Buddhist Monks raising Body Temperature?

Hello all,
I saw a TV special one time that showed how these certain Buddhist monks in the mountains of Tibet could mentally raise their internal thermostat i.e. their body temperature. Significantly.
In the cold winter, girded only in a loincloth, they would wrap wet sheets around their bodies and steam them dry, turning the room almost into a sauna. And once a year they take a hike into the snowy mountains and spend the entire night there (in meditation). A camera crew went with them one time to document it and they were freezing cold even with all of their heavy winter gear whereas the monks were only wearing light robes.
Now this does not involve yoga, per say, but I am posting this here because I think that the people in this forum are interested and possibly aware of this, as it involves energy.
The question is, have anyone ever heard of this before? And how is it possible? Any ideas or feedback welcome.

Squeaky