“Effective Reps”: 5 Reps Is All It Takes for Maximum Hypertrophy?

The "effective reps model" argues that only (only!) the last 5 reps you do to failure stimulate muscle growth. Is it right? Or pure rubbish?

Athletic muscular scientists with sleeveless lab coats looking puzzled, thinking about effective Reps range
“I don’t count my sit-ups; I only start counting when it hurts because they’re the only ones that count.” — Muhammad Ali, “the Greatest” American professional boxer and activist.

Um, cool. But what’s that got to do with muscle-building? 🤔

Well, according to the proponents of the "effective reps model”, everything.

From a logical standpoint, you probably know that not all reps are created equal. For example, if you're used to BB back squatting 100 kg, 3 reps of 50 kg would be less growth-stimulating than 3 reps of 100 kg.

That’s reasonable … but where should we draw the line? Case in point: how does 7 reps of 90 kg stack up against 3 reps of 100 kg?

The “effective reps model” attempts to accurately predict the amount of muscle growth you’d see from any reps x load by specifying the exact number of hypertrophy-stimulating reps.

What are “effective reps”?


OK, maybe this will make things clearer. The “effective reps model” basically argues that only the last 5 reps before failure stimulate hypertrophy because, supposedly:

  1. Full motor unit recruitment occurs around 5 reps from failure (some background info: we recruit motor units from the smallest to largest, and EMG research shows that muscle electrical activity increases early in a set, then plateaus approximately 5 reps before failure)
  2. When a muscle is close to failure, the speed at which it changes length during a contraction (i.e., contraction velocity) slows — increasing the amount of mechanical tension each recruited fiber undergoes. Since mechanical tension is the primary driver of hypertrophy, meaning ~5 reps to failure are when the working muscle is subject to the most growth stimulus.
So, given those, the proponents of the “effective reps model” argue there’s no point in doing 15 reps with a 15RM load since you’d achieve the same growth with just 5 reps with a 5RM load.

You’d be clocking in those 5 “effective reps” either way.

How do reps actually work? (Like, based on credible science)

At first glance, the "effective reps model" idea is pretty compelling.

After all, research shows similar muscle growth across a wide array of rep ranges, provided the sets are taken close to failure.

Learn more here:

How Many Sets and Reps Should You Do to Build Muscle?
The higher your training volume, the more gains you’ll get ... right? Wrong. Find out exactly how many sets and reps you should do right here.

But look closer, and you’ll start noticing cracks in the model, such as:

  • Training in the <5 reps range should lead to poorer muscle growth: If there are 5 “effective reps”, clocking anything less should lead to less hypertrophy. Alas, several studies strongly suggest otherwise.
2015 study published in Physiological Reports: The researchers compared the effects of training at 3-5 RM loads (i.e., 3-5 reps to failure) versus 10-12 RM loads (i.e., 10-12 reps to failure) and found that participants reported significantly greater gains in arm lean mass in the former condition.
2000 study published in the Journal of Orthopedic and Sports Physical Therapy: The researchers compared the effects of training at 3-5 RM loads versus 11-13 RM loads and found no significant differences in hypertrophy of the participants’ quads or hamstrings.
  • Really light load should produce comparable results when brought to failure: By "really light load", we mean ~20% of 1RM (~60 reps to failure). According to a 2018 study published in the European Journal of Sport Science, the participants who’d trained at 20% of their 1RM experienced half the biceps and quads growth than those who did 40% (~40 reps to failure), 60% (~20 reps to failure), and 80% (~8 reps to failure) of their 1RM.
  • You may not need to get to ~5 reps to failure for full motor recruitment: Perhaps the most damning of all … multiple EMG analyses have found that the electrical activity (or activation) of the primary target muscles barely changed even as the load for various compound movements — including the BB back squat and flat bench press — increased from ~50% to 90%. This suggests that trained lifters may be able to recruit almost all primary motor units trained by a multi-joint exercise even with substantially lower loads and when far away from failure.

So, if we cannot trust the "effective reps model, " how do reps "work" to stimulate hypertrophy? Is there another way to accurately predict how much muscle growth we'd see from any given set x load done during strength training?

Unfortunately, that’s something sports science researchers are still figuring out.

What does this mean for you?

In the meantime, though, what'd make more sense for you is to think of every single rep you do as hypertrophy-stimulating — and give it your all.

Don't fixate on, "Oh, let's pick a heavy-ass weight that I can only do 5 reps with since they're the only effective ones."

Obviously, that isn’t to say you can’t train heavy.

Instead, it’s just to say that you have the flexibility to:

  • Pick a rep range you can sustainably and enjoyably train with: Note that your chosen rep range can vary from exercise to exercise. For example, you could do 6-8 reps for the BB deadlift and 12-15 on the glute kickbacks. It's up to you. Just monitor your recovery and adjust your training volume/intensity as needed.
  • Make sure to go close to failure: While we cannot quantify the exact number of “effective reps”, what research has consistently now made very clear is that you must go close enough to failure for optimal muscle growth. Meaning? If your training session feels like a piece of cake, you’re taking things wayyyy too easy.

Exercise selection, sets and reps, progressive overload — all built into your training plan

Flexibility is great … if you have the bandwidth or desire to plan your own workouts.

And TBH, actually planning those sessions can be a real headache. Before picking a suitable rep range, you'd need to consider exercise selection, load, and number of sets. Then, once all that's done, there's also periodic progressive overload to think of.

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Król, Henryk, and Artur Gołaś. “Effect of Barbell Weight on the Structure of the Flat Bench Press.” Journal of Strength and Conditioning Research, vol. 31, no. 5, May 2017, pp. 1321–37. PubMed Central, https://doi.org/10.1519/JSC.0000000000001816.

Lasevicius, Thiago, et al. “Effects of Different Intensities of Resistance Training with Equated Volume Load on Muscle Strength and Hypertrophy.” European Journal of Sport Science, vol. 18, no. 6, July 2018, pp. 772–80. PubMed, https://doi.org/10.1080/17461391.2018.1450898.

Mangine, Gerald T., et al. “The Effect of Training Volume and Intensity on Improvements in Muscular Strength and Size in Resistance-Trained Men.” Physiological Reports, vol. 3, no. 8, Aug. 2015, p. e12472. PubMed Central, https://doi.org/10.14814/phy2.12472.

McBride, Jeffrey M., et al. “Effect of Absolute and Relative Loading on Muscle Activity during Stable and Unstable Squatting.” International Journal of Sports Physiology and Performance, vol. 5, no. 2, June 2010, pp. 177–83. PubMed, https://doi.org/10.1123/ijspp.5.2.177.

“One Rep Max Calculator.” Strength Level, https://strengthlevel.com/one-rep-max-calculator. Accessed 28 July 2023.

Schoenfeld, Brad J., et al. “Strength and Hypertrophy Adaptations Between Low- vs. High-Load Resistance Training: A Systematic Review and Meta-Analysis.” Journal of Strength and Conditioning Research, vol. 31, no. 12, Dec. 2017, pp. 3508–23. PubMed, https://doi.org/10.1519/JSC.0000000000002200.

---. “Strength and Hypertrophy Adaptations Between Low- vs. High-Load Resistance Training: A Systematic Review and Meta-Analysis.” Journal of Strength and Conditioning Research, vol. 31, no. 12, Dec. 2017, pp. 3508–23. PubMed, https://doi.org/10.1519/JSC.0000000000002200.

Sugi, Haruo, and Tetsuo Ohno. “Physiological Significance of the Force-Velocity Relation in Skeletal Muscle and Muscle Fibers.” International Journal of Molecular Sciences, vol. 20, no. 12, 12, Jan. 2019, p. 3075. www.mdpi.com, https://doi.org/10.3390/ijms20123075.

Sundstrup, Emil, et al. “Muscle Activation Strategies during Strength Training with Heavy Loading vs. Repetitions to Failure.” Journal of Strength and Conditioning Research, vol. 26, no. 7, July 2012, pp. 1897–903. PubMed, https://doi.org/10.1519/JSC.0b013e318239c38e.

van den Tillaar, Roland, et al. “Comparison of Muscle Activation and Kinematics during Free-Weight Back Squats with Different Loads.” PloS One, vol. 14, no. 5, 2019, p. e0217044. PubMed, https://doi.org/10.1371/journal.pone.0217044.

Weiss, L. W., et al. “Gross Measures of Exercise-Induced Muscular Hypertrophy.” The Journal of Orthopaedic and Sports Physical Therapy, vol. 30, no. 3, Mar. 2000, pp. 143–48. PubMed, https://doi.org/10.2519/jospt.2000.30.3.143.