Training, simply put, is adding specific stress to the body. Your body then adapts to the stress load, and gets stronger, faster, or more powerful.  But there are times when completing your work out more of a detriment to your goals and perhaps your health. Understanding when to cease training will not only reduce your risk of injury, it will ultimately make you a faster, more efficient and productive athlete.

When you are sick : You may not need to stop your training with a minor cold, but if you have a more severe illness your body needs to devote its energy to healing itself, just like an injury. Generally, if your symptoms are above the neck (nasal congestion), you may be able to train. If your symptoms are below the neck, such as gastrointestinal problems, upper respiratory issues, fever, body aches, and sore throat you should wait until you are better.

When you get a get a "pull" : In my experience, the body usually gives you an indicator when an injury is impending - such as a small amount of pain when training, or a "pull" as some athletes call this.  If you listen to your body, and give it a few days to heal, the injury may quickly resolve itself. When you try to train through minor sprains and strains you will greatly increase your risk of a more serious injury that could keep you from training for some time. If you are experiencing pain when you are not exercising, or when you are trying to sleep, you definitely need to let your injury heal before placing further stress on the body.

When you are over-stressed: Training can help alleviate stress, but when you already have a high stress load placed on you from work, family, etc., sometimes it is best to take a day off. This is largely a judgment call of course, but if your sleep has been affected and you are already exhausted from a tough day at work, it may be more productive to rest your body over breaking it down further.

When you are hung over: Alcohol dehydrates the body, limits quality sleep, depletes electrolytes, and affects a variety of other body systems. Getting up after a night on the town and training can be dangerous. Make sure you are re-hydrated before resuming training.

When your body is not ready to train:  A balanced training plan is crucial to athletic success. For instance; adding another high intensity work before are fully recovered from the last will not be productive. This breaks the stress-recovery cycle. Instead of stress-recovery, your training becomes stress-stress and further breaks down the body. This will make you slower instead of faster and increases the risk of injury.

When you are not mentally prepared or focused: Often once you start your work out, and the endorphins start flowing, you will enter into a more prepared state of mind. Getting started is often the hardest part. Generally speaking, as intensity is increased your training will require more focus and mental energy. No more than 2-3 "break-through" work outs per week are recommended. These key workouts advance your fitness and are sequential. If you are having a day where you just do not have what it takes to perform a break-through work out, reschedule it for another day. If you cannot put forth a good effort, going through the motions is not necessarily productive.

When you have more important responsibilities: I advise all my athletes to seek a balance with their lifestyles. Family and job responsibilities must come first.  Accept that there will be times when you must miss a work out due to these other responsibilities. When you invest a lot of time and energy in your training this can be frustrating, but it is more important to have your priorities in order.

Athletes are highly driven and motivated people that do not like to lose ground. Even though most of the above are common sense, we have all trained when we probably should not have. As a rule, if you really feel you need a day off you should take it off. It is far better to be conservative in your training than risk over training or an injury that could end your season.