization.

Unchanged anaerobic and aerobic performance after short-term intermittent hypoxia

INTRODUCTION

Repeated short-term exposures to a severe degree of hypoxia, alternated with similar intervals of normoxia, are recommended for performance enhancement in sports. However, scientific evidence for the efficiency of this method is controversial with regard to anaerobic performance. Therefore, we conducted a randomized, double-blind, placebo-controlled study to investigate the effects of this new method on both anaerobic and aerobic performance.

METHODS

During 15 consecutive days, 20 endurance-trained men (V O2max (mean +/- SD) 60.2 +/- 6.8 mL x kg(-1) x min(-1)) were exposed each day to breathing (through mouthpieces) either a gas mixture (11% O2 on days 1-7 and 10% O2 on days 8-15; hypoxia group, N = 10) or compressed air (control group, N = 10), six times for 6 min, followed by 4 min of breathing room air for a total of six consecutive cycles. Before and after the treatment, an incremental cycle ergometer test to exhaustion and the Wingate anaerobic test were performed to assess aerobic and anaerobic performance.

RESULTS

Hypoxic treatment did not improve peak power or mean power during the Wingate anaerobic test, nor did it affect maximal oxygen uptake (V O2max), maximal power output (Pmax), lactate threshold or levels of heart rate (HR), minute ventilation (V E), oxygen uptake (V O2), or blood lactate concentration at the submaximal workloads during the ergometer test. Maximal lactate concentration (Lamax) after the tests and HRmax and maximal respiratory exchange ratio (RERmax) during the ergometer test were not significantly different between groups at any time.

CONCLUSION

The results of this study demonstrated that 1 h of intermittent hypoxic exposure for 15 consecutive days has no effect on aerobic or anaerobic performance.