Dose ” of Altitude Training : How High to Live for Optimal

23 Chronic living at altitudes ~2500m causes consistent hematological acclimatization in most, but 24 not all, groups of athletes; however, responses of erythropoietin (EPO) and red cell mass to a 25 given altitude show substantial individual variability. We hypothesized that athletes living at 26 higher altitudes would experience greater improvements in sea level performance, secondary to 27 greater hematological acclimatization, compared to athletes living at lower altitudes. After 4 28 weeks of group sea level training and testing, 48 collegiate distance runners (32M, 16W) were 29 randomly assigned to one of four living altitudes (1780m, 2085m, 2454m, or 2800m). All 30 athletes trained together daily at a common altitude from 1250m 3000m following a modified 31 Live High – Train Low model. Subjects completed hematological, metabolic, and performance 32 measures at sea level, before and after altitude training; EPO was assessed at various time points 33 while at altitude. Upon return from altitude, 3000m time trial performance was significantly 34 improved in groups living at the middle two altitudes (2085m and 2454m) but not in groups 35 living at 1780m and 2800m. EPO was significantly higher in all groups at 24h and 48h, but 36 returned to sea level baseline after 72h in the 1780m group. Erythrocyte volume was 37 significantly higher within all groups after return from altitude, and was not different between 38 groups. These data suggest that when completing a 4 week altitude camp following the Live 39 High – Train Low model, there is a target altitude between 2000m and 2500m that produces an 40 optimal acclimatization response for sea level performance. 41