It used to be that whenever you saw a doctor for a running injury—no matter how minor–the prescription was almost always the same: Stop running! If something is bothering you, then you stop, right?

Not really.

That type of old school medicine doesn’t sit real well with today’s runners who will do just about anything to continue running. For many runners, complete rest is simply an unacceptable treatment for most minor injuries. For a runner, complete rest is tantamount to punishment from insensitive doctors who don’t understand a runner’s psyche.

But rest is an integral part of every successful running regimen. Taking the proper rest and recovery days as part of a regular training program, can be the key component that prevents a running injury from occurring. Or, a minor injury from getting worse.

Rest does not have to be a dirty word, associated with lying on the couch with the remote on your chest while pounding a six-pack of beer and a pile of chips. Instead, rest to a runner should mean controlled activity, rather than complete inactivity. The difference between these two concepts may spell the difference between running well and being injured.

Controlled activity means cutting back or reducing speed work, mileage, hills, long runs, number of days of running or any other stressful aspect of running.

Each running workout you do places some degree of stress on the body. That’s what a workout is designed to do. Certainly, the higher the intensity and the longer the workout, the greater the stress.

If you run hard and long every day, the body will not have adequate time to adapt and recover before the next workout. Eventually, some part of your body will breakdown and you will suffer an injury.

Generally, runners need at least one or two easy or recovery days to follow every hard day of running. Certainly, easy means different things to different runners, but a recovery day may entail running half or less of what you did the day before. Or, not running at all.

Without adequate recovery, the body can’t rebuild and strengthen itself because it’s constantly under stress. That’s when you get hurt. More than half of all running injuries are the result of inadequate balance between hard and easy days of running. Most runners get hurt because they run too far, too fast or too soon after a hard workout or race.

Another by product of training which is too hard (coupled with lack of rest) is overall mental and physical fatigue. This may manifest itself as having trouble sleeping due to elevated resting heart rate, mood swings, listlessness and irritability. Physical fatigue may result in colds, flu, sore throats, stiff and sore muscles—all of which makes the runner more susceptible to injuries. The more tired a runner is, the more likely he/she will get injured.

Of course, the irony of any training cycle is you actually gain strength when you rest. That’s the body way of adapting to the stress that has been placed on it. The training effect actually takes place on easy days, not hard days. The training effect is the result of the hard workouts, but your muscular and cardiovascular functions improve when the body is resting. So obviously, rest is absolutely critical.

Here are several warning signs that you need more rest or easy, recovery days:

1. An elevated resting pulse. Take your pulse every morning just after awakening, while still in bed. To establish a base line, over the course of a week, take your pulse in the morning. After you’ve established an average, continue taking it. Whenever your pulse rate is 10 beats higher than the average at waking, this is a clear indication you are still tired from the previous day’s training and you should either take a complete rest day or run very easy on the day ahead.

2. Feel tired. This is a general feeling of fatigue and sluggishness that lasts all day during normal activities. Hard training has sapped all your energy. Again, either bag today’s workout or cut back whatever is planned.

3. Sore, tired muscles. This is a symptom of overtraining because the lactic acid which accumulated in your muscles from your previous hard workout has not yet cleared. Again, you should reduce your hard training with easy runs and/or cross-training.

4. Disturbed sleep patterns. Overtraining is a definite cause of poor sleep which may mean having difficulty settling down and getting to sleep. This is often due to an elevated heart rate.

Rest is an integral part of all training programs. You must give yourself adequate time to recover from tough, long workouts before moving on to the next one. Watch for signs of overtraining and if they present themselves, back off. Better to rest now than be injured later.