Think you don't have time to work out? A 30-minute workout could change your mind.

What if being too busy to work out was no longer an excuse? What if you could get an effective workout in 30 minutes a day? Think about it: 30 minutes. That's just half an episode of Gray's Anatomy. And an effective 30-minute workout is no pipe dream, says personal trainer Jonathan Ross.

"Everyone thinks that if they don't have an hour, than it's not worth it," says Ross, owner of Aion Fitness in Bowie, Md. "If you need an hour, think about how you feel at 59 minutes and 59 seconds. Then wait a second. Does something magical happen at 60 minutes?"

The answer, of course, is "no".

"Our bodies are responsive to exercise on a continuum, not on a time-based threshold," says Ross, the American Council on Exercise's 2006 Personal Trainer of the Year. "An effective workout can be had in any amount of time, given how you manipulate the variables of the workout."

Fitness expert Petra Kolber agrees.

"Doing something is better than doing nothing," says Kolber, a spokesman for the IDEA Health and Fitness Association and a contributing editor for Health magazine. "Thirty minutes is a realistic time frame for us to take out of our day to take care of ourselves."

What Makes Up a 30-Minute Workout?

To maximize the benefits, your 30-minute workout should consist of both resistance training and cardiovascular training, Ross says.

Ross likes to make a workout two-thirds resistance training and one-third cardiovascular training. In a 30-minute workout, that's 20 minutes of resistance and 10 minutes of cardio. Yes, just 10 minutes. But 10 strong minutes, he says.

"People don't need more time, they just need more intensity," he says. "The body responds more to intensity than it does to the duration of a workout."

A more intense workout burns more calories per minute, and will result in a much stronger post-exercise reaction, says Ross. In essence, he says, when you push the intensity, you traumatize the body (but in a good way).

"The metabolic system sends a message that it needs to make this person a lean, mean, fighting machine," he says.

For resistance training, Ross and Kolber say the important thing is to cover the whole body. Kolber opts for covering many major muscle groups at once, by combining lower- and upper-body exercises. Ross establishes an exercise "template" targeting specific types of movement so that he covers all the major muscle groups and can vary the actual exercises.

A 30-Minute Workout Program

Here is Ross' 30-minute workout template, with Kolber's suggested exercises included where appropriate. Remember that this list is not exhaustive. There are many exercises you can choose for each movement, as well as many versions of each exercise.

1. Lower-Body Exercise Targeting the Quadriceps.

Squats are the obvious example. Ross suggests a beginner version with the exercise ball: Stand against a wall with the ball at your low back, your feet hip-width apart and out in front of you. Slowly lower your body by folding at the hips and bending the knees, dropping glutes toward the floor.

To target more muscle groups in less time, Kolber does an overhead press while doing a squat. She notes that when doing two things at once, it's even more important to focus on good form and technique.

In this category, Kolber would also do a forward lunge: Standing with feet hip-width apart, take a big step forward with one leg. Then slowly lower the body toward the floor, front knee aligned with ankle, back knee pointing toward the floor. For more challenge, hold a free weight in both hands and complete the lunge with a rotation in the torso, twisting the body toward the forward leg.

2. Lower-Body Exercise Targeting the Hamstrings.

Ross suggests a dead lift: Holding a body bar or free weights and standing with feet hip-width apart, fold at your hips, moving the hips backward as you lower your upper body parallel to the floor. Keep the legs straight without locking the knees, and keep the back level and the spine in neutral.

The bridge is Kolber's option. This works the lower body, including the glutes and hamstrings, as well as the core. Lying on your back with knees bent and feet hip-width apart, slowly peel the spine off the floor, starting with the tailbone, until your body forms a diagonal line from knees to shoulders. While in this position, you can target the triceps: holding light weights, lift the arms toward the ceiling, then bend elbows toward your shoulders.

3. Upper-Body Horizontal Pushing Movement.

Push-ups are a great choice here, with many different variations depending on your strength. Ross recommends doing a push-up with an exercise ball under the hips, knees or feet as you lower and lift the body.

Kolber does a variation on a traditional push-up: From a face-down position on the floor, come to a plank position, supporting your weight on your toes and your extended arms. Lower your body down slowly, then bend your knees to the floor for a push-up.

A chest press is another example. Lying face-up on a bench with knees bent and spine in a neutral position, press a body bar or free weights from your chest up toward the ceiling. Fully extend arms without locking the elbows and move slowly in both directions, keeping shoulder blades on the bench. For an extra challenge, do the chest press with your head and upper back on an exercise ball.

4. Upper-Body Horizontal Pulling Movement.

If you have access to cable machines, this the best way to do an upright row. If not, try this free-weight version: Sitting straight with a neutral spine, lift weights up to shoulder height with straight arms. Then slowly bend the elbows and pull back, drawing the shoulder blades together.

5. Upper-Body Vertical Pushing Movement.

To do an overhead or shoulder press with free weights, begin with elbows bent and weights at shoulders. Slowly reach toward the ceiling, keeping the elbows under the hands and the shoulders away from the ears.

6. Upper-Body Vertical Pulling Movement.

This motion is best performed on a cable machine. Sitting straight with a neutral spine, slowly pull the bar down past the face and toward the chest. Only go as far as you can without leaning back, and control the weight on the way back up.

7. Core or Abdominal Exercise.

The choices here are almost endless. Ross suggests a slowed-down bicycle crunch: Lying on your back on the floor, fold knees in toward the chest and curl the upper body off the floor. With hands behind head, slowly rotate upper body to the right while drawing the right knee in and reaching the left leg out on an angle. Then rotate left and pull the left knee in. Focus on bringing the shoulder toward the hip (rather than the elbow to the knee), and try to keep the opposite shoulder off the floor.

Another alternative Ross likes is a side plank on the elbow. Lying on your side with a bent elbow directly under your shoulder, use your torso muscles to lift the body up into a side plank. Then lift the hips higher, then back to the plank, then lower. Do as many as you can with proper form, then repeat on the other side.

 By Barbara Russi Sarnataro