This is a challenge for me....if the temp is much below 45 or 50 degrees, I have a very hard time running outside. My lungs litterally hurt and feel like they are freezing up on me. I have tried doing intervals to "build-up", but I keep hitting this point of where my lungs are just too cold and hurt. It is almost like an asthma attack triggered by the cold and activity. I have tried scarves and masks to help buffer the cold air, but they always feel too restrictive of air flow. In warmer air, I am fine and find that I do well in 65-80 degree air. Any comments or suggestions would be appreciated.