What Causes a Lack of Energy & Weakness During Workouts?

Overexercise can sap your energy.
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If your exercise routine feels like it's putting the "work" in workout, it's time for some troubleshooting. Moderate activity shouldn't make you feel weak and weary, so if your legs are turning to noodles on the treadmill, there's definitely something wrong. When even light exercise is hard to muster, see a doctor pronto. It's important to rule out medical conditions such as anemia, kidney disease, liver disease or abnormal thyroid levels.

Exercise and Energy

    Under healthy circumstances, exercise should fuel your energy, not drain it. Using your muscles makes them stronger, and the increased blood flow helps distribute oxygen and vital nutrients to your brain, organs and other tissues. Working out also improves your mood, which by itself can lead to increased energy. Cardiovascular exercise also improves function in your heart and respiratory system, allowing you to tackle everyday activities with greater ease. If you had low energy levels before you started exercising, you may find over time that your workouts get easier.

Overtraining Syndrome

    If you've plunged headfirst into an intense workout routine, you may be exhausting yourself with exercise. Throwing more stress at your body than it can handle leads to overtraining, leaving you fatigued and unable to tolerate workouts. Symptoms of overtraining include loss of energy, lack of concentration, sleeplessness, headaches, twitching, loss of appetite, decreased performance, dehydration, reduced immune function and elevated pulse. If this describes you, walk away from the gym and don't return for at least three to five days. Get plenty of sleep, and if symptoms persist, then see your doctor. Once you've healed, ease into your exercise routine slowly.


    A dehydrated body is a weaker body. Lack of fluid can reduce your energy, hindering athletic performance and sabotaging your workout goals. One way to test your hydration level is to check your urine. Strive to keep it clear in color; if it's dark yellow, you need a tall glass of water. Keep your insides properly moistened by drinking three cups of water in the two to three hours leading up to your workout. Have half a cup every 20 minutes during your workout, and two more cups as soon as you stop.


    Calories equal energy, and you need vitamins and minerals to operate at peak performance. If your diet is poor or overly restricted, your workout may be suffering. The University of San Francisco Medical Center recommends eating a light meal two to four hours before working out. It should include plenty of complex carbohydrates, found in pasta and bread, a serving of protein and a small amount of fat. Try a reduced-fat cheese sandwich with lettuce, tomato and onions on whole wheat bread, along with 2 cups of air-popped popcorn. After exercising, eat a snack within 15 minutes for recovery. Eat no fewer than 1,200 calories each day.

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