It has been a common practice for some seekers of spirituality to meditate under cold conditions (under a freezing water fall, or simply wears scantily on winter months). The question is: How does it related to spirituality?
When the temperature is down to a point, our body will react naturally and will shiver. Shivering can act as heat generator, our muscles will contract, and we are ready to run away from the situation! In meditative practice, the practitioner is to train himself, or his body, NOT to act according to this "programmed" path. But to relax. The objective is NOT to shiver. In order to be into the stage of non-shivering, the mind has to be very focused and the muscles have to totally relaxed. With the body being in this condition, the meditator shall mindfully consolidate his chi at the centre of his body, and mindfully allow it to move to every (extension) muscles, so that one's finger tips will be full of chi too (felt as having internal pressure).
Any meditator who has taken this route of practice can appreciate the difficulty and the need of a focused (void) mind to make it possbible not to shiver in freezing conditions! And each session will be a challenge, no matter how many successful sessions that one went through in the past!
It is like the diffusion of one's non-spiritual impulse, like greed, like anger, like obsession ( Buddhist lingo:贪、嗔、痴), no matter how spiritual one has become, every situation conducive of such impulse will be a challenge to a person seeking spirituality (like it is nice when others praise your blog, not so nice [getting angry?] when someone condemns it!).
Hopefully the training to relax under freezing conditions can be carried over to other situations that test our spirituality!