The surprisingly easy way to tell if you’re working out too much

Overtraining syndrome, a condition characterized by too much strenuous exercise with too little rest, can really mess with your body. According to a review published in the journal Sports Health, overtraining can cause symptoms ranging from mood swings to muscle loss, and may even result in chronic inflammation or a poor immune system.

Some more clearly connected warning signs include things like fatigue, dreading workouts and abnormal muscle pain. But a more subtle sign may also arise: As a result of overtraining, you will probably end up with a faster resting heart rate.

Your resting heart rate is the speed of your pulse when you are completely at rest. It can be measured while you are sleeping or while you are lying down and unengaged in any activity. Resting heart rates are typically lower in those who are physically fit and higher in those who rarely or never exercise. According to the American Heart Association, the average person’s resting heart rate is between 60 and 100 beats per minute. An athlete’s resting heart rate may venture lower, around 40 beats per minute.

But if your body is strained because you are exercising too much, your resting heart rate will start to speed up. A study in the Journal of Sports Sciences monitored the exercise frequency, exercise intensity and heart rates of a group of trained cyclists. When the participants overtrained, their resting heart rates increased. A review in the journal Sports Health showed a connection between overtraining and heart rate responses of the nervous system (often characterized by large fluctuations in heart rate or abnormal increases). The researchers hypothesize that these reactions may be due to stress and inflammation, though more research is needed.

Of course, feeling your heart racing while you’re exercising is completely normal, and probably something to aim for. But if your heart rate is higher than normal long after you’ve left the gym, it could be time to take a rest.

This isn’t the only thing your heart rate can communicate. Here are some other interesting things your heart rate can tell you about your health.