Styling by Justin Berkowitz. Grooming by Anna Bernabe/Exclusive Artists/Oribe. Casting by Edward Kim at The Edit Desk. Shorts by Vince. Sneakers and socks by Nike.

Leave puffy bubble butts to 'roid-heads and pancake-flat posteriors to middle-aged men in ill-fitting chinos: The ideal rear view is muscular, shapely, and strong—and essential to your total-body-workout results. "Much of your power and strength comes from the biggest muscle group in your body, your glutes," says celebrity trainer and strength and conditioning coach Michelle Lovitt, who has worked with clients such as Jason Statham, Kiefer Sutherland, and Gabriel Aubry. "But if you can't fire those muscles while you're working out, then you're likely to overuse your hamstrings and hip flexors instead, which can compromise your results and lead to injury."

Perform two sets of this three-move routine as a warm-up to your usual cardio workout three times a week. For a supercharged ass-kicking, try 30 to 60 minutes of cardio in the form of hill sprints (go full speed up a short incline, use the jog/walk back downhill as your recovery period, and repeat), says Lovitt. "By working your glutes from every angle, this routine will make you stronger, and help shape a better-looking booty, in a shorter amount of time." Get the picture? There's no excuse for dragging ass.

KNEELING GLUTE KICKBACK (pictured, top)

Start on all fours, with hands under shoulders, knees under hips, a resistance band wrapped around the bottom of your left foot, holding the ends of the band under each hand. Lift your left leg up behind you, with knee bent so your calf is perpendicular to the floor, hamstring in line with hips. Extend your leg behind you, and then bring your bent knee in toward your chest. Squeeze your glutes and push-kick your leg back behind you, keeping your foot flexed (as shown). Do 15 reps; switch legs and repeat.

Styling by Justin Berkowitz. Grooming by Anna Bernabe/Exclusive Artists/Oribe. Casting by Edward Kim at The Edit Desk. Shorts by Vince. Sneakers and socks by Nike.

SQUAT WITH SIDE LEG RAISE

Stand on top of a resistance band, with feet shoulder-width apart, holding the ends of the band so it crisscrosses in front of you (as shown). Squat, keeping your elbows bent by your sides, bending both knees 90 degrees. As you rise up out of the squat, lift your left leg up and out to the side, pushing against the band (as shown). Squat again, this time lifting your right leg as you stand up. Alternate sides for 15 to 20 reps.

SINGLE-LEG BRIDGE

Lie face-up, with knees bent and feet flat on the floor, hip-width apart, arms by sides. Wrap a resistance band around the bottom of your right foot, holding one end of the band in each hand, and extend your right leg toward the ceiling. Slowly lift your hips, pressing your right leg toward the ceiling, until you've created a diagonal line from the top of your left knee to your shoulders (as shown). Hold for a few seconds, contracting your glutes, then slowly return to start. Do 15 reps; switch legs and repeat.