People hire trainers for lots of reasons, but your success will always come down to muscle. Are your clients stronger? Are they leaner? Do they have more energy and less pain? Do they move faster, and feel better doing it? Every one of those outcomes is a function of muscle quality, and to achieve it, you’ll need to make the clients’ muscles bigger.

Few clients will come right out and say they want bigger muscles. But nobody ever complains when they get them. They like their new appearance, they like the way their clothes fit, and they especially like the compliments that come along with those results.

For me, building muscle has been a lifelong quest—not just lifting, but making a career out of studying and writing about every aspect of the process. One side effect of learning so much about a single topic is that you realize how hard it is for everyone else to stay current.

Human physiology hasn’t changed, of course. The basics you learned about muscle hypertrophy still apply. But in recent years we’ve seen an increasing divergence in how those basics are applied, with different camps staking out territory based on either research or experience.

The most important question isn’t who’s right, but how to use the best evidence we have to get the best possible results for your clients.

Consider this your refresher course on the science and practice of muscle development.

Training variables 

Every lifter in my generation—I was born in 1973—started out with the idea that three sets of 10 is ideal for hypertrophy … and for everything else, come to think of it. It’s not wrong so much as limited.

Here’s what we’ve learned about sets, reps, and all the other variables you consider for your clients’ programs.

Reps

We now know there’s no ideal rep range for hypertrophy. Unless you go extremely low (fewer than five per set) or extremely high (50 or more), you can build muscle.

That leaves us with a range of six to 49 reps. But we can narrow it down quite a bit.

At the high end, can you imagine having your clients do more than 30 per set? Unless they really enjoy pain and discomfort, I don’t think they’d be your clients for long.

At the low end, few general-population clients need to train with heavy loads requiring fewer than eight reps. I never do in my own workouts; after training for 20-plus years, the injury risk just isn’t worth it to me.

So what’s ideal?

For most movements, probably eight to 12 per set, and maybe 12 to 20 for some isolation movements. Surprisingly, there’s no need to vary your reps from workout to workout, or even month to month. You may want to, with the goal of keeping your clients engaged. But there’s no consistent evidence that it makes a difference.

READ ALSO: Sorry to Disappoint, but Muscles Don’t Get “Confused”

Sets

While the number of reps per set isn’t especially important, the number of sets is. In my own meta-analysis, published in 2010, I found that, for any given exercise, multiple sets per workout are better than a single set. Four to six sets also came out better than two to three sets.

That shouldn’t be a surprise unless you’re a zealot for super-slow or HIIT.

But that’s only a small part of the puzzle. What matters most for hypertrophy is the total number of sets per muscle group per week. In a 2017 study, my coauthors and I found that for each additional weekly set, muscle size increases by 0.38 percent.

We didn’t have enough data to find an upper limit, where additional sets might produce diminishing returns, or even have negative consequences. All we can say with confidence is that you’re most likely to get the best results with 12 to 18 sets per week.

In bodybuilding terms, that would be double-digit sets for chest, shoulders, back, biceps, triceps, quads, hamstrings, glutes, and calves. And who knows what you’d do for your core, assuming you had any time left.

That approach is obviously impractical for your clients. Fortunately, you can use compound movements to hit the target.

Let’s say, in an average week, you do 12 total sets of pushing exercises—three sets of flat bench presses on Monday; three sets of shoulder presses and three sets of push-ups on Wednesday; and three sets of incline bench presses on Friday. Like a creative accountant, you can say that counts as:

• 9 sets for chest
• 12 sets for shoulders (although mostly the front deltoids)
• 12 sets for triceps

And let’s say you typically do nine sets of pulling exercises per week—three sets of dumbbell rows on Monday, three sets of pulldowns on Wednesday, and three sets of TRX inverted rows on Friday.

If you count each of those sets for both back and biceps, you’re already close. Add one additional set per workout, and you have 12 per week.

The same idea applies to lower-body exercises. A squat, for example, can count toward the volume total for quads and glutes.

Exercise selection

One question you may have: If a compound exercise counts toward your set volume for multiple muscle groups, do your clients need to do any single-joint exercises?

The short answer is no. It’s completely counterintuitive, but studies with both beginners and experienced trainees show no advantage to adding single-joint exercises like curls and extensions on top of the big-bang movements like presses and pulls.

