200 Lifters Trained 6 Days vs 3 Days a Week for 10 Weeks. The Muscle Growth Results Were Almost Identical

Jeremy Ethier just wrapped up one of the largest independent muscle growth experiments ever conducted outside a university lab, and the results challenge everything most lifters believe about training volume.

Over 200 people spent 10 weeks following either a six-day-per-week program or a three-day-per-week routine with half the total sets.

What happened next shocked even the researchers involved.

Both groups grew almost exactly the same amount of muscle, despite one group doing twice as much work.

The Experiment That Changed Everything

Ethier recruited 200 real lifters and randomly assigned them to one of two training groups. The first group followed a six-day push-pull-legs split with roughly 20 sets per muscle per week. The second group did the same split but trained only three days per week with half the sets.

Both groups followed a controlled nutrition plan tracked through the Built With Science app, with a small calorie surplus and minimum daily protein targets. Anyone who didn’t stay consistent was removed from the study.

Each group was balanced for gender and experience level, containing equal numbers of beginner and intermediate lifters. Participants submitted weekly circumference measurements of flexed and unflexed muscles to track progress.

With this kind of design, what we do is we sacrifice the high-tech body comp measurements so that we can expand out and get a more, you know, a larger, more representative sample.

Dr. Eric Trexler, a statistician and muscle growth researcher, helped design the experiment and independently analyzed all the data after the 10-week period concluded.

The Six-Day Group Started Struggling Early

Just three weeks into the program, clear differences emerged between the groups. The six-day-per-week participants consistently reported their workouts feeling harder and never getting easier.

This week I missed a few morning workouts. Had to do them at night after leaving the office. I started to dislike the 6-day split a bit.

Meanwhile, the three-day group rated their sessions as feeling easier week after week. They also reported higher energy levels and greater enthusiasm for training.

Going into the gym only 3 days a week, I am giving 110% rather than cutting corners here and there.

One participant from the three-day group described waking up wanting to work out instead of dreading it, a stark contrast to how six-day participants felt.

Why the Six-Day Group Should Have Won

Over a decade of research supports the dose-response relationship between training volume and muscle growth. Most studies suggest that doubling your weekly sets should produce roughly 60% more gains.

Based on this research, the six-day group should have seen combined growth of about 1.2 inches instead of just 0.83 inches. The three-day group was expected to lag behind significantly.

But there was a critical flaw in applying lab research to real-world training.

The Shocking Results

After 10 weeks, Dr. Trexler crunched the numbers. Combined growth in the six-day program averaged 0.83 inches, while the three-day program produced 0.75 inches of growth.

Now, you might say, you know, that looks like a meaningful difference, but it’s important to understand that that was not nearly a significant difference between the two and any statistician would look at these data and say those two groups essentially grew the same amount.

Despite doing half the training, the three-day group grew statistically the same amount as the six-day group.

Why More Sets Didn’t Equal More Growth

Dr. Eric Helms, a muscle researcher and natural pro bodybuilder, explained that muscles only respond to actual muscle-building stimulus, not just the number of sets written in a program.

In my experience, most people who push to higher frequencies and higher volumes, they end up sacrificing other aspects of their program.

When training volume increases dramatically, lifters often subconsciously hold back on effort or let form slip as fatigue accumulates. The total workload may look higher on paper, but the actual stimulus delivered to muscles remains similar.

The Pacing Problem

A 2014 study revealed an interesting psychological phenomenon. Researchers had people perform 12 sets of maximal isometric bicep contractions, instructing everyone to produce maximum force on every set.

Half the participants knew they’d be doing 12 total sets. The other half were told they’d only do six sets (though they actually did 12).

The group expecting 12 sets paced themselves and consistently produced less power than the group thinking they only had six sets ahead. Even when told to go all-out, knowing more work was coming caused people to hold back.

This likely explains what happened in Ethier’s six-day group. Just knowing they had twice as much training to get through may have caused subconscious pacing, reducing the quality of each individual set.

Why Lab Studies Still Show Volume Works

Research studies are designed to isolate one variable while controlling everything else. When volume increases in a lab setting, participants receive direct supervision to ensure they maintain effort and form consistency.

