This Study Completely Changed How I Train To Failure

Main Ideas and Findings

What “Reps in Reserve” Means

Reps in reserve (RIR) is the number of additional repetitions someone believes they could have completed before reaching failure.

• 0 RIR: No further rep is possible.
• 1–2 RIR: The set ends with one or two reps still possible.

The speakers emphasize that RIR and training to failure are not opposing approaches. Both can be used in a program, and the best choice depends on the person, exercise, and workout context.

The 2024 Failure-versus-RIR Study

Dr. Martin Refalo described an eight-week study comparing training to failure with stopping short of failure in experienced lifters.

• Participants: 18 resistance-trained adults—12 men and six women—with an average of about 7.7 years of training experience.
• Design: Each participant trained one leg to momentary failure and the other to a target of 1–2 RIR. This within-person design helped compare the conditions while reducing differences between participants.
• Training: Participants trained their legs twice weekly, using the leg press followed by the leg extension. Training was supervised, and the study controlled nutrition.
• Checking RIR accuracy: Before the study, participants called out when they believed they had reached an RIR target, then continued to failure. Their estimates were fairly accurate on average, especially close to failure. This supports the idea that experienced trainees can judge low RIR reasonably well, though it does not establish that they were equally accurate on every set throughout the study.
• Measuring growth: Muscle thickness was measured by ultrasound before and after the intervention. Measurements were repeated to check reliability and reduce the chance that temporary post-training swelling would be mistaken for muscle growth.

Main result: Overall quadriceps growth was similar between the leg trained to failure and the leg trained at 1–2 RIR. The researchers also observed small, exploratory differences between individual quadriceps muscles, but those findings were minor and need further investigation.

The study also found that:

• The failure condition involved greater repetition loss across sets.
• Despite that, total volume load was similar between conditions.
• Repetition loss became less pronounced over the eight weeks, suggesting that people may adapt to the fatigue produced by a repeated training stimulus.

What the Study Means for Training

For hypertrophy-focused exercises, Refalo’s practical recommendation is a “strike zone” of 0–2 RIR: most working sets should end somewhere between failure and two reps short of it.

Training to failure is not required on every set to make progress. Stopping at 1–2 RIR can produce comparable growth in the conditions studied. Failure can still be useful because it:

• Gives trainees experience with what true failure feels like, helping them calibrate their RIR estimates.
• May provide additional stimulus on selected sets.
• Can be used more often by people who tolerate it well.

Jeff Nippard and Refalo discuss taking an early set to failure as one possible strategy. Because the trainee is fresh, that set may be especially productive; it can also serve as a reference point for estimating RIR on later sets. Their broader advice is to use whichever approach supports good performance and consistency within the 0–2 RIR range.

Fatigue and Exercise Selection

The discussion cautions against treating fatigue as a simple, universally harmful quantity.

• Failure training produced more repetition loss, but the study did not find worse overall quadriceps growth from it.
• Fatigue can refer to different things, including reduced performance between sets, incomplete recovery between workouts, or cardiovascular, respiratory, and mental strain. These should not be treated as interchangeable.
• Excessive fatigue can matter if it interferes with training quality, recovery, or someone’s ability to maintain a program. Its importance depends on factors such as schedule, sleep, nutrition, training volume, and recovery capacity.
• As a workout includes more exercises and sets, Refalo suggests being more selective about where failure is used. Individual tolerance varies considerably.
• Exercise order and muscle function may also affect results. In the study, the leg press came before the leg extension. The speakers suggest this may have influenced how much fatigue different quadriceps muscles carried into the later exercise. They describe this as a possible explanation for small muscle-specific differences, not a confirmed result.
• Mental factors can affect performance too. The speakers mention research suggesting that scrolling social media during a workout may reduce performance, while relaxing beforehand may help. They argue that such factors can matter more than small differences in muscular fatigue between failure and near-failure sets.

How Close to Failure Is Close Enough?

The study directly tested 1–2 RIR, not more distant targets such as 3–4 RIR.

Broader meta-analytic evidence discussed in the episode suggests that, on average, sets closer to failure tend to produce more hypertrophy. However, the studies differ in participants, methods, training protocols, and definitions of failure.

The speakers agree that the exact threshold remains uncertain. A future study comparing failure with 3–4 RIR could help clarify how far from failure someone can stop without meaningfully reducing growth.

They recommend judging progress over time rather than trying to assess muscle growth from day to day. Performance improvements that emerge over weeks can indicate that a training approach is working; if progress stalls, training variables can be reconsidered.

Low-Volume Training Study

The episode also discusses a 2025 study comparing a single set per exercise taken to failure with a single set stopped at about 2 RIR.

• Participants were resistance-trained, and the protocol involved only a handful of sets per muscle each week.
• Both conditions produced muscle growth, with broadly similar outcomes.
• Some results trended in favor of failure, but the speakers caution against treating those small directional differences as conclusive.
• The findings suggest that even very low-volume training can be effective in the short term, including when sets stop around 2 RIR. They do not establish that the same rate of growth would continue indefinitely or outside a supervised study.

Refalo’s Untested Programming Idea

When asked for a belief he considers plausible but lacks direct data to confirm, Refalo proposed using indirect work to increase how frequently a muscle is trained without greatly lengthening workouts.

His example is glute training: a four-day program could include two quad-focused days that also involve the glutes indirectly, alongside two posterior-focused days that train the glutes directly. He says this approach has worked well in his coaching experience, particularly for clients pursuing glute growth, but notes that the idea lacks direct research support.

Similar logic might apply to other muscles—for example, chin-ups contributing to biceps work or close-grip bench presses contributing to triceps work. Recovery still matters; higher frequency is useful only if the trainee can tolerate it.

Speakers and Sources Featured

Speakers

• Jeff Nippard — host and interviewer.
• Dr. Martin Refalo — exercise scientist, coach, and guest.

Research and Other People Discussed

• Refalo’s 2024 study comparing eight weeks of resistance training to momentary failure versus 1–2 RIR in resistance-trained participants.
• A meta-analysis on proximity to failure and hypertrophy, discussed as part of a research group including Zack Robinson.
• A 2025 single-set failure-versus-RIR study, led by Tom Herman and associated with Brad Schoenfeld’s research group.
• Research on mental fatigue and workout performance, including the effects of social-media use during training and relaxing before exercise.
• Greg Nuckols, discussed in relation to the idea of taking an early set to failure.
• Mike Israetel, Dorian Yates, and Mike Mentzer, mentioned as examples of different training philosophies.