Ten athletes (22.4 ± 3.6 years) practicing distance runnig at an international level (800m in 1’49”66, 1500 in 3’41”; 3000m steeplechase in 8’46”; 5000m in 14’14”) were evaluated in trackfield by a gradual maximum test, based on the test of Leger and al (1983). The test was done before a stay of 4 weeks at medium altitude (1800 m), and fifteen days after the return to sea level. These athletes have been subjected to a blood test, on the blood parameters usual (before and after their stay in altitude). The results show a greater energy expenditure for most levels above 15 km / h, and a lower VMA to the return at sea level. Indeed curve speed-heart rate showed higher values once the placement aloft for all levels greater than 14 km / h and a lower VMA km / h. The hypothesis of an overload for high-altitude training would explain this state of fatigue. Yet on a systematic hematologic improvement among all athletes studied is observed for red blood cells (GR), hematocrit (Ht) and hemoglobin (Hb). In sum blood factors determining the enhancement of transport of blood have been improved, which should have had a positive impact on performance. The results of these same athletes in competition did not follow and further support this hypothesis, since none of the athletes in question could not repeat the “times” were made before the stay aloft. The altitude training seems to have developed the capability to support athletes training loads important, but has not had the expected results in competition. These results should they be confirmed and call coaches to a more efficient use of training stays (choice of load periods and training) in altitude and confirm other hand, the absence of real and direct impact recent performance in the bottom half.