Should You Leave Reps in Reserve?
Training to failure has long been one of bodybuilding’s most debated muscle-building techniques. For decades, bodybuilders like Dorian Yates and Mike Mentzer have pushed sets until they physically cannot complete another repetition. The logic seems straightforward: if you want a muscle to grow, you need to push it as hard as possible.
But does training to failure actually build more muscle, or are you simply creating additional fatigue, unnecessary breakdown, and risking injury?
Current research suggests the answer falls somewhere in the middle.
Training close to failure appears to be an important consideration for maximizing muscle growth, particularly when using lighter loads. However, consistently taking every set to absolute muscular failure doesn’t appear necessary for hypertrophy and may create additional fatigue that interferes with the rest of your workout.
Our team at Generation Iron is taking a look at what the science says about training to failure, muscle growth, strength, and how close to failure you should actually train.
What Is Training to Failure?
Training to failure means continuing a set until you cannot perform another complete repetition with proper technique.
Imagine performing curls with a set of dumbbells.
You complete 10 reps. Then 11. Then 12.
You attempt rep 13, but despite maximal effort, you cannot complete the repetition through the intended range of motion.
You’ve reached momentary muscular failure.
However, defining failure isn’t always as straightforward as it sounds. Research has used several different definitions, including momentary muscular failure, set failure, and different thresholds of velocity loss. This inconsistency is one reason comparing failure-training studies can be difficult.
For practical bodybuilding purposes, it helps to distinguish between technical failure and momentary muscular failure.
Technical failure occurs when you can no longer perform another repetition with acceptable technique.
Momentary muscular failure occurs when you physically cannot complete another repetition despite attempting to do so.
Those aren’t necessarily the same point.
Does Training to Failure Build Muscle?
Yes, training to failure can build muscle. The more important question is whether it builds more muscle than stopping slightly before failure.
That’s where the evidence becomes more interesting.
A systematic review and meta-analysis comparing failure and non-failure resistance training found no significant overall difference in muscle hypertrophy between the two approaches. The researchers concluded that training to muscular failure does not appear to be required for increasing muscle size.
A separate meta-analysis examining proximity to failure similarly found no evidence that reaching momentary muscular failure produces greater hypertrophy than stopping before failure.
However, that doesn’t mean effort doesn’t matter.
More recent research examining proximity to failure as a continuum found that muscle hypertrophy tended to improve as sets were terminated closer to failure. The researchers cautioned that the precise relationship remains uncertain, but the findings support the idea that proximity to failure matters for muscle growth.
In other words: You probably don’t have to reach absolute failure, but you shouldn’t make every working set easy either.
What Are Reps in Reserve?
One of the easiest ways to manage training intensity is through repetitions in reserve, commonly abbreviated as RIR.
RIR estimates how many additional repetitions you could have completed before reaching failure.
For example:
- 4 RIR: You could have performed approximately four more reps.
- 3 RIR: You had approximately three reps remaining.
- 2 RIR: You could probably have completed two more reps.
- 1 RIR: You had approximately one good repetition remaining.
- 0 RIR: You’ve reached failure.
Instead of requiring every set to end at failure, bodybuilders can use RIR to regulate effort.
A challenging set might finish with approximately one or two repetitions left in the tank.
This allows you to train extremely hard without necessarily grinding through an unsuccessful repetition every time you touch a weight.
How Close to Failure Should You Train for Muscle Growth?
There isn’t one magical RIR target that guarantees maximum hypertrophy.
However, the emerging evidence suggests that muscle growth tends to improve as sets are performed closer to failure, while the exact point at which additional effort stops producing meaningful benefits remains uncertain.
For practical bodybuilding training, many working sets can therefore be performed close to failure without necessarily reaching absolute failure.
This distinction becomes particularly useful during exercises such as:
Taking a heavy compound exercise to complete failure can create considerable fatigue and may also leave you in a compromised position if appropriate safety equipment or spotting isn’t available.
Stopping shortly before failure can still produce an extremely demanding set while allowing you to better manage fatigue and maintain technique.
Why Training Close to Failure Builds Muscle
Resistance training provides mechanical tension to muscle fibers. As a challenging set progresses, fatigue accumulates and maintaining force production becomes increasingly difficult.
This is part of the reason the final repetitions of a hard set feel dramatically different from the first few.
The closer you move toward failure, the more demanding the set becomes.
This doesn’t mean the final rep before failure possesses some magical muscle-building property. Instead, proximity to failure is one way of ensuring that a set provides a sufficiently challenging stimulus.
The key distinction is between training hard and training to absolute failure.
They aren’t necessarily the same thing.
