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With the exception of people named Bruce Banner, muscles need a certain amount of rest in order to strengthen and grow. But while some sources suggest muscles need 48 hours or more to recover from exercise, there might not be a one-size-fits-all timeline.

All Pain, No Gain: Why It Matters

Whether they’re in it for health, happiness, or an upcoming vacation, many gym-goers want to look and feel a certain way—and fast. But in the process of strengthening the legs, chest, or any other muscle group, rest is just as important as reps. And for many individuals, not taking an occasional rest day could lead to overtraining, which can mean decreased performance, elevated blood pressure, decreased immunity, disturbed sleep, and more.

Physical exercise, from lifting weights to running intervals, damages muscle fibers, and can create a feeling of soreness (and dread at the sight of stairs). But during rest periods, muscles have time to reconstruct (or recover) in stronger formations and increase in size. Yep, turns out that strength and muscle gains actually occur outside the gym, during periods of rest, not inside the weight room.

Some research suggests that because muscle soreness can peak two days post-exercise, a minimum of 48 hours of rest is optimal to allow recovery and prevent injury—at least among the competitive athletes who were studied.The effects of exercise-induced muscle damage on cycling time-trial performance. Burt DG, Twist C. Journal of Strength and Conditioning Research / National Strength & Conditioning Association, 2011, Dec.;25(8):1533-4287. Other experts suggest resting up to 72 hours between workouts if you're an exercise newbie, while some say eight hours of good sleep is enough for your body to recover.

Finally, one meta-analysis determined that for optimal strength development, one to two rest days between sessions is ideal for beginners training three days per week and experienced exercisers training two days per week.A meta-analysis to determine the dose response for strength development. Rhea MR, Alvar BA, Burkett LN. Medicine and Science in Sports and Exercise, 2003, Jul.;35(3):0195-9131.

Still, there are other factors to consider when it comes to determining adequate rest. Those who are older, for instance, may experience slowed muscle recovery and growth. Other factors include how intensely you work out, how often you work out, what you eat, and the duration of exercise. With so many mixed messages out there, one thing's for sure: Some amount of rest in your exercise routine is crucial to enhance muscle growth, and to keep symptoms of overtraining at bay.

Keep on Pushin’?

Young Man Stretching Still, your muscles may not need to take a total break from movement in order to fully recover. One study found low-intensity post-workout exercise—such as swimming laps or taking a walk—can increase muscle relaxation, which benefits recovery.Effect of incorporating low intensity exercise into the recovery period after a rugby match. Suzuki M, Umeda T, Nakaji S. British Journal of Sports Medicine, 2005, Feb.;38(4):1473-0480. Other research suggests muscles can work to full capacity even while in the recovery stage.Muscle damage and muscle remodeling: no pain, no gain? Flann KL, LaStayo PC, McClain DA. The Journal of Experimental Biology, 2011, Jun.;214(Pt 4):1477-9145. Plyometric exercise increases serum indices of muscle damage and collagen breakdown. Tofas T, Jamurtas AZ, Fatouros I. Journal of Strength and Conditioning Research / National Strength & Conditioning Association, 2008, Sep.;22(2):1533-4287. And keep in mind that "recovery" doesn't necessarily mean sitting on your couch all day either: Yoga, Pilates, light jogging, or swimming can be considered "rest day" activities, depending on your fitness level.

You can also look to more mellow treatments to speed recovery, including icing, heating, static stretching, and massage therapy.Manual therapy ameliorates delayed-onset muscle soreness and alters muscle metabolites in rats. Urakawa S, Takamoto K, Nakamura T. Physiological Reports, 2015, Feb.;3(2):2051-817X. (Don't forget about the trusty foam roller!) Another way to speed recovery: Pay attention to proper post-workout nutrition, including adequate amounts of protein.Postexercise muscle glycogen recovery enhanced with a carbohydrate-protein supplement. Berardi JM, Price TB, Noreen EE. Medicine and Science in Sports and Exercise, 2006, Oct.;38(6):0195-9131.

The bottom line: There’s no magic formula for optimal days of rest. Take your fitness level, intensity, frequency, and duration of activity into account, and look for signs that the body needs a break, like chronic muscle or joint soreness and impaired physical performance. Be sure to recognize the difference between pain and soreness, and most of all, don’t be afraid to take some time off.

Originally published November 2011. Updated June 2015.

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