It has been reported that, within endurance-trained males, serum testosterone level significantly decreased as compared to their untrained age-matched counterparts.1 Also it has been reported that level of testosterone was associated with altitude.2 There is now abundant evidence that the offspring sex ratio at birth in mammals is partially dependent on the hormone levels of both parents around the time of conception.3 The offspring sex ratio at birth (SRB, the male proportion) of a sample of male runners varied significantly by their weekly training distance.4 Also, it has been reported that SRB was associated with altitude.5 Taken together, it is speculated that offspring SRB mountain …