The fastest way to develop a lean, muscular physique is through a method of training known as circuit training. Circuit training combines the best of both worlds: cardio and strength training. You move from one exercise to the next as quickly as you can without any rest, so your heart rate stays elevated. Once you have completed each exercise, you have gone through one circuit. You then repeat the circuit three to five times. By doing this you burn lots of calories and fat but also build muscle. It is the method of training the actors in the movie "300" used to get buff quickly.

Pullups

Perform as many bodyweight pullups as you can. If you can do more than 12 pullups in a row, you should add weight to your body with a vest or backpack. Each time you repeat the circuit, alternate your grip for muscle confusion, such as wide grip, narrow grip and neutral grip.

Dumbbell Bent Over Row

Perform 25 dumbbell bent over rows. Stand with your feet shoulder-width apart and a dumbbell in each hand. Bend over, keeping your back straight, and pull the dumbbells toward you in a rowing motion. Use a weight that you can easily perform 25 repetitions with. Remember, each time you repeat the circuit the exercise will become more difficult, so if you start out too heavy, you won't be able to complete 25 repetitions the next time around.

Pushups

Do as many pushups as you can. Alternate between narrow, neutral and wide pushups each time you repeat the circuit.

Jumping Jacks

Do as many jumping jacks as fast as you can with good form for one minute. Your finger tips must touch every time you bring your arms over your head.

Dumbbell Clean and Press

This is a compound exercise that will get your blood pumping fast because you are using your legs and arms in one movement. By this time in the circuit, your heart should be beating fast and your arms will start to feel tired, so don't worry about using a heavy weight -- 10 to 15-lb. dumbbells should be sufficient. Squat down low and pickup the dumbbells, pushing up with your legs through your heels. Bring the dumbbells up to your shoulders, then push your arms up over your head. Perform 25 repetitions as quickly as you can with good form. If this exercise is too hard for you at first, do a reverse bicep curl with shoulder press, which is the same exercise minus the squat.

Squat Thrusts

Perform 10 squat thrusts as quickly as you can. If you want to make this exercise more challenging, you can do a pushup each time you go down and a light jump each time you come back up to your feet.

Jumping Squats

Perform 10 jumping squats as quickly as you can. Squat down low so your thighs are parallel to the ground. Keep your heels flat on the ground and don't let your knees extend past your toes. When you are at the lowest point of the squat, quickly spring up into the air as high as you can. Land with soft knees and repeat.

Deep Squat

Hold a deep squat for 30 seconds. Keeping your heels flat on the ground, squat down as low as you possibly can, and hold the pose. Breathe while you hold the squat and slowly exhale as you come up. Form is important. Do not allow the knees to be forward of the toes in the squat. The squat is not performed straight down, but rather with the posterior region shifted to the rear somewhat, as if about to sit down.

Workout Schedule and Tips

Repeat the circuit as many times as you can in 30 minutes. Rest for 30 to 60 seconds after each circuit. Warmup before you start by jogging lightly for five to 10 minutes. Cool down afterward by doing some slow abdominal crunches and light stretching. Perform this workout three times per week with at least one day of rest in between. For optimum results incorporate as much muscle confusion as you can into the routine by alternating grips, stances and weight. For example, after you have gotten used to the circuit, do one day where you focus on maximum repetitions, then do another day where you focus on maximum weight -- this will keep your muscles guessing.