Higher Reps for Mass: Why High Reps Build Muscle

If you want to build muscle mass, should you be training with heavy weights and low reps? Or will lighter sets and higher reps do a better job?

To answer that question, a team of US researchers set up a very simple experiment  [1]. They took a group of guys who’d been lifting weights for at least a year, and split them into two groups.

Both groups followed the same training program – bench press, military press, wide grip lat pulldown, seated cable row, squat, leg press and leg extension – three times per week for eight weeks, but with one key difference.

High Reps vs Low Reps for Muscle Growth

Group one did 3 sets of 8-12 reps to failure with a heavy(ish) weight. Group two, on the other hand, trained with higher reps and did 3 sets of 25-35 reps to failure.

All other variables – rep tempo and rest between sets – were kept the same.

Which group do you think built the most muscle?

Conventional wisdom says that the group lifting the heavier weights would build the most muscle, while those training with higher reps would gain some size and strength, but to a much smaller degree.

But that wasn’t the case.

Why High Reps Build Muscle

In fact, the results show no difference in the rate of muscle growth between the two groups.

Training with higher reps and lighter weights led to gains in muscle size that were on par with heavier training.

It was a different story where strength and endurance were concerned – guys training with the heavier weights saw the greatest gains in strength, while those doing higher reps saw the biggest change in muscular endurance.

One potential explanation for the muscle growth seen in the group training with higher reps is an increase in the size of the type I muscle fibers, although this wasn’t actally measured in the study.

Given that type I muscle fibers are highly resistant to fatigue, the increase in time under tension associated with low-load training may have stimulated growth in fibers that were relatively underdeveloped compared to their type II counterparts.

To quote the researchers directly:

“None of the subjects in our study reported training with more than 15 repetitions per set as part of their normal resistance-training programs. Thus, it is possible that the type I fibers of subjects were underdeveloped in comparison to the type II fibers as a result of training methodologies. The type I fibers therefore may have had a greater potential for growth compared to the type II fibers, and the extended duration of the low-load sets conceivably provided a novel stimulus to promote greater growth in the endurance-oriented type I fibers.”

As with any study, there are a few limitations to consider.

Firstly, muscle growth was measured only in three locations (biceps, triceps and quadriceps femoris). The results may have been different had other muscle groups been included in the analysis.

Second, the study lasted only eight weeks. This was long enough to produce significant gains in muscular strength and size. But we don’t know how things would have panned out had the study lasted longer.

Should You Use Higher Reps for Mass?

What’s more, the fact that it’s possible to build muscle using higher reps and lighter weights doesn’t necessarily mean that it’s a good idea to do so.

Remember, 3 sets of 25-35 reps was no better than 3 sets of 8-12 reps for building muscle. But each set took around three times longer to complete.

Training to failure in a higher rep range is also highly unpleasant and extremely painful – a lot harder than lower reps and heavy sets.

Doing longer, more painful workouts simply to generate the same results doesn’t sound like a great idea to me.

While this study shouldn’t be interpreted to mean that training with higher reps and lighter weights is a better way to build muscle than lower reps and heavy weights , it does show that the range of repetitions you can use to add mass is a lot wider than previously thought.