“A complex is a group of exercises done using one piece of fitness equipment,” says NYC-based trainer Joe Dowdell - say, a barbell, dumbbells, kettlebells, or a suspension trainer. The movements are performed back to back, and you don’t rest until you’ve finished all your reps for every lift.

“Complexes are very time-efficient, and are great for fat loss,” says Dowdell, “because you perform a high volume of work in a short period of time - 15 to 30 minutes.”

Use this advice:

The Zero Time, Zero Space Barbell Complex

For this workout, perform each exercise in sequence. Complete six reps for each in turn, and then rest until your heart rate returns to 60 to 65 percent of its max (so wear a heart-rate monitor if you have one; if not, rest for 45 to 90 seconds). Repeat for four to five rounds. You can perform the workout three times per week on non-consecutive days.

This workout was written for use with a barbell, but you could do it with two dumbbells or kettlebells as well.

Hang Clean

Start by holding the bar in front of your thighs with your hands at shoulder width. Your feet should be hip-width apart. Bend your hips and knees so that the bar lowers to just above your knees. Your head, spine, and pelvis should be aligned and your core tight (think: ribs down).

Then, explosively extend your hips and knees as if jumping, while at the same time shrugging your shoulders and pulling the bar straight up in front of your torso. As the bar reaches chest level, bend your elbows and flip your wrists to catch the bar at shoulder level, palms facing the ceiling. Bend your hips and knees as you catch the bar to absorb the impact.

Front Squat

From the top position of your last hang clean, set your feet between hip- and shoulder-width apart, and turn your toes out slightly. Take a deep breath and squat as low as you can, while keeping your head, spine, and pelvis aligned. Keep your elbows pointing forward to balance the bar.

Push Press

From the top of your last front squat, dip your knees quickly and then come up explosively so that your legs help you press the bar overhead. Lower the bar to shoulder level again and repeat.

Bent-Over Row

After your last press, lower the bar to arm’s length again in front of your thighs. Take a deep breath, and bend your hips back, while keeping your head, spine, and pelvis aligned. Bend until your torso is nearly parallel to the floor (your knees can bend, too). Draw your shoulder blades together as you pull the bar to your belly button.

Romanian Deadlift

Lower the bar to arm’s length again, and pull it into your shins. Think “proud chest,” and maintain your tight core and the alignment between your head and hips. Squeeze your glutes to extend your hips, and come up to standing. From there, begin your next rep by bending your hips back and your knees, as necessary, until you feel a stretch in your hamstrings.

For a full compendium of fitness knowledge, check out the Men's Health Encyclopedia of Muscle. The volume is chock full of workout routines, helpful training tips, and definitions for just about every gym-related term you've ever wanted to know.