The conventional wisdom is that it's okay to exercise if you have a cold but avoid exercise if you have a fever. A simple way to remember is if you have symptoms above the neck (i.e., runny nose, sore throat, sneezing), it's okay to exercise in moderation. On the other hand, if you have symptoms below the neck (i.e., wheezing, coughing, upset stomach), nix exercise until you feel better.
If you have a cold, exercise may speed up the recovery process whereas if you have a fever, exercise may slow down the recovery process. Physical activity tends to boost your immune system so cold symptoms may diminish faster provided exercise intensity level is not too high. Always listen to your body and be aware of your heart rate, breathing rate, energy level, etc. Performing exercises such as walking, biking and/or yoga at a low-to-moderate intensity level may boost your immunity to combat infection more readily. If you overreach or overtrain (as many athletes tend to do), your risk of getting a viral infection (i.e., common cold, the flu) may increase due to a suppressed immunity level as a result of increased stress (i.e., increased cortisol release). Of course, your immunity level is dependent on many factors (i.e., stress level, age, gender, amount of quality sleep, environment, mood, fitness level, etc.).
BOTTOM LINE: Low-intensity exercise is okay when you have mild symptoms (i.e., runny nose, cough, nasal congestion, etc.) but do NOT exercise when symptoms are more severe (i.e., fever, wheezing, shortness of breath, chest congestion, diarrhea, dizziness, light-headedness, nausea, vomiting, etc.). Click the file below for more details.
Brian Danley, CFT
"Motivation is what gets you started. Habit is what keeps you going."