Illness and injury can happen at any time, so it is useful to know what to do if you can’t train.
If you have an injury then you need to get professional help as soon as possible. Don’t think it will go away, admit to yourself that there is an issue and start managing it. If you don’t intervene early then it could turn into something worse. You may need to do rehabilitation, make sure that you listen to advice and act accordingly.
It is now the season for colds and flu, if you do succumb to “the lurgy” then make sure you hydrate well and eat plenty of fresh fruit and vegetables, avoid dairy produce if you can, as dairy can increase mucous. This tweak of your diet will help your immune system get back on track.
As far as training goes:
“A neck check is a way to determine your level of activity during a respiratory illness,” says Neil Schachter, MD, medical director of respiratory care at Mount Sinai Medical Centre in New York. “If your symptoms are above the neck, including a sore throat, nasal congestion, sneezing, and tearing eyes, then it’s OK to exercise,” he says. “If your symptoms are below the neck, such as coughing, body aches, fever, and fatigue, then it’s time to hang up the running shoes until these symptoms subside.”
I would still be cautious about exercising when ill, your immune system is taking a battering, and you may find that exercising makes you feel worse. If in doubt go out, but take it easy. You really need to use your own judgment on this, sometimes going out when you are not recovered can set you back more than resting and allowing your body to balance itself.
If you do miss training due to illness then these guidelines (from Don Fink) will help you to work out what to do
1 day missed
Just skip your workout. Missing one workout will not matter in the long run.
2-3 days missed
Skip the lost days and rejoin your normal training, but on the first day back do half of your scheduled workout. Resume normal training on the second day back.
4-6 days missed
Rejoin programme skip the missed days. Do 1/3 of your scheduled training on first 2 days back, and 2/3rds on next 2 days back. Resume full training on the fifth day back.
7 or more days missed
You may need to reconsider your goals depending on when this happens. Speak to your coach, if you have one, and modify your training plan.
As I said these are guidelines, and I think that it is more important for you to decide what the best course of action is. Only you really know how well you are recovered.