Injecting hemoglobin would have no impact on aerobic conditioning. As a result that during resting conditions your body's hemoglobin is ~97% saturated with oxygen. The lowest known levels during exercise I believe are in the low 80s% saturated. Therefore, oxygen is not the limiting reagent in aerobic capacity. You should be more concerned with oxidative capacity at the cellular level (myoglobin, capillary beds, mitochondrial concentration).