Altitude training camps are frequently used by endurance athletes to increase total hemoglobin mass (Hbmass) and potentially aerobic performance. However, the effects of such intervention on red blood cell (RBC) properties remain largely unexplored, although these factors could influence the physiological responses following altitude training. This self-controlled study investigated the effects of a "live high-train high" (LHTH) altitude training camp on RBC senescence and Hbmass in nine elite swimmers. Participants performed two 4-wk training camps, one at 1,850 m altitude (LHTH) and the other one at sea level. Hbmass, hematocrit, RBC senescence, and deformability were measured before and immediately after both training camps, and again 10 days after the LHTH camp. A 400-m freestyle "all-out" swimming test was performed before and 10 days after each training camp (n = 6). Hbmass, hematocrit, CD71-positive RBCs, RBC phosphatidylserine exposure, and the percentage of RBC retaining mitochondria were increased after LHTH camp. RBC reactive oxygen species content was increased after both interventions, whereas RBC deformability and CD47 exposure remained unchanged. Although LHTH camp was accompanied by an increase in RBC senescence markers, Hbmass remained increased 10 days post-LHTH. Although 400-m swimming performance was not significantly improved 10 days post-LHTH (-3.8 ± 5.1 s), its change was associated with Hbmass variations. These results indicate that a 4-wk LHTH camp (1,850 m) is accompanied by an increase in Hbmass, which persists for up to 10 days after the camp, despite the increase in RBC senescence markers, a persistence that could be explained by a prolonged RBC survival.
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