Does Training to Failure Build More Muscle Than Stopping Short?
Not necessarily.
A 2022 systematic review and meta-analysis found no significant overall difference in hypertrophy between resistance training performed to failure and non-failure training. Interestingly, a subgroup analysis did find a small advantage for failure training among resistance-trained participants, but the authors still concluded that failure was not required for gains in muscle size.
Another meta-analysis found that failure training produced greater hypertrophy in its overall analysis, but that advantage disappeared when training volume was equated between failure and non-failure groups.
Taken together, the evidence suggests that training effort and proximity to failure matter, but actually hitting failure on every set probably isn’t necessary to maximize muscle growth.
The Downside of Training to Failure
If failure training can stimulate muscle growth, why not simply take every set to failure?
Fatigue. Training to failure is demanding.
A review examining proximity to failure found that failure training may increase neuromuscular fatigue, muscle damage, and perceived discomfort compared with stopping before failure. Those effects could potentially influence subsequent training performance and recovery.
Imagine you have four sets of bench presses. If you completely exhaust yourself on the first set, your performance during sets two, three, and four may suffer.
You might perform fewer repetitions, use less weight, or struggle to maintain technique.
That’s where managing fatigue becomes important.
The goal of a bodybuilding workout isn’t necessarily to destroy yourself during one set.
It’s to accumulate enough high-quality training stimulus across the entire workout and training week to promote adaptation.
Training to Failure vs. Training Close to Failure
Consider two lifters performing the same exercise.
Lifter A
Performs every set to complete muscular failure.
Lifter B
Performs most sets with approximately one or two reps in reserve and occasionally takes the final set to failure.
Both lifters are training hard.
But Lifter B may be able to maintain better performance across the entire session while still performing sets sufficiently close to failure to stimulate muscle growth.
That’s why failure training is better viewed as a tool rather than a requirement.
Is Training to Failure Better for Strength?
The argument for failure training becomes even weaker when the primary goal is maximal strength.
A meta-analysis examining failure versus non-failure training found no significant overall advantage for failure training in developing maximal strength. When training volume wasn’t equalized, non-failure training actually produced greater strength improvements.
Another systematic review similarly found a small overall effect favoring non-failure training for strength development.
Strength training involves more than simply exhausting a muscle.
Technique, force production, movement quality, neurological adaptations, and repeated exposure to heavy loads are all important.
Constantly grinding repetitions to failure isn’t necessarily the best way to improve those qualities.
Should Beginners Train to Failure?
Beginners generally don’t need to take every set to failure. Someone new to resistance training can make significant progress without pushing every exercise to their absolute limit.
There’s another issue: beginners may not yet know what true muscular failure feels like.
Learning proper technique, developing consistency, and progressively increasing training demands should take priority.
As experience increases, lifters generally become better at estimating how many repetitions they have remaining.
That makes techniques such as RIR increasingly useful.
Should Advanced Bodybuilders Train to Failure?
Failure training may become more useful for experienced bodybuilders. Advanced lifters typically require a greater training stimulus to continue progressing than beginners, and they are often better at accurately judging proximity to failure.
That still doesn’t mean every set needs to reach failure. Instead, advanced lifters can strategically incorporate failure training when appropriate.
For example, failure might make more sense during the final set of:
- Cable curls
- Triceps pushdowns
- Lateral raises
- Leg extensions
- Leg curls
- Machine chest presses
- Cable flyes
These exercises are generally easier to terminate safely when another repetition becomes impossible.
Should You Take Compound Exercises to Failure?
More caution should be used when taking heavy compound exercises to complete failure.
Exercises such as barbell squats, deadlifts, bench presses, and overhead presses require significant coordination and can become increasingly difficult to perform correctly as fatigue accumulates.
Failure on a cable curl simply means lowering the handle and ending the set.
Failure underneath a heavy barbell squat is a very different situation.
For compound movements, stopping slightly before absolute failure can often provide a strong training stimulus without unnecessarily sacrificing technique or accumulating excessive fatigue.
If you do train a barbell movement to failure, appropriate safety equipment and competent spotting are essential.
Does Training to Failure Matter More With Light Weights?
Proximity to failure may become particularly important when using lighter loads.
The 2023 systematic review on proximity to failure noted larger effect-size estimates favoring failure training when lower loads were used compared with heavier loads, providing some support for the idea that lighter-load sets may need to be taken closer to failure.
Think about performing 30 easy repetitions with a light dumbbell but stopping when you could have completed another 20.
That set probably isn’t particularly challenging.
Take that same lighter load much closer to your repetition limit, however, and the stimulus becomes considerably different.
