Weight training do's and don't's: How long should you rest between sets to build muscle?

Questions I get from readers are often highly insightful and demonstrate critical thinking about a variety of health issues. A recent letter from a reader asked a question regarding the optimal amount of rest between sets during a resistance training workout.

When you perform a resistance exercise (like bench presses or curls) ten times, that's ten repetitions (tenreps) and it equals one set. Following completion of the set, you rest to recover and prepare for the second set, then the third, and so on, until you move on to the next exercise.

Keep in mind that each set of ten reps should exhaust the working muscles. This means, even if highly motivated, you cannot do 11 reps without cheating, and you don't want to cheat because it can cause injury. If you can do more than ten reps in a set, but you stop at ten, the muscle has not reached full fatigue and the benefits are greatly reduced.

The reader pointed out that if he rests longer between sets, he is able to perform more reps on subsequent sets. In other words, he is able to do ten reps on the first set and if he rests for 2 minutes or more, he is able to do ten reps on the second, third and fourth sets. However, if he shortens the rest interval to only 1 minute or less, he does fewer reps on the second set, perhaps only seven, and even fewer on the third and fourth sets.

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His question is, in order to maximize strength gains, should he keep the rest interval longer between sets to get as many reps as possible on each set? Here's what to know.

How resistance training builds muscle

The key to success in resistance training is overloading the working muscles. You must force them out of their comfort zone, and the more you overload the muscles, the more you force them to make internal adjustments to get stronger. This is because muscles don't like to be overloaded, and they hope that if they adjust and become stronger, when you tax them again, it won't be as stressful. This is why you must continually add resistance in order to stay ahead of the muscles and keep forcing them to adjust to increasing demands.

With this in mind, there are many ways you can overload muscles. When you shorten the rest interval between sets, you are not allowing the muscles to recover completely before overloading them again on the next set. This results in fewer reps, but it's still a good dose of overloading. The same is true when you rest longer and get more reps.

Either way, when you get to that last rep, whether it be the tenth rep or the sixth, if you can’t do anymore, you know you have exhausted the muscle, overloading it adequately and forcing it to make adjustments.

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How blood flows to muscles during exercise

One way to assess the success of exercising a muscle is the amount to which the muscle is "pumped up," or gorged with blood. The scientific term for this is reactive hyperemia.

When you contract a muscle vigorously with at least 60% of its maximal capacity (if 100 pounds is a max one-rep effort, then working out with 60 pounds for tenreps would be 60% of max), the bulging muscle presses against the artery that feeds the muscle, shutting down blood flow into the muscle. This continues as long as the contractions (reps) continue. At the same time the muscle is working but without blood flow. This greatly increases the demand for blood flow in the working muscle, but that demand cannot be met until exercise stops.

When the set is completed, blood surges into the muscle, "pumping it up." Since this happens "after" the exercise is completed, it is "reactive," and hyperemia means excessive blood flow.

Here's what one study found about resistance training

Jordan Kuerzi, a student in my Kinesiology & Integrative Physiology Department at Hanover College is currently working on this issue as part of her senior thesis. Specifically, she is measuring the degree of reactive hyperemia with the standard four sets of ten reps in the dumbbell curl (2 minutes rest between sets) and comparing it with the same four sets completed with only 20 seconds between sets.

Thus far she has found that on the standard approach, subjects were able to complete approximately 40 reps (four sets of ten reps) owing to the longer recovery time. However, with an abbreviated time of only 20 seconds between sets, the number of reps falls off substantially in each successive set (for example, ten reps, then six, four, and three). In her study, each workout was separated by several days to ensure total recovery.

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Upon completion of each workout, the degree of reactive hyperemia was determined with the Archimedes Principle (the volume of an object is equal to the amount of water it displaces when submerged). When the arm is submerged in a plexiglass water tank, more reactive hyperemia results in greater water displacement, meaning greater arm volume. Although nearly twice as much work was accomplished with a much longer recovery time of 2 minutes between sets, the degree of reactive hyperemia was the same for both workouts.

Her study is still ongoing, but thus far it would appear the amount of time between sets is not relevant when seeking to make the muscle bigger and stronger as long as the muscle is pushed to full fatigue.

An advantage to the minimal rest between sets approach is that it greatly reduces the length of a workout. If you rest 2 minutes between sets and a set takes 1 minute, that means you are exercising only one-third of the time. In other words, if you spend an hour in the gym, you are exercising for only 20 minutes. A much shorter interval between sets reduces the time and gets you out of the gym faster, but without a reduction in benefits.

Reach Bryant Stamford, a professor of kinesiology and integrative physiology at Hanover College, at stamford@hanover.edu.

This article originally appeared on Louisville Courier Journal: How long should you rest between weight training sets to build muscle?