Simple: just use your breath!

Here are 3 quick tips to keep you warm and loose (other than by wearing a jacket):

1. Keep your serratus (the muscle under your armpit) engaged, so that your shoulders and upper back can remain more relaxed
2. When you’re huddled and bracing into the cold, take deep belly breaths
3. Practice the Wim Hof breathing technique

I demonstrate this heating and oxygenating breath in the video below. Enjoy, and keep warm!