With the introduction of the optimized CO-rebreathing method scientists were able to study the basic regulation of tHb-mass. The total amount of haemoglobin depends on various factors as genetics, sex, anthropometric characteristics, altitude exposure, and state of training. It has been hypothesized that mainly the genetic make-up is responsible for the development of tHb-mass. It is also well known that tHb-mass correlates well with LBM (Schumacher et al. 2008) which partly also explains that men posses higher tHb-mass then women.

Interestingly, tHb-mass increases with age during childhood and adolescents (Eastwood 2009) but plateaus during adulthood. Therefore, it is a very stable parameter with a variation of <2% in moderate active men (Eastwood et al. 2008).
But also in well trained endurance athletes the variation is only 2.2% throughout the training year (Prommer et al. 2008). In case of blood withdrawal (~550ml whole blood) tHb-mass is reduced by 75 ± 15g and recovers to the original level after 36 ± 11days (Pottgiesser et al. 2008) .