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Don't do more than a total of 22 good sets in a workout if you're looking to bulk up, says Rooney. Also, limit yourself to four sets per exercise. Researchers in Australia found that more than four sets offers diminishing returns.
OLD WAY: Always Lift Heavy
NEW WAY: Go Light to Grow big
"High weight, low reps" is the classic mantra of men who are trying to pack on size and strength. But a new study in the Journal of Applied Physiology found that lifting lighter weights for more reps—three sets of up to 30—can boost growth as much as lifting heavy weights in the 8-to 12-rep range. "As long as your muscles reach fatigue, they'll grow," says John Romaniello, N.S.C.A.C.P.T., owner of Roman Fitness Systems. "And some muscles, like those in your lower body, respond better to high reps."
More: The Ultimate Fitness Formula
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Do "breathing reps" for several of your lifts: Load a bar with a weight you can squat, press, or lift 12 to 15 times, and do those reps. Without letting go of the bar, set it down, take two breaths, and do 1 or 2 more repetitions. Continue the process until you reach 20 reps. That's 1 set; do 3. "Including both highland low-rep sets in your workouts ensures that you're hitting both your fast-and your slow-twitch muscle fibers," says Romaniello.
OLD WAY: Hoist More Weight
NEW WAY: Haul More Weight
Most men are accustomed to lifting, pushing, and pressing heavy loads. But when asked to carry one—whether it's a sandbag, kettlebell, or air conditioner—many become a stumbling mess after a few paces. That's because "loaded carries" simultaneously test your stability, mobility, balance, and grip while keeping your muscles under constant tension. "They challenge your entire body, especially your lateral core strength, which is critical for everything from fast cuts to powerful serves," says Stuart McGill, Ph.D., author of the seminal study on the subject, published in the Journal of Strength and Conditioning Research.
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Add the suitcase carry to your next workout. Grab a heavy kettlebell or dumbbell (45 pounds is a good starting weight) and walk forward and backward for 30 to 75 seconds. "The asymmetrical load works your obliques—which are important for lateral core strength—as well as your glutes, which are essential for athletic power," says McGill.
More: 8 Fat Burning Kettle Bell Moves
OLD WAY: Watch the Clock
NEW WAY: Personalize your Rest
Trainers know that exercise affects everyone differently, and Brazilian researchers recently confirmed that notion when they found that people differ significantly in their recovery needs. And without proper recovery, performance suffers, especially if you're doing circuits. "Use a heart rate monitor to customize your rest," says Rachel Cosgrove, co-owner of Results Fitness in California. "Waiting until your heart rate reaches a certain level results in true recovery between work periods, which is particularly beneficial for losing weight."
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Determine your maximum heart rate: Multiply your age by 0.7 and then subtract that number from 207. Then strap on a heart rate monitor and track your pulse between circuits. When it drops to 75 percent of your maximum, begin your next one. "Your rest periods will become longer the farther you get into your workout," says Cosgrove. "But your form—and performance—should be better throughout."
More: Calculate Your Training Heart Rate Zones
Stay in shape in a fitness class.