Should You Increase Reps or Weight to Build Muscle and Strength?

Key Points:

A new study had 39 untrained young men and women train the leg extension twice per week for ten weeks.
With one leg, they progressed by increasing weight when they could do more than 12 reps. With the other leg, they stuck to the same training weight for ten weeks but progressed by doing more reps.
Gains in strength and muscle size was similar between the two legs, showing that beginners can achieve progressive overload with either method.

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In the field of strength training, progressive overload is king.

Challenge your muscles with something they haven’t done before, and they’ll respond by growing bigger and stronger.

In gym jargon, progressive overload refers to gradually increasing the stress on your muscles in order to keep the whole process of stimuli → adaptation going.

The three main (but not the only) ways to do this in your training is to increase either the:

Weight
Reps
Sets

But rarely do we see studies comparing these methods in order to glean which is better for building muscle and strength.

Until two weeks ago, that is.

Progress in Weight or Reps for Ten Weeks

A new study out of Brazil wanted to compare the effects of progressing through increased weight versus reps.¹

They had 39 previously untrained young men and women (50/50 split) train the leg extension for ten weeks.

One of each participant’s legs was assigned to a load progression group, and the other was assigned to a reps progression group.

Both legs started training with 80% of their 1RM in the one-sided leg extension (which was tested for each leg before and after the study), doing 4 sets x 9–12 reps per set.

But only the starting point was the same. They then followed two different progression methods:

The load progression group increased the weight (by a minimum of 1 kg) whenever they could do more than 12 reps in a set.
The reps progression group stayed with the same training weight for the entire ten weeks, but instead increased the number of reps they did per set.

To summarize: every participant was in both groups. One leg in the load progression group, and one leg in the reps progression group.

This is called a within-subjects design, and it has many benefits. First of all: you immediately double your number of subjects, with 39 participants turning into 78 legs. Secondly, you get way less variability between subjects because you have “pairs” with identical energy intake, training history, sleep, and genetics. However, it also has drawbacks, which I’ll get back to later.

Every participant did 23 workouts over the ten weeks of training, averaging out to 2.3 workouts per week. In each workout, they did four sets until failure per leg, each leg progressing according to their designated group. One group (or leg) increased the weight whenever they did more than 12 reps per set, while the other stuck with the same weight and just tried to do more reps.

Before and after the study, they tested each leg’s 1RM in the one-sided leg extension and measured the cross-sectional area of their vastus lateralis (the biggest quadriceps muscle) at the midpoint of their thigh.

Leg Extension exercise — The leg extension exercise. However, in this study, they trained and tested it with one leg at a time.

The Results

When they tested strength and measured muscle growth after the end of the ten weeks, they found no significant differences between groups.

On average, both legs had gained similar amounts of muscle and strength without so much as a hint of a difference.

As much as the training differed between groups in this study, both protocols seemed to work splendidly for beginners going through their first ten weeks of training.

But it begs the question …

How Much Did The Training Really Differ?

Both legs started their training at 80% of each respective leg’s 1RM in the leg extension, with the aim of doing 9–12 reps per set for four sets per workout. Each set was taken to failure.

So, in the beginning, we can assume that the training for both legs was virtually identical.

The load progression group started their training with a mean training weight of 42.3 kg, and finished with a mean training weight of 61.4 kg after ten weeks. They were still doing 9–12 reps per set.
The reps progression group started their training with a mean training weight of 41.6 kg and used the same training weight for the entire training period. They did 9–12 reps per set in the beginning, but how many reps were they doing per set towards the end of the study?

Because the authors of the study have supplied the mean volume load (weight x reps x sets) for every workout and we know the weight used as well as the number of sets, we can do some rough estimations.

Progressive overload with reps or weight — Volume load per session (weight x reps x sets). Notice how close in volume the two groups are! I don’t think I would have guessed that.

Just by a rough approximation from the graph, we can see that the reps progression group’s mean volume load in their last workout was ~2550 kg. Divide that by their training weight (41.6 kg) and the number of sets (four), and we get 15.3 reps as an average across the four sets.

Because rep numbers tend to drop off steeply during a set when you are training to failure (and with only 90 seconds of rest between sets in this case), I am guessing that they probably got closer to 20 reps in their first set, and fell down towards 10 reps or so in their fourth set.

If we do the same math but for the load progression group, we get an average of 10.4 reps per set in their last workout.

So how different is this?

Not very.

4 sets x 10 reps to failure compared to 4 sets x 15 reps to failure (on average) are fairly close to each other in the grand scheme of strength training.

If anything, the relative weight they used differed more.

The load progression group finished their workouts with a training weight of 88% of their new 1RM (the one they achieved after the training period), and the reps progression group trained with what, at the end of the ten weeks, was 62% of their new 1RM.

If you check out our article on how many reps to build muscle, you’ll see that muscle growth is actually pretty similar across a wide range of reps and loads, provided that you train close to failure.

Anything between roughly 5–30 reps per set and about 40–85% of 1RM has been shown to be effective in building muscle. More or fewer reps than that, and the muscle-building effect per set decreases somewhat.

Therefore, we shouldn’t really expect too big differences in results in the type of comparison done in this study.

What it does show, however, is that you can get great results as a beginner by adding weight and by adding reps. You’re free to choose!

The Cross-Education Effect

I mentioned earlier that the within-subjects design used in this study (each participant being a member of both groups) has many benefits but also some drawbacks.

One drawback that becomes a confounder in a study like this happens because of the cross-education effect.

The cross-education effect is the phenomenon where we train one arm or leg, but both sides increase in strength.²

It is thought to happen because we gain neuromuscular skill or efficiency that applies to both sides of our bodies, even though we only trained one.

What it means for the results of this study, however, is that cross-education between the two legs might have skewed the results: If one leg trains with heavier weights, that skill and improved motor function might affect the strength gains of the side training with lighter weights.

In this particular study, the endpoints in terms of reps per set weren’t very far off from each other, so I don’t think it is too much of an issue. (Although I’m a bit surprised the authors didn’t even mention it in their article.)

But still, it makes me a bit curious whether or not we would see any differences in a traditional between-subjects design, where one participant belongs to only one group.

Practical Take-Away

Whether you should progress your training by increasing weight or reps is one of the fundamental questions of strength training, and I enjoyed this study both from a theoretical and practical perspective.

Because the study “only” (Hey, I am grateful for what we get in this field. No hate on the researchers, who did an awesome job.) lasted for ten weeks, the two groups didn’t have time to diverge that much from each other, so we can’t glean too much from this. I’d love to see what would happen if they kept this up for a year, but that is a pipe dream.

From a more practical standpoint, this shows that a beginner going through their first few months of strength training can get great results in terms of both strength and muscle growth by using either method:

Either increase the weight and stick with the same number of reps, or
Stick with the weight but increase the number of reps.

The latter requires that the weight was heavy enough to begin with, though.

Double-Dip With Double Progression

Probably the most common progression method is to use a little bit of both:

Increase the number of reps you can do with a given weight until you start to get out of the rep interval you want to stay in,
Then increase the weight, which will lower your reps per set again.
Repeat.

This is probably one of the more intuitive ways to progress once you’ve learned the ropes in the gym.

An alternative approach is to alternate between the two methods:

Progress only in reps with the same weight for four to six weeks,
Switch and progress in weight (keeping the number of reps the same) for another four to six weeks.

Periodization, baby.

The big idea is that as long as you progress your strength training in some manner, gains will follow.

What is the best way to keep track of your workouts so that you know you’re progressing?

With the StrengthLog workout app, buddy.

Download StrengthLog for free with the links below: