The Best Reps for Building Muscle Mass Revealed -

A 2025 study by Cumming et al., explored whether low-load or high-load training is better for building muscle in trained individuals. Fourteen experienced lifters trained one leg with heavy weights (3–5 reps) and the other leg with lighter weights (20–25 reps)—both to failure—for nine weeks.mThe key takeaway? Both rep ranges led to similar increases in muscle thickness, proving that training intensity (pushing sets to failure) matters more than the weight itself. Interestingly, only the heavy-load leg saw significant strength gains in isolated exercises like leg extensions. However, when it came to muscle size, the body responded equally to high or low reps—as long as the effort was maximal. Muscle fiber size didn’t increase significantly in either group, but satellite cell activity did—suggesting early-stage adaptations that may support longer-term hypertrophy. These findings reinforce that the best reps for building muscle mass are not about a magic number, but about how hard you push. So whether you're lifting heavy or going high-rep, you can still build serious muscle—as long as you train with intent.

Why Training to Failure May Be the Real Key Behind the Best Reps for Building Muscle Mass:

Low-load (20–25 reps) and high-load (3–5 reps) resistance training produced similar increases in muscle thickness. When considering the best reps for building muscle mass, it’s important to find the right balance that works for your body.
High-load training led to better strength gains in isolated movements like leg extensions.
Taking sets to volitional failure matters more than the number of reps when it comes to hypertrophy.

Introduction: Rethinking the Best Reps for Building Muscle Mass

For decades, lifters have followed the classic advice: if you want to get bigger, lift in the 6–10 rep range. This range was thought to offer the best reps for building muscle mass, balancing mechanical tension and fatigue to hit that hypertrophy “sweet spot.”

But what if that’s only part of the story?

A new study by Cumming et al. (2025), published in the Journal of Applied Physiology, challenges that assumption. The researchers looked at trained lifters—people like you—over a 9-week training program to compare low reps (3–5) vs high reps (20–25) when sets were taken to failure.

The results? Muscle growth happened in both cases. Which means the best reps for building muscle mass might not be about numbers at all—but about effort.

Review of the Literature: What Does the Science Say About Rep Ranges?

The belief in the 6–10 rep range has strong roots. It sits between strength-focused training (1–5 reps) and endurance-focused rep ranges (15+ reps), giving it the reputation of being the best rep range for hypertrophy.

But evidence from the last two decades paints a more complex picture.

Key Findings:

Campos et al. (2002): Gains in muscle size can occur at both low and high reps, depending on volume.
Morton et al. (2020): Similar hypertrophy occurred across various rep ranges when training was taken to failure.
Nuzzo et al. (2023): Volume and effort drive hypertrophy more than the exact number of reps.

So while the 6–10 rep range is effective, it may not be the only—or even the best reps for building muscle mass—especially if you’re consistently training to failure.

Study Summary: What Did Cumming et al. (2025) Discover?

The 2025 study by Cumming and colleagues is one of the most relevant pieces of research for trained individuals trying to optimize their rep range for muscle hypertrophy.

Study Design Focused on Trained Lifters Seeking the Best Reps for Muscle Growth

Participants: 14 trained men and women, age 26 on average.
Design: Each person trained one leg with high-load (3–5 reps) and the other with low-load (20–25 reps) for 9 weeks.
Protocol: All sets taken to volitional failure.

Key Results That Reveal the Most Effective Rep Ranges for Hypertrophy:

Muscle growth (via ultrasound): Similar in both groups (~7–8% increase in thickness).
Strength: Better in the high-load leg for single-joint movements.
Fiber size: No significant change in cross-sectional area.
Satellite cell activity: Increased in both groups, especially in Type I fibers.

This means hypertrophy isn’t limited to moderate loads. It supports the idea that best reps for building muscle mass can vary—and depend more on intensity than numbers.

Why Training to Failure May Be the Real Key Behind the Best Reps for Building Muscle Mass

So what’s the real takeaway here?

It’s not that the 6–10 range is wrong. It still works—really well in fact. But it’s no longer the only option. Cumming et al. showed that both 3–5 reps and 20–25 reps, when pushed to failure, can stimulate similar muscle growth.

So what’s happening?

