An apple a day isn't the only thing that can keep the doctor away — exercise has been proven as a key proponent in ailing a number of health issues: anxiety, insomnia, back pain, hot flashes — you name it. And of course, that added bonus of blasting fat away doesn't hurt either!

"When it comes to preventing health problems, exercise is one of the best medicines we have," says David Katz, MD, founding director of the Yale University Prevention Research Center. Some workouts are better than others at working out different issues, and fortunately Jessica Girdwain of Health.com has rounded up some known fitness fixes to heal your most common mind and body ailments:

Sleep troubles
Whether you're a troubled sleeper, or a daytime snoozer, adding a sweat session to your daily routine can prove helpful when you hit the sack. "Exercisers fall asleep faster, suffer fewer middle-of-the-night wake-ups and have a reduced risk of sleep disorders," says study co-author Brad Cardinal, PhD, co-director of the sport and exercise psychology program at Oregon State University. Cardinal attributes a lower core body temperature and an increase in the sleep-promoting hormone melatonin as two of the main reasons why activity preps your body for a good night's sleep.

Don't have enough time to juggle work, family and the gym? Try working out on your lunch break instead. And this way, not only will a little exercise keep you alert, studies show a midday sweat sesh can also make you more productive at the office and increase job satisfaction. Lunch workouts are perfect for exercisers who dread the morning and for those of us who are too tired to schlep to the gym after a long day at the office. You can find out where to get a midday workout in Philly here >>

Your fitness Rx: "A 2011 study found that people who meet the recommended physical activity guidelines of 150 minutes a week are 65 percent less likely to feel tuckered out during the day," writes Girdwain. If you're looking a low-impact workout, practicing yoga and it's deep-breathing techniques have been found to relieve insomnia. But to get the most restful sleep possible, try to wrap up your workout three hours before your crash, so you don't go to bed over stimulated.

Food cravings
Find yourself rummaging in your desk drawer for something sweet in the middle of the afternoon? If willpower isn't enough to keep you from raiding your chocolate stash, a little exercise can easily do the trick. "In the throes of a craving, your brain is saying 'feed me dopamine!' — that neurotransmitter that taps into the reward center of your brain. You can satisfy the call with carbs — or with exercise," says John Ratey, MD, author of Spark: The Revolutionary New Science of Exercise and the Brain. So if you're looking to sport a toned beach body this summer, looks like your only way to stave the craving is to hit the gym!

Your fitness Rx: According to Girdwain, "When you get the vending machine crazies, take 15 minutes and go for a brisk walk, which was shown in recent research to be all it takes to short-circuit food cravings."

Weak immune system
Ever notice how those fitness fiends at your gym are hardly ever hit with a cold? Yea, there's a reason for that. "Aerobic workouts are a natural cold-fighter, coaxing immune cells out of body tissues and into the bloodstream, where they attack invading viruses and bacteria," explains David Nieman, DrPH, a professor at Appalachian State University, whose research shows that five days of cardio a week reduced sick days by 43 percent.

Your fitness Rx: "Workouts that raise your heart rate can improve immunity — try jogging outside or taking a spinning class," writes Girdwain. Even a circuit workout for 30 minutes a day can do the trick. But the key is to avoid burning yourself out when you exercise — workouts over 90 minutes can actually increase your risk of getting sick!

For the full list, check out Health.com.