This is particularly relevant to bodybuilding techniques involving:
- High-repetition sets
- Drop sets
- Machine exercises
- Isolation exercises
- Resistance bands
- Bodyweight exercises
The lighter the resistance, the more important it may become to ensure that the set is actually challenging.
How Often Should You Train to Failure?
There isn’t a universal number of failure sets everyone should perform each week.
Exercise selection, training experience, total volume, frequency, recovery capacity, and individual goals all matter.
A practical strategy is to keep most heavy compound sets slightly short of failure while using failure more selectively during lower-risk isolation and machine exercises.
For example:
Heavy compound movements: generally stop approximately 1–3 reps before failure.
Moderate-load bodybuilding exercises: approximately 1–2 reps from failure on many working sets.
Isolation and machine exercises: occasionally reaching failure, particularly on the final set, may be reasonable.
These are practical guidelines rather than scientifically established rules. Individual lifters should adjust them based on performance, recovery, and training experience.
Don’t Confuse Failure With Bad Form
There’s another important distinction. Reaching failure doesn’t mean doing whatever is necessary to force another repetition.
If you’re performing curls and suddenly your hips, shoulders, and lower back are doing most of the work, you’ve changed the exercise.
If your squat technique completely collapses while you attempt another repetition, continuing isn’t necessarily productive.
Muscle growth shouldn’t come at the expense of basic exercise execution.
For most bodybuilding exercises, technical failure is a sensible place to terminate a set.
Progressive Overload Still Matters
Training to failure doesn’t eliminate the need for progressive overload.
You still need to create progressive challenges over time.
That could mean:
- Increasing weight
- Performing more repetitions
- Adding productive training volume
- Improving technique
- Increasing range of motion
- Improving control
- Performing the same workload with better execution
Simply taking the same weight to failure for months doesn’t guarantee continued muscle growth.
Failure is an intensity-management technique.
It isn’t a substitute for a well-designed training program.
Recovery Matters Too
More training isn’t automatically better training. Resistance exercise creates a stimulus, but adaptation occurs during the recovery process.
If constantly training to failure causes your performance to decline, your joints to hurt, your motivation to disappear, or subsequent workouts to suffer, you’re probably not gaining anything from the additional effort.
A successful hypertrophy program needs to balance stimulus and fatigue.
That’s why stopping one repetition short of failure can sometimes be more productive than squeezing out an ugly final rep.
So, Does Training to Failure Build More Muscle?
Training to failure can absolutely be part of an effective muscle-building program. But you don’t need to take every set to failure to build muscle.
Current evidence suggests that training closer to failure is generally associated with greater hypertrophy, but research comparing actual momentary failure with non-failure training has not established that reaching absolute failure consistently produces superior muscle growth.
That distinction matters.
You need to train hard enough to challenge your muscles.
You don’t necessarily need to completely exhaust them every time.
The Bottom Line
Training to failure can build muscle, but failure itself isn’t a requirement for muscle growth.
For hypertrophy, getting reasonably close to failure appears to be more important than actually reaching the point where another repetition becomes impossible.
That makes failure training another tool in the bodybuilding toolbox.
Use it strategically.
Heavy compound movements can often be stopped slightly short of failure, while machines and isolation exercises provide opportunities to safely push harder. Advanced lifters may also benefit from occasionally using failure to increase training intensity.
But don’t confuse training harder with training smarter.
The goal isn’t to fail as often as possible.
The goal is to provide enough stimulus to grow while managing fatigue well enough to come back and perform again.
Let us know what you think in the comments below. Also, be sure to follow Generation Iron on Facebook, Twitter, and Instagram.
References
Robinson, Z.P., Pelland, J.C., Remmert, J.F., et al. “Exploring the Dose-Response Relationship Between Estimated Resistance Training Proximity to Failure, Strength Gain, and Muscle Hypertrophy: A Series of Meta-Regressions.” Sports Medicine. 2024;54(9):2209–2231. PubMed
Grgic, J., Schoenfeld, B.J., Orazem, J., Sabol, F. “Effects of Resistance Training Performed to Repetition Failure or Non-Failure on Muscular Strength and Hypertrophy: A Systematic Review and Meta-Analysis.” Journal of Sport and Health Science. 2022;11(2):202–211. PubMed
Refalo, M.C., Helms, E.R., Trexler, E.T., Hamilton, D.L., Fyfe, J.J. “Influence of Resistance Training Proximity-to-Failure on Skeletal Muscle Hypertrophy: A Systematic Review with Meta-analysis.” Sports Medicine. 2023;53(3):649–665. PubMed
