The amount of break time you take determines how your muscles adapt to the movement, says Carwyn Sharp, Ph.D., chief science officer for the National Strength and Conditioning Association. "Matching rest periods and intensities places the appropriate amount of stress on the muscles and their energy systems," he says.
Besides working your muscles in different ways, the breather you take between exercises correlates to injury prevention. "If you wait too long to move your muscles again, they become cold, which increases the risk of injury due to muscle damage," says Peter McCall, exercise physiologist and American Council on Exercise trainer. "On the other hand, if you don't rest long enough, your body can't replenish the muscles' energy efficiently, so you're exercising in a fatigued state. This can lead to poor form and therefore injury."
Reach your fitness goals while still feeling 100 percent by following this goal-based breakdown.
Editor's note: For much of the advice below, it's helpful to know your 1RM, or one rep max. That's the maximum amount of weight you can lift and perform one repetition before you're fatigued. If you aren't sure of your 1RM, here's how to calculate it.
If your goal is to get stronger, faster…
A recent study found that when performing a three-rep move (that means you'd be pumping heavy iron—85 percent or more of the max weight you can lift), you should rest a minimum of two minutes between sets. The Effect of Rest Interval Length on Repetition Consistency and Perceived Exertion During Near Maximal Loaded Bench Press Sets. Scudese E, Willardson JM, Simão R. Journal of strength and conditioning research / National Strength & Conditioning Association, 2015, undefined.;29(11):1533-4287. This will maximize your strength gains. Even better, waiting three minutes will help lower your perceived exertion levels or how hard you think you're working, while still boosting your stamina.
"The rest between sets determines your ability to sustain the heavy weight for subsequent sets," says Estevao Scudese, study author and associate researcher at Federal University of Rio de Janeiro in Brazil. Effect of different rest intervals, between sets, on muscle performance during leg press exercise, in trained older women. Filho JC, Gobbi LT, Gurjão AL. Journal of sports science & medicine, 2013, Mar.;12(1):1303-2968. This study also supports resting longer to lift more later.
Your muscles need this time to prepare for the next set of moves so the energy compounds, known as phosphagens, can replenish, says Amanda Butler, a certified trainer and instructor at The Fhitting Room in New York City. Without giving them the chance to refill, you’ll feel too fatigued too fast.
So what should you do during those minutes of rest? Sit and relax, especially if you focused on your legs. Another study found that rest intervals are particularly important when working major muscle groups, like those in your lower body. The effect of between-set rest intervals on the oxygen uptake during and after resistance exercise sessions performed with large- and small-muscle mass. Farinatti PT, Castinheiras Neto AG. Journal of strength and conditioning research / National Strength & Conditioning Association, 2012, Feb.;25(11):1533-4287. If you worked your shoulders, arms, or chest and prefer not to take a seat, Butler suggests walking around the room. Another option: Shake out your limbs to release any tension, and help keep yourself calm and loose between sets.
For those who just can't squeeze in the necessary wait time, try doing super sets. This involves alternating exercises that focus on different muscle groups, McCall explains. For example, do push-ups followed by deadlifts—the upper body can then rest while you work your lower half and vice versa.
One more note about lifting heavy weights: It's a great (safe!) idea to have a spotter. Whether that's a fellow lifter or a trainer, knowing a spotter is there can put you at ease mentally, allowing you to complete reps with better form.
Your Plan: Lift 85 percent or more of your 1RM, 1 to 6 reps, 2 to 6 sets, 2 to 5 minutes of rest
If your goal is to build more muscle...
To sculpt defined muscles and actually add mass to your body, you can slightly reduce your rest time. Just remember: "If you eliminate the rest period altogether, you change the physiological stress on the body, making it more of an endurance workout, which is not an effective way to build muscle," Sharp says.
Your Plan: Lift 70 to 85 percent of your 1RM, 6 to 12 reps, 3 to 6 sets, 30 to 90 seconds rest
If your goal is to drop pounds...
Fitting into a smaller pants size involves a combo of all of the above approaches, Sharp says. Eliminating rest periods and pushing through a 30-minute workout without stopping will certainly help you torch more calories, a key to losing weight—but that’s not the only factor.
"Maintaining or increasing muscle mass and strength are also important, because they allow your body to burn more calories while at rest," he explains. The more muscle you have, the higher your calorie burn throughout the day, even when you're sitting on the couch. If you're new to weight training, you can also try the plan below.
Your Plan: Lift lighter resistance, 8 to 15 reps, 1 to 2 sets, 30 to 90 seconds of rest
Of course any of these outcomes will improve your health—strength, muscle mass, endurance, and weight loss are all positive outcomes. So if you end up cutting your rest a little shorter or making it longer than planned, don't fret: You'll still gain benefits. Just keep in mind that the heavier the weight you're lifting, the longer you should wait to pick it back up.
Even more important: Listen to your body, says Butler. If you feel too tired or your heart rate is too high to start another round, give yourself a few extra seconds. If you're feeling strong and energized, make your rest time a little shorter that day.