Most people do not train hard enough in their training. When we get them in to the lab and we push the crap out of them.

A brand new study published just before Ethier’s video compared supervised training against the exact same program done without supervision. After eight weeks, the supervised group gained more than a pound of additional fat-free mass and grew more in nearly every muscle measured.

In real-world training, unless someone watches every rep, you’re left managing intensity yourself. If you don’t, much of your extra gym time could be wasted effort.

Three Tests to Know If You’re Wasting Time

Ethier recommends three simple tests to determine whether your training is actually productive or just going through the motions.

Test One: Rep Speed

If you’re pushing hard enough, your last few reps should move noticeably slower than your first reps. If all reps move at similar speeds, you’re likely stopping too soon and leaving gains on the table.

Test Two: Rep Drop-Off

When doing multiple sets with the same weight, you should see some performance decline. If 12 reps in set one becomes 11 in set two and 9-10 in set three, you’re pushing appropriately hard.

If reps stay perfectly flat across sets or somehow increase on your final set, you didn’t push hard enough in earlier sets.

Test Three: Progressive Overload

Look back at the last two to three months of training. Are you consistently adding reps or weight on your main lifts?

If yes, your program is working. If you’re training five or six days weekly and lifts haven’t moved in months, you might benefit from cutting back volume.

Well, it might not be a terrible idea to do a little experiment with yourself. You know, try to cut down on your volume for a training block or two, really push your intensity, be very intentional about bringing effort into your sessions.

The Highest-Performing Program Surprised Everyone

Ethier actually tested a third group that posted the best results of the entire experiment. This group took all the volume from the six-day split and packed it into three full-body workouts using supersets to save time.

The difference is very small and not statistically significant, but technically, the program that caused the most growth was the 3-day full-body program. It led on average to a growth of 0.87 inches.

Training each muscle group more frequently while keeping total volume the same prevented the performance drop-off that happens when doing set after set of the same exercise.

What Advanced Lifters Should Do

For lifters who genuinely know how to train hard with perfect form regardless of total volume, higher training volumes can still produce marginal benefits.

Shortly after Ethier’s experiment concluded, researchers published a similar study with over 100 trained lifters. They compared roughly 36 weekly sets for arms and thighs against just nine sets—four times the volume difference.

Every workout was supervised to ensure high-volume participants maintained effort on all sets. If high volume was ever going to dominate, this should have been it.

The data do slightly favor the higher volumes in this study, but the difference is probably what most people would consider non-meaningful. I think that’s just worth acknowledging that every single set you start adding, and especially as you get into the teens and 20s, is such a marginal return on investment.

Dr. Eric Helms structures his own training around six full-body workouts per week, split into two separate sessions daily—one morning, one evening. This maximizes total volume while keeping each session’s quality as high as possible.

Practical Recommendations Based on Your Goals

If you want to squeeze out every last bit of muscle growth and you’re confident extra volume won’t compromise effort or form, higher volumes with frequent training sessions can provide small additional benefits.

For advanced lifters chasing maximum growth:

• Train each muscle group at least twice per week
• Aim for 15-25 sets per muscle per week
• Consider splitting sessions (AM/PM) to maintain quality
• Use full-body or upper/lower splits for higher frequency

For lifters who want solid gains without excessive time commitment:

• Train three to four days per week
• Aim for 10-15 sets per muscle per week
• Focus on two to three high-quality sets per exercise
• Full-body or upper/lower splits work excellently

If you’re currently training five to six days weekly without seeing consistent progress, cutting back volume while increasing intensity on each set may actually accelerate results.

The Bottom Line

More training isn’t always better training. Quality matters far more than quantity, especially when fatigue and time constraints cause effort to drop.

For most lifters, three to four well-executed workouts per week with 10-15 sets per muscle will deliver 90-95% of maximum possible gains. Adding significantly more volume provides diminishing returns unless you’re an elite athlete willing to make training your life.

The real secret isn’t finding the perfect number of sets. It’s consistently pushing those sets hard enough to create a genuine growth stimulus, week after week, month after month.

Choose a training frequency you can sustain long-term with high effort on every set, support it with adequate nutrition and recovery, and let consistency do the heavy lifting.