Exercise can be taxing, but if your body is pushed too close to its limits, it can become dangerous. Most exercise experts recommend keeping your workout intensities to less than 80 percent of your maximum heart rate if you're exercising for a sustained period of time. If you develop shaking during exercise or become very exhausted, your body is telling you to take it easy and rest. It is also possible that you have drained the body of nutrients, including blood sugars.
When exhausted, you will find it difficult to continue physical activity. Your muscles will feel weak and slow to respond. You may also feel lightheaded and suffer from some dizziness. Your heart may seem to be beating excessively fast. In more extreme cases, you may also suffer from nausea and vomiting. Shaking is easier to identify; you will experience uncontrollable tremors either in a select group of muscles or throughout your body, particularly in extremities such as the hands.
The most common cause of shaking and exhaustion is a condition called hypoglycemia. This is a temporary state in which the body's blood sugar levels have run low, zapping your body of energy. Blood sugar levels are sustained by the sugars and carbohydrates in your diet and when you go for a long time without eating they can drop and make it difficult to function. Exercising also taps your blood sugars for fuel and can wear the body out. It is also possible that you have simply pushed your body to an extreme point where it struggles to control its motor function, leading to shaking in your body's muscles.
Treatment and Prevention
Stop exercising if shaky or exhausted and sit down. Take deep breaths to deliver oxygen to the body and sip water or, even better, a sports drink -- the sugars in sports drinks will restore your body's blood sugar levels and you may experience some improvement in your condition, particularly your shaking. If you have access to food, you may want to eat a small amount to see if that also improves your condition by providing fuel to your body and sugars to your blood. You can prevent exhaustion and shaking from occurring by eating a small amount prior to exercising or drinking a sports drink before and/or during your exercise.
If you have other unexplained symptoms or if your treatment of the symptoms does not yield any improvement, consult a doctor for a diagnosis. It is possible you are suffering from a combination of problems or that you are dealing with a condition that is difficult to identify without professional insight. Under no circumstances should you push yourself to continue exercising while experiencing exhaustion and uncontrollable shakes.