The more intensely you train (without working above 85 percent of your maximum heart rate), the less time you'll need to exercise to get the same results. Walking, jogging, swimming, bicycling are all good fat-burning exercises when done at your target heart rate.

Similarly, the point of strength or resistance training "isn't necessarily how many sets you do, or how often you lift," says Stefano, "but how intensely you train while adhering to perfect form. This intensity level is relative, varies with each individual, and depends on many factors, including age, sex, and current level of fitness."

Stefano says the top resistance exercises for improving muscle tone are the captain's chair for abdominals, squats for the buttocks and push-ups for the arms, shoulders and chest.

The "Interval" Workout
Greg Florez, spokesperson for the American Council on Exercise and chief executive of FitAdvisor.com, agrees with Stefano that you can accomplish a total body-conditioning workout in 30-45 minutes. "The key issues are working large body parts in a strength program and getting the correct intensity in both the cardiovascular and strength training portions," he says.

To do this, add a strength exercise approximately every two to three minutes to your cardiovascular workout. In other words, stop jogging, stair climbing or doing the elliptical trainer and hit the mat to perform 12-15 push-ups. Then immediately resume your cardiovascular exercise without rest. Continue doing intervals throughout the cardio routine to work your way through the major muscle groups in your body — shoulders, back, chest, arms, hips/buttocks and legs.

Intervals Increase Caloric Burn and Fitness
Interval training can help break up the monotony of jogging on a treadmill for 30 minutes, but more importantly, it can help you maintain a relatively high level of intensity, which increases the number of calories burned and helps to build your overall fitness level. "That is why interval training is so valuable," says Florez, who suggests doing one such workout each week as well as varying your normal cardio routine to add a bit of speed, incline or distance. Perform your cardio workout three to five times a week at a minimum of 20 minutes per session.

Quality is the goal when doing the strength portion of the workout. The 12-15 repetitions should be hard enough that you could not complete any more without compromising form and correct posture. When you pass that level, you should increase the weight/resistance.