If you think you've got to spend hours at the gym, think again. David Kirsch's plank workout will help you shape up in a flash.

By Lynya Floyd

No time to work out? No problem. This routine will help you get in shape in just five minutes. "It's excuse-proof," says David Kirsch, a celebrity fitness and wellness expert and author of David Kirsch's Ultimate Family Wellness. "Everyone can spare five minutes in the morning to charge up for the day, recharge midday or decompress at the end of the day to connect your mind and body."

Since this is fast fitness, you'll want to keep your head in the game the whole time and pay attention to form. When you're in a plank psoition, make sure your spine is long, your core is tight and your glutes are flexed. You'll also need to be mindful of keeping your torso parallel to the floor. "Don't drop your hips and keep your shoulders relaxed," explains Kirsch, a popular personal trainer and single dad to two twin girls. "You shouldn't look up or down—just keep your head in a neutral position."

Worried this workout is too tough? Take it down a notch. Use a modified plank, holding the position on your forearms (if your wrists feel weak) or your knees (progressing to one knee and one straight leg when you get stronger). "If you get tired, rest on your knees or go up into a pike position," suggests Kirsch. Ready to break a fast sweat? Try this five-minute routine from Kirsch's book.

Move #1: Plank with Knee Tuck to Hip Abduction

1. Start in a plank position. Bring your right knee in toward your left shoulder, then extend your leg back and out to the side (i.e., hip abduction). That's one repetition. 2. Repeat 15 times with each leg.

Move #2: Plank with Dumbbell Row to Triceps Extension

1. Start in a plank position with a dumbbell (or water bottle) in your hand. 2. Pull up your right arm, keeping it close to your side and immediately extend your arm back to engage your triceps. Repeat 15 times on each side.

Move #3: Plank with Front Raise to Side Lateral

1. Start in a plank position with a dumbbell (or water bottle) in your hand. 2. Raise your right arm out to the side and parallel to the floor, then forward in front of your body. Repeat 15 times on each side.

Move #4: Side Plank Oblique Crunches

1. Position yourself in a side plank, resting on your right forearm, with your left arm behind your head. 2. Bring your left elbow in toward your belly, then return to the starting position. Do 15 repetitions on each side.

Move #5: Plank with Shoulder Taps

1. Start in a plank position. 2. Alternate tapping your hands to the opposite shoulder. Focus on keeping your core engaged and hips aligned, not wiggling.