Experts say there is no magic to exercise: You get out of it what you put in. That doesn't mean you have to work out for hours each day. It just means you need to work smart.
That said, experts agree that not all exercises are created equal. Some are simply more efficient than others, whether they target multiple muscle groups, are suitable for a wide variety of fitness levels, or help you burn calories more effectively.
So what are the best exercises? We posed this question to four fitness experts and compiled a list of their favorites.
Any exercise program should include cardiovascular exercise, which strengthens the heart and burns calories. And walking is something you can do anywhere, anytime, with no equipment other than a good pair of shoes.
It's not just for beginners, either: Even the very fit can get a good workout from walking.
"Doing a brisk walk can burn up to 500 calories per hour," says Robert Gotlin, DO, director of orthopaedic and sports rehabilitation at Beth Israel Medical Center in New York. Since it takes 3,500 calories to lose a pound, you could expect to lose a pound for every seven hours you walk, if you did nothing else.
Don't go from the sofa to walking an hour day, though. Richard Cotton, a spokesman for the American Council on Exercise, says beginners should start by walking five to -10 minutes at a time, gradually moving up to at least 30 minutes per session.
"Don't add more than five minutes at a time," he says. Another tip: It's better to lengthen your walks before boosting your speed or incline.
2. Interval training
Whether you're a beginner or an exercise veteran, a walker or an aerobic dancer, adding interval training to your cardiovascular workout will boost your fitness level and help you lose weight.
"Varying your pace throughout the exercise session stimulates the aerobic system to adapt," says Cotton. "The more power the aerobic system has, the more capacity you have to burn calories."
The way to do it is to push the intensity or pace for a minute or two, then back off for anywhere from two to -10 minutes (depending on how long your total workout will be, and how much time you need to recover). Continue doing this throughout the workout.
Strength training is essential, the experts say. "The more muscular fitness you have," says Cotton, "the greater the capacity you have to burn calories."
And our experts tended to favor strength-training exercises that target multiple muscle groups. Squats, which work the quadriceps, hamstrings, and gluteals, are an excellent example.
"They give you the best bang for the buck because they use the most muscle groups at once," says Oldsmar, Fla., trainer David Petersen.
Form is key, though, warns Petersen.
"What makes an exercise functional is how you perform the exercise," he says. "If you have bad technique, it's no longer functional."
For perfect form, keep feet shoulder-width apart and back straight. Bend knees and lower your rear, says Cotton: "The knee should remain over the ankle as much as possible."
"Think of how you sit down in a chair, only the chair's not there," suggests Gotlin.
Physical therapist Adam Rufa, of Cicero, N.Y., says practicing with a real chair can help.
"Start by working on getting in and out of a real chair properly," he says. Once you've mastered that, try just tapping the chair with your bottom, then coming back up. Then do the same motion without the chair.
Gotlin sees lots of patients with knee pain, and says quadriceps weakness is the cause much of the time. If you feel pain going down stairs, he says, strengthening your quads with squats may very well help.
Like squats, lunges work all the major muscles of the lower body: gluteals, quadriceps, and hamstrings.
A lunge is a great exercise because it mimics life, it mimics walking," only exaggerated, says Petersen.
Lunges are a bit more advanced than squats, says Cotton, helping to improve your balance as well.
Here's how to do them right: Take a big step forward, keeping your spine in a neutral position. Bend your front knee to approximately 90 degrees, focusing on keeping weight on the back toes and dropping the knee of your back leg toward the floor.
Petersen suggests that you imagine sitting on your back foot. "The trailing leg is the one you need to sit down on," he says.
To make a lunge even more functional, says Rufa, try stepping not just forward, but back and out to each side.
"Life is not linear, it's multiplanar," says Rufa. And the better they prepare you for the various positions you'll move in during the course of a day, the more useful exercises are.
If done correctly, the push-up can strengthen the chest, shoulders, triceps, and even the core trunk muscles, all at one time.
"I'm very much into planking exercises, almost yoga-type moves," says Petersen. "Anytime you have the pelvis and the core [abdominals and back] in a suspended position, you have to rely on your own adherent strength to stabilize you."
Push-ups can be done at any level of fitness, says Cotton: "For someone who is at a more beginning level, start by pushing from the kitchen-counter height. Then work your way to a desk, a chair, the floor with bent knees, and, finally, the floor on your toes."
Here's how to do a perfect push-up: From a face-down position, place your hands slightly wider than shoulder-width apart. Place your toes or knees on the floor, and try to create a perfect diagonal with your body, from the shoulders to the knees or feet. Keep the glutes [rear-end muscles] and abdominals engaged. Then lower and lift your body by bending and straightening your elbows, keeping your torso stable throughout.
There are always ways to make it harder, says Rufa. Once your form is perfect, try what he calls the "T-stabilization" push-up: Get into push-up position, then do your push-ups with one arm raised out to the side, balancing on the remaining three limbs without rotating your hips.
6. Abdominal Crunches
Who doesn't want firm, flat abs? Experts say that when done correctly, the familiar crunch (along with its variations) is a good choice to target them.
For a standard crunch, says Cotton, begin lying on your back with feet flat on the floor and fingertips supporting your head. Press your low back down and begin the exercise by contracting abdominals and peeling first your head (tucking your chin slightly), then your neck, shoulders, and upper back off the floor.
Be careful not to pull your neck forward by sticking the chin out; don't hold your breath, and keep elbows out of your line of vision to keep chest and shoulders open.
For his part, Petersen teaches his clients to do crunches with their feet off the floor and knees bent. He says that with feet kept on the floor, many people tend to arch the back and engage the hip flexors.
"Crunches can be excellent, but if they're not done correctly, with the back arching, they can actually weaken the abdominals," Petersen says.
To work the obliques (the muscles on the sides of your waist), says Cotton, take the standard crunch and rotate the spine toward one side as you curl off the floor.
"Twist before you come up," he says. "It's really important that the twist comes first because then it's the obliques that are actually getting you up."
But keep in mind that you won't get a flat stomach with crunches alone, says Cotton. Burning belly fat requires the well-known formula: using up more calories than you take in.
"Crunches work the ab muscles; [they're] not to be mistaken as exercise that burns the fat over the abdominals," he says. "That's the biggest myth in exercise going." Learn more about the best ab exercises and how to perform them.
7. Bent-over Row
Talk about bang for the buck: This exercise works all the major muscles of the upper back, as well as the biceps.
Here's how to do it with good form. Stand with feet shoulder-width apart, then bend knees and flex forward at the hips. (If you have trouble doing this exercise standing up, support your weight by sitting on an incline bench, facing backward.) Tilt your pelvis slightly forward, engage the abdominals, and extend your upper spine to add support. Hold dumbbells or barbell beneath the shoulders with hands about shoulder-width apart. Flex your elbows, and lift both hands toward the sides of your body. Pause, then slowly lower hands to the starting position. (Beginners should perform the move without weights.)
These seven exercises are excellent, efficient choices, the experts say. But with just about any strength or resistance exercise, says Petersen, the question is not so much whether the exercise works as how well you execute.
"Done with good technique, all exercises do what they're supposed to do," says Petersen.
The trouble is that poor form can change the whole exercise, putting emphasis or even strain on different areas than intended. This can hurt, rather than help you.
So especially if you're a beginner, it's a good idea to seek the advice of a fitness trainer - whether it's a personal trainer or a trainer at your gym -- to be sure your form is safe and correct.