Recovery after hard workouts
In order to get the training benefit of hard workouts, you need adequate recovery time to let your body rebuild before your next hard workout. Otherwise, instead of a positive training effect, the results will be cumulative damage and, eventually, injury. Recovery days are easy workout days and sometimes it is best to take a day off. Typical workout weeks allow for 2-3 hard workouts alternated with 4-5 recovery days. If you run a race during a training week, the race is considered a hard workout and it should replace one of your regular hard workouts. Whether you run 2 or 3 hard workouts during a week depends on many factors including age, average weekly mileage, fitness level, etc.
There is no “right” way to train and each runner needs to learn how his or her body reacts to different overloads and what works best. Over training does not help anyone and a rest day is definitely in order when you are experiencing any of the following:
An increase in resting HR (heart rate) of five beats per minute or more
A sudden weight loss of five or more pounds
A feeling of excessive thirst
A sluggish or very tired feeling
The start of illness such as sore throat or cough
Skipping a day or a week will not cause you to fall into immediate decay. If your body tells you it needs a rest, listen! If you have missed multiple workouts, it may be necessary (and wise) to drop back to an easier schedule for several days or weeks and then gradually return to your previous schedule. That makes more sense than becoming injured and having to take an extended amount of time off.