Timers are a convenient way
to keep track of rest breaks.

Exercise is all about controlling the variables. Deciding how intense a workout should be, how many sets you should do and the number of reps that are appropriate. One thing that's often ignored is how long you should rest between sets.

Take too short of a break and your muscles quickly fatigue. Take too long and your body starts to cool down. For optimum results, the timing has to be just right. To figure it out, we decided to see what the studies said.

We were in luck. Researchers at the Laboratory for Clinical and Experimental Research in Vascular Biology at the State University of Rio de Janeiro did all the hard work. They published a paper called, "Rest interval between sets in strength training." In it, they looked through dozens of original scientific investigations and narrowed it down to 35 studies. They focused on rest intervals between sets and how those breaks targeted specific training outcomes. This is what they found.

Rest intervals between sets can be separated into three groups based on the desired outcome. The first is an increase in absolute muscular strength, the second is building the greatest muscle mass and the last is for endurance.

If your goal is the greatest strength (muscular power) or the most repetitions over multiple sets, you should let your body rest 3-5 minutes between sets. That's also the ideal break when you're working with really heavy loads, between 50% and 90% of your one-repetition maximum. (For those of you who don't know, your one-rep max is: The maximum amount of weight you can theoretically move for one repetition while maintaining good form.)

Resting for 3-5 minutes allowed the greatest amount of muscle recovery so the intensity and volume of training could be increased.

When the goal is muscular hypertrophy (building bigger muscles) the studies recommended moderately intense sets and shorter rest intervals of 30-60 seconds. It was more effective because that's the pace where the most acute levels of growth hormone were produced.

The results for endurance training weren't quite as clear. The commonly accepted wisdom is that rest periods of 20-30 seconds are perfect for endurance. The studies confirmed that 20 seconds on the low end can be appropriate, but anything between 20 and 60 seconds can help build "higher repetition velocities."

In other words, the ideal rest period for building endurance is nearly the same as for building bigger muscles. You'll have to judge for yourself based on how you feel. If you can comfortably start after a 20-second breather, go for it. But don't feel bad if you need the full 60 seconds to recover.

Here's what that means when you design your workouts.

If you're trying to build endurance for long-distance events like running, jogging, biking or cross country skiing, take the shortest break you reasonably can. Just make sure it's at least 20 seconds but don't rest for longer than a minute.

For those of you trying to build the biggest muscles, 30 seconds is the shortest your break should be, but don't sit around for more than a minute. Only extend it beyond if you're trying to recuperate from something that's particularly strenuous or a superset.

When ultimate strength is the goal, you get to relax. You can give your muscles a full 3-5 minutes to recuperate between sets. When you do your lifts, your program should be moving heavy weights with low repetitions.

Don't guess how long you're resting. Get a stopwatch or use a kitchen timer. You might even consider one of the custom timers built just for working out.

When used appropriately with other parts of a well-designed program, the rest periods between sets can make all the difference between a good and a great workout. They influence the efficiency, safety and ultimately how effective a training program will be.

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10/3/2010