Intermittent Hypoxia Increases Erythropoietin Levels in Healthy Individuals

Few minutes of hypoxic exposure stabilizes hypoxia-inducible factor-1α, resulting in erythropoietin (EPO) gene transcription and production. PURPOSE: The objective of this study was to identify the shortest intermittent hypoxia protocol necessary to increase serum EPO levels in healthy individuals. We hypothesized that two separate intermittent hypoxia protocols would significantly increase EPO levels in healthy individuals. METHODS: A total of seven individuals (4 women and 3 men, age: 28±7 years, height: 177±9 cm, weight: 79.7±18.4 kg) participated in the study. In Experiment 1, the spontaneous EPO changes under normoxia (NORM) and the EPO response to five 4-minute cycles of intermittent hypoxia (IH5) were determined in six individuals. In Experiment 2, the EPO response to eight 4-minute cycles of intermittent hypoxia (IH8) and 120 minutes of continuous hypoxia (CONT) was determined in six individuals. All hypoxic protocols were performed at a targeted arterial oxygen saturation of 80%. Air was made hypoxic by titrating nitrogen into a breathing circuit. Pulmonary gas exchange, arterial oxygen saturation, and hemodynamics obtained by finger plethysmography were continuously monitored throughout all hypoxic protocols. In Experiment 1, EPO levels were measured before, 2.5 and 4.5 hours after the beginning of the IH5 and NORM protocols. In Experiment 2, EPO levels were measured before, 4.5 and 6 hours after the beginning of the IH8 and CONT protocols. RESULTS: There was no significant change in EPO levels in response to normoxia or in response to five cycles of intermittent hypoxia (NORM: 9.5±1.8 to 10.5±1.8, IH5: 11.4±2.3 to 13.4±2.1 mU/ml, main effect for time p=0.35). There was an increase in EPO levels in response to eight cycles of intermittent hypoxia and 120 minutes of continuous hypoxia, with peak levels observed 4.5 hours after the onset of hypoxia (IH8: 11.2±2.0 to 16.7±2.2, CONT: 11.1±3.8 to 19.4±3.8 mU/ml, main effect for time p˂0.01). Eight cycles of intermittent hypoxia increased EPO levels to a similar extent as 120 minutes of continuous hypoxia (main effect for condition p=0.36). Intermittent hypoxia did not affect mean arterial pressure (IH5: 88±7 to 87±7, IH8: 90±7 to 88±7 mmHg, p\u3e0.05). CONCLUSION: Eight 4-minute cycles of intermittent hypoxia represent the shortest protocol to increase serum EPO levels in healthy individuals

Ischemic preconditioning improves maximal performance in humans

Repeated episodes of ischemia followed by reperfusion, commonly referred to as ischemic preconditioning (IPC), represent an endogenous protective mechanism that delays cell injury. IPC also increases blood flow and improves endothelial function. We hypothesize that IPC will improve physical exercise performance and maximal oxygen consumption. The purpose of the study was to examine the effect of ischemic preconditioning in leg skeletal muscles on cycling exercise performance in healthy individuals. Fifteen healthy, well-trained subjects performed two incremental maximal exercise tests on a bicycle ergometer. Power output, oxygen consumption, ventilation, respiratory quotient, and heart rate were measured continuously. Blood pressure and blood lactate were measured before and after the test. One exercise test was performed after the application of ischemic preconditioning, using a protocol of three series of 5-min ischemia at both legs with resting periods of 5 min in between. The other maximal cycling test served as a control. Tests were conducted in counterbalanced order, at least 1 week apart, at the same time of the day. The repeated ischemic periods significantly increased maximal oxygen consumption from 56.8 to 58.4 ml/min per kg (P = 0.003). Maximal power output increased significantly from 366 to 372 W (P = 0.05). Ischemic preconditioning had no effect on ventilation, respiratory quotient, maximal heart rate, blood pressure or on blood lactate. Repeated short-term leg ischemia prior to an incremental bicycle exercise test improves maximal oxygen consumption by 3% and power output by 1.6%. This protocol, which is suggested to mimic the effects of ischemic preconditioning, may have important implications for exercise performance

Performance of runners and swimmers after four weeks of intermittent hypobaric hypoxic exposure plus sea level training.

This double-blind, randomized, placebo-controlled trial examined the effects of 4 wk of resting exposure to intermittent hypobaric hypoxia (IHE, 3 h/day, 5 days/wk at 4,000-5,500 m) or normoxia combined with training at sea level on performance and maximal oxygen transport in athletes. Twenty-three trained swimmers and runners completed duplicate baseline time trials (100/400-m swims, or 3-km run) and measures for maximal oxygen uptake (V̇