For decades, an ironclad rule has prevailed in strength training: train to muscle failure – otherwise nothing grows. But recent research shows that this isn't entirely true. A new study, published in 2025 on PubMed , investigated the extent of muscle growth when training close to failure , but not completely to it.
The result: Almost identical hypertrophy – with significantly less exhaustion .
Study Overview
Title & Source
“ Similar muscle hypertrophy following eight weeks of resistance training proximity-to-failure determined by repetitions-in-reserve (RIR) ”
Published 2025, PubMed Central
DOI: 10.1249/JSSM.38393985
The aim of the study
The study investigated whether training to failure (0 RIR) actually leads to greater muscle growth compared to training just before failure (e.g., 2 RIR) .
In short: How close to the limit do you have to get for the muscle to grow?
Design & Process
- Duration : 8 weeks
- Participants : 34 healthy men and women with 1–3 years of training experience
- Exercises : Leg extensions and squats (focus on quadriceps)
- Frequency : 3 sessions per week
- Groups :
- Failure group (0 RIR) – all sets to muscle failure
- RIR group (2 RIR) – Training was ended when there were approximately two repetitions left in the tank.
Measurement : Muscle cross-sectional area (ultrasound), strength gain (1-RM), subjective workload (RPE).
Results: Muscle growth even without total failure
1. Equal hypertrophy in both groups
After eight weeks, both groups showed comparable muscle growth.
→ Average quadriceps growth:
- 0 RIR: +7.9%
- 2 RIR: +7.4%
The difference was not statistically significant.
2. Reduced fatigue at 2 RIR
Participants who trained with two repetitions in the tank reported:
- less muscle pain
- better training frequency
- higher overall performance over the week
3. Same strength gain, but better recovery
Both groups increased their leg extensor strength by approximately +12%.
However, the 2-RIR group recovered faster, which allowed them to complete more volume in the long term.
Interpretation: Muscle building is not an all-or-nothing principle.
The data clearly show:
You don't have to push every set to total muscle failure to achieve maximum hypertrophy.
Muscle growth depends less on whether you completely burn out, but rather on how many effective repetitions you achieve per muscle.
Why this works
-
High voltage is sufficient
The last repetitions of a set generate the greatest muscle tension – even if you end the set 1-2 reps earlier. -
Better recovery = higher total volume
Those who don't completely burn out can produce more high-quality sentences over the course of the week. -
Long-term constant stimulus
This leads to sustainable progress without overtraining or risk of injury.
RIR – the new benchmark for intelligent training
“ Reps in Reserve ” (RIR) describes how many more repetitions you could have done before muscle failure occurs.
Example:
- You do 10 repetitions, but you could do 12 → 2 RIR
- You do 12 and can't do another → 0 RIR
Recommended RIR zones per training goal
|
Goal |
Recommended RIR |
Reason |
|
Muscle building (hypertrophy) |
0–2 RIR |
Maximum tension, high recruitment |
|
Increase in strength |
1–3 RIR |
Clean technology, stable performance |
|
Technique & Volume Training |
2–4 RIR |
Focus on quality & control |
|
Regeneration units |
3–5 RIR |
Blood flow, reduced strain |
This allows training to be precisely controlled without having to push yourself to the limit every time.
Practical application: How to train with the RIR system
1. Choose the appropriate area
Start with 2 RIR per set – that's close enough for stimulus, but safe for technique.
2. Use progressive overload
Increase the weight if you regularly have >3 RIR.
Once you drop to 1-2 RIR, it's time to adjust your weight.
3. Note your RIR perception
After each sentence, write down how many more repetitions you could have done.
This will help you learn to realistically assess your intensity.
4. Prioritize basic exercises
- Squats
- bench press
- deadlift
- Pull-ups
These exercises benefit most from controlled, not complete, exhaustion .
Limitations of the study
- Duration: 8 weeks – long-term effects (> 16 weeks) still unclear
- Only the quadriceps were examined – other muscle groups could react differently.
- The subjects were young adults – generalizability to older people or beginners is limited.
- Motivation and mental stress (at 0 RIR) were not quantitatively measured.
Nevertheless, the study provides strong evidence that RIR-based training is an efficient, safe and scientifically sound method for building muscle.
Conclusion: Muscle building is also possible with reserves.
This new study dispels an old myth:
You don't always have to go to muscle failure to build muscle.
Training with 1-2 repetitions in the tank is perfectly sufficient to achieve comparable gains in strength and hypertrophy – with less fatigue and more training quality.
Less pain, same gains – that's intelligent training.
Source: PubMed, 2025 – DOI: 10.1249/JSSM.38393985
Atletica – Scientific training, practical implementation
At Atletica you'll find everything you need to design your training according to the RIR principle:
- Adjustable weight benches & racks , ideal for precise progression tracking
