Women are better protected against such variations than men. A classic example of this was in the Blackpool 48 Hour race held in November 1988. 24 hour and 48 hour performers faced a group of top women ultra runners. In that race, women finished 1st, 3rd, 6th and 7th . Cold is just one of a host of variables that may have to be faced in the course of a long ultra.
Heat is another problem.
It is possible that women, being generally smaller and especially having a lower total muscle mass generate less body heat and are therefore able to dissipate this heat more effectively. Although speed, strength and running endurance are still important factors, another major asset is the ability to handle prolonged stress, both physical and mental. Possibly this ability comes in part from the female's need to cope with the prolonged stress of childbirth. In past centuries women unable to cope with such stress would not have survived, nor in all probability would their offspring. Thus evolution over countless generations has discriminated in favour of stress-resistant women.