As a result , mixed - sex events are most often held with a relay race format .
In non-vehicular racing sports the physiological differences between the sexes often preclude head - to - head competition between people of different sexes at the elite level .
Mixed - sex events are most often held with a relay race format .
In non-vehicular racing sports the physiological differences between the sexes often preclude head - to - head competition between people of different sexes at the elite level .