It really comes down to how much time you have, and what your clients prefer. If you’re training a guy who’s interested in muscle development, you’d expect him to be disappointed if he doesn’t get to do his bro curls. Same with a female client who wants to focus on her glutes. Exclude those exercises at your peril.

I should also add that these studies are based on average responses. It’s entirely possible that some clients will respond better to a mix of compound and isolation exercises than to a steady diet of multijoint movements.

But there’s one key aspect of these studies that applies to everyone.

Intensity

All the aforementioned data is based on sets to failure, or near failure.

Warm-up sets don’t count. Nor does the total include the kind of sets most trainees do on their own, where they stop at a predetermined rep count whether the muscles are fatigued or not.

You should also consider that some exercises may accomplish more with less volume. For example, an exercise that loads a muscle under stretch, like an overhead triceps extension, creates more muscle damage than a pressdown or kickback. Some research suggests training a muscle through a full range of motion like this may offer a more potent hypertrophy stimulus.

Rest

Most of us learned a simple guideline for rest periods:

• Short rest for light weights and high reps
• Long rest for heavy weights and low reps

But in bodybuilding culture, there was a different idea: With short rest periods, you get a better pump, as well as a greater stimulus for testosterone and growth hormone. Most of us know how that math works:

Pump + anabolic hormones = gainz!

We now know that the brief post-workout increase in muscle-building hormones is unrelated to muscle growth.

READ ALSO: Stop Training Your Clients Like CrossFitters, Bodybuilders, or Powerlifters

In fact, the best data we have shows that longer rest periods—at least two minutes between sets with moderately heavy loads—produce better results. The reason comes down to the fact you do more work when your muscles have more time to recover between sets.

Obviously, your clients aren’t paying you to watch them stand around for two minutes after every set. But the solution is something you probably do already: Alternate two or more exercises for unrelated muscle groups, so each one has enough time to recover.

Protein volume and timing

This is one area where the gym bros have been right along: Higher protein really is beneficial for hypertrophy. The magic number to maximize gains appears to be 1.6 grams per kilogram of body weight per day, or 0.75 grams per pound. The upper limit is probably 2.2 grams per kilogram, or 1 gram per pound.

By “upper limit,” I don’t mean that your kidneys explode if you have more. That’s just the highest amount linked to muscle growth in high-quality research. Eating more isn’t dangerous; we just don’t have good reason to believe it offers any additional benefit.

Are supplements required to maximize gains? I wouldn’t say you need them, but in a recently published study, my coauthors and I found clear benefits. Protein supplements significantly increased both muscle strength and size.

Two other interesting results:

• Supplements are more effective in trained vs. untrained lifters.
• The effects diminish with age.

That’s good news for your beginner-level clients. Because their bodies are primed to respond to your training program, you can advise them to save their money and focus instead on protein-rich whole foods.

For your older clients, the news isn’t necessarily bad. The studies showing less muscle growth used lower protein doses than you typically see in these studies—20 grams per day instead of 40. The take-away message is that older lifters probably need something close to 40 grams to maximize protein synthesis post-workout.

Timing

Right now, there’s not much evidence that timing has a significant impact on muscle gains. As long as you have some protein roughly two to three hours before training and two to three hours after, timing isn’t likely to make much of a difference.

What matters most is your total protein intake. I don’t want to say that timing doesn’t matter at all, but it seems to be much, much less important than your daily total.

The final tally

If you’re keeping score, it should now be clear that traditional gym culture has gotten a lot of things right over the years:

• Moderate rep ranges—eight to 12 per set, and up to 20 for some movements—are typically best for hypertrophy.
• Each additional set can be linked to bigger muscles. There must be an upper limit, but we don’t know exactly what it is.
• Training to or near failure on most of those sets will produce the best results.
• More protein means more muscle, up to 1.6 to 2.2 grams per kilogram of body weight, or 0.75 to 1 gram per pound.

But bro science, collectively, has also been wrong on a couple of points:

• Short rest periods may give you a great pump, but if you recover two minutes or more between sets, you’ll do more reps, and get better results.
• Adding isolation exercises may not offer much benefit over compound movements, especially in untrained lifters. What matters is the total number of sets for each muscle group.
• Pre- and post-workout protein doesn’t have to be as precisely timed as meatheads tend to believe. Total daily intake matters much more.

How you apply all this to your clients depends entirely on where they are and where they want to go. Just keep in mind you don’t have to apply all of it at once. Each step in the right direction will eventually pay off with bigger, better-looking muscles. And like I said, nobody ever complains about those.