Pumping iron is only part of the muscle-building formula. "Recovery is just as important," says Todd Durkin, C.S.C.S., author of The IMPACT! Body Plan. That's because weightlifting creates microtears in your muscles, and hitting the gym again too hard too soon can undermine the repair process (also known as muscle growth). "Your body needs at least one day of rest between workouts," says Durkin. Follow his four tips to make the most of your downtime. (Get more fast fitness fixes -- sign up for our free Exercise of the Week newsletter.)

Feed Your Muscles
Lifting weights makes your metabolism race as your body works to replenish energy and repair muscle tissue. "If you don't take in enough calories and protein, you won't have the resources you need to recover," says Durkin. He recommends consuming 300 to 500 additional calories on workout days, and skewing those calories toward protein, the building block of muscle. "Shoot for 1 gram per pound of body weight," says Durkin. (Do you really need to eat protein within 15 minutes of working out? Discover The Truth about Protein.)

Roll With It
Here's why you need a regular massage, or at least a foam roller: "Both can help break up the scar tissue that's a natural consequence of lifting," says Durkin. That not only speeds the repair process and reduces soreness but also improves range of motion, reports a study in the Journal of Strength and Conditioning Research. "Spend 5 minutes using a foam roller on your quads, hams, glutes, hips, and lower back before a workout and before bed," Durkin says. "If you can, also visit a massage therapist twice a month." (Foam rolling is an easy -- and cheap -- way to keep your body moving like a well-oiled machine. Check out The Best Injury-Prevention Workout You're Not Doing.)

Catch More Z’s
Muscle building doesn't shut down when you hit the sack. "Your body repairs a lot of damage as you sleep, so it's critical to get as much as you can," Durkin says. Indeed, a lack of shut-eye can increase muscle loss by up to 60 percent, according to researchers in Brazil. The reason: Your body produces its greatest surge of growth hormone while you're sleeping. What's more, the fatigue that goes hand in hand with too little sleep can torpedo your workout performance. Your goal: 7 to 8 hours of quality slumber every night. (Snooze soundly through the evening with these 6 Foods for Better Sleep.)

Take a Cold One
Tough workouts don't have to result in aching muscles. Immersing yourself in cold water immediately after intense exercise can reduce delayed-onset muscle soreness (DOMS) by nearly half, say scientists in Ireland. That means a faster return to peak performance and a lower likelihood of missing your next workout. Do this: Fill your bathtub with 50- to 59-degree Fahrenheit water (cool tap water is usually cold enough) and soak in it for 5 to 12 minutes in order to reduce the inflammation that causes DOMS, the scientists recommend.
Transform your body into a fat-burning machine with these 5 Easy Ways to Rev Your Metabolism.

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