Low reps = more mechanical tension, which improves strength.
High reps = more metabolic stress, which promotes hypertrophy.
Both pathways can lead to muscle growth—if the muscle is pushed hard enough.

Bottom line: the best reps for building muscle mass aren’t just about picking the right number. It’s about intensity, effort, and progression.

Application: How to Find Your Best Rep Range for Muscle Growth

Whether you’re a seasoned gym-goer or just fine-tuning your program, here’s how to apply this research in the real world:

1. Train to (or near) Failure

The study shows that the stimulus matters more than the rep count. Push every working set hard.

2. Vary Your Reps Strategically

Use 3–6 reps for strength and compound lifts.
Use 6–12 reps for bread-and-butter hypertrophy.
Use 15–25 reps for light days, isolation work, or joint-friendly sessions.

3. Periodize Your Training

Alternate training blocks focusing on different rep ranges to keep gains coming and avoid plateaus.

4. Monitor Progress, Not Just Weight

Track your reps, load, and how close you are to failure. That’s what drives growth.

FAQ: People Also Ask About Best Reps for Building Muscle Mass

What are the best reps for building muscle mass?

The 6–10 rep range is traditionally used for hypertrophy, but research shows that both low reps (3–5) and high reps (15–25) can also be effective when taken to failure.

Is 5 reps too low for muscle growth?

Not at all. Heavy training in the 3–5 rep range promotes strength, which can support hypertrophy over time. When pushed hard, even low-rep sets contribute to muscle gains.

Do higher reps build muscle or endurance?

Both! High reps build muscular endurance, but when performed to failure, they also stimulate muscle growth. The key is effort, not just rep count.

Should I always train to failure?

Not necessarily every set, but research shows that taking sets close to failure maximizes fiber recruitment—especially with lighter weights.

What’s better for hypertrophy: 3 sets of 10 or 5 sets of 5?

Both can work. What matters most is total volume and intensity. If you’re lifting heavy with 5 sets of 5 and hitting failure, you’re still stimulating growth.

Conclusion: Are 6–10 Reps Still the Best Reps for Building Muscle Mass?

Yes—and no.

The 6–10 rep range is still a fantastic tool for hypertrophy. It balances weight, volume, and fatigue. But it’s not the only way. This new study confirms that both light and heavy loads can build muscle—as long as you go hard.

So if you’re tired of joint pain, want variety, or just need a new challenge, it’s totally legit to break out of the old mold.

Because when it comes to the best reps for building muscle mass, the real answer is this: It’s not about how many reps you do. It’s about how hard you’re willing to push them.

References

Campos, G. E. R., Luecke, T. J., Wendeln, H. K., Toma, K., Hagerman, F. C., Murray, T. F., … & Staron, R. S. (2002). Muscular adaptations in response to three different resistance-training regimens: specificity of repetition maximum training zones. European Journal of Applied Physiology, 88(1-2), 50–60. https://doi.org/10.1007/s00421-002-0681-6
Cumming, K. T., Elvatun, I. C., Kalenius, R., Divljak, G., Raastad, T., Psilander, N., & Horwath, O. (2025). Divergent strength gains but similar hypertrophy after low-load and high-load resistance exercise training in trained individuals: Many roads lead to Rome. Journal of Applied Physiology, 139(3), 685–697. https://doi.org/10.1152/japplphysiol.00353.2025
Morton, R. W., Oikawa, S. Y., Wavell, C. G., Mazara, N., McGlory, C., Quadrilatero, J., … & Phillips, S. M. (2016). Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men. Journal of Applied Physiology, 121(1), 129–138. https://doi.org/10.1152/japplphysiol.00154.2016
Moro, T., Monaco, L., Naro, F., Reggiani, C., & Paoli, A. (2022). Exercise intensity and rest intervals effects on intracellular signals and anabolic response of skeletal muscle to resistance training. The Journal of Strength and Conditioning Research, 38(10), 1695–1703. https://doi.org/10.1519/jsc.0000000000004209
Nuzzo, J. L., Pinto, M. D., Nosaka, K., & Steele, J. (2023). Maximal number of repetitions at percentages of the one repetition maximum: a meta-regression and moderator analysis of sex, age, training status, and exercise. Sports Medicine, 54(2), 303–321. https://doi.org/10.1007/s40279-023-01937-7