HOW TO DO IT

Perform 50 reps of each exercise in any order as quickly as you can without rest. You don’t have to do all 50 reps in a row—you might do 20 pushups, move on to jumping jacks, do another 15 pushups, and so on. Once you complete the circuit, rest 1 to 2 minutes and repeat. Do up to 3 circuits total, starting with a different move each time.

Time: 18 minutes
Equipment: None
Target: Total body
Calories burned: 248*
Trainer: David Jack, performance coach and owner of Actv8 Phoenix
Best for: Fitting in a quick, metabolism-revving workout when you’re on the road, pressed for time, or don’t have access to fitness equipment or a gym

*As measured by a fit 5’11” 175-pound man using a Polar FT7 watch

 PUSHUP

Drop down on all fours and place your hands on the floor so they’re straight and slightly beyond shoulder width. Lower your body until your chest nearly touches the floor, and then push yourself back up as quickly as you can.

 MOUNTAIN CLIMBER

Assume a pushup position with your arms straight. Lift your right foot off the floor and bring your knee as close to your chest as you can, touching the floor with your toes. Repeat with your left leg. Continue alternating back and forth.

 CRUNCH

Lie on your back with your knees bent and feet flat on the floor. Place your fingertips behind your ears. Now raise only your head and shoulders as you crunch your rib cage toward your pelvis. Return to the starting position and repeat quickly.

 JUMPING JACK

Stand with your feet together and hands at your sides. Now simultaneously swing your arms above your head and jump just high enough to spread your feet wide. Without pausing, quickly reverse the movement and repeat.

 BODY-WEIGHT SQUAT

Hold your arms straight out in front of you and stand as tall as you can with your feet shoulder-width apart. Push your hips back and lower your body until your thighs are parallel to the floor. Drive back up to the starting position and quickly repeat.