Typically runners exert their lungs the most if compared to Mountaineers. I am strictly not comparing with Swimmers of course.
First, why would it happen, how do you know whats happening:
Do we normally catch cold, runny nose when its cold outside? Normally we do. "How much cold" can vary from person to person though. Getting runny nose is one of the body's defense mechanisms. Phlegm is the substance that contains mucus (a protective substance) and other bacteria, bluntly saying which is produced by Respiratory System, to be precise by Mucus Membranes.
Respiratory Mucus protects the whole Respiratory tract and the lungs by trapping foreign particles that are inhaled through the nose when we breathe. It also helps to heat-up the inhaled air before it reaches the lungs.
- If you have a runny nose, its okay. Still try and breathe through Nose and not through mouth.
- Obviously, it is going to be difficult to breathe through nose and so doing a strenuous tasks with same efficiency as normal is a difficult task to pull off. You are not supposed to exert.
- Important: Don't choose to clean up your nose by means of Otrivin or similar products and continue getting into colder regions. This would make you feel better, but only for a while. Should you continue with your task, getting into colder regions thinking that you have now knocked the running nose issue off and are now good to get colder, Beware, it may result in constricting bronchial tubes which would exert lungs a lot and would definitely make breathing a lot difficult. Common symptoms of such a situation is coughing up blood. Taa-dan, you need help now.
(May be not entirely needed for this answer, but interesting: Why would lungs exert, its because you don't warm your lungs enough, Mucus around the Lung Fibers and tissues isn't enough, the bronchial muscles get dry, resulting in constriction.)
- Get into warmer conditions.
- Continue to breathe through nose.
- Take cloth, breath-out/exhale through mouth on it, and put it on your nose, feels warm and better. (I am not thinking of Bad-breath here)
- Put on an additional layer of clothing on your upper body half, like an additional jacket or something.