1. Shock the System
First Step: Exercise the circulatory system and activate brown fat. To do it, go stand in snow barefoot. Or turn the shower cold and stand under the water for a minute. Whatever the source, the goal is to give your system a little shock, then suppress your natural response to shiver. (How? Take a deep breath, and relax. You’re fine. You’re not dying today.) Doing so sends a signal to your body to find another way to warm up; this activates brown fat and boosts metabolism.
2. Dial in breath.
To alter the way your body responds to external stress — say, standing in the snow barefoot — you need to train it to metabolize oxygen more efficiently. Power breathing is the way to do it. Begin by taking 30 fast breaths. Inhale for one second, and let the exhale flow out slowly and naturally. (You may start to feel dizzy or cold or experience tingling in your hands and feet: This is normal.) After the 30 breaths, finish with an exhale and time yourself to see how long it takes before you need to gasp for air. Hold on as long as you can, clenching the muscles in your chest, arms, and legs. When you can’t stand it anymore, take in a half breath and hold it for 15 seconds. Exhale, then start over. Repeat this power-breathing process three times, increasing the length of the final hold each time.
Excerpted from mensjournal.com