Wiped out during your workouts? Too pooped to even start exercising? Not getting the results you want? When exercise feels hard, you're more likely to get frustrated and quit. But exercise fatigue is easy to fix.

Here are four ways to stop the energy drain—and maximize your workouts.

Pump up iron

Exercise can feel harder than it should if you're low in iron, a mineral that helps convert food into energy, says Jere D. Haas, Ph.D., director of nutritional sciences at Cornell University in Ithaca, NY. In a study of 42 iron-depleted (but not anemic) women, researchers gave half the group iron supplements while the other half got placebos. After exercising for four weeks, the women taking iron were able to finish their exercise routine 12 percent faster, while the placebo group only improved by 5 percent (Jour. of Applied Physiology, March 2000).

Dieting, avoiding meat and having heavy menstrual periods can put you at risk for low iron. To avoid this risk, make sure you're getting the recommended 18 mg of iron every day by eating lean meat or legumes, leafy greens and whole grains along with citrus fruit and juice with vitamin C, which improves iron absorption from plant foods. Check with your doctor before taking iron supplements.

Skip daytime dieting

If you're cutting calories to lose weight, you're likely cutting the carbohydrates, protein and nutrients you need for energy, says Nancy Clark, R.D., author of Nancy Clark's Sports Nutrition Guidebook (Human Kinetics, 1997). "My motto is fuel by day, diet by night," she says. "Eat a solid breakfast, lunch and snacks during the day to get plenty of energy for your daytime activities. Then eat a light dinner to create a calorie deficit at night. When you're fueling properly, you should wake up hungry."

Hit the bottle

Think you don't need your water bottle for workouts shorter than an hour? Think again. "Research shows that you can get dehydrated in as little as 45 to 50 minutes—and that can drag your energy down," Clark says. "Take a sip of water every 15 to 20 minutes while you work out." And remember to drink at least eight glasses of water throughout the day—otherwise you could be dehydrated before you even start exercising.

Snack first

"Exercising on an empty stomach can really hurt your performance," Clark says. In one small study, cyclists who ate a small meal before exercising were able to ride almost 30 minutes longer than those who pedaled on an empty stomach (Medicine & Science in Sports & Exercise, March 1999). Try having some yogurt, a banana, or some graham crackers before your workout, and you'll have more energy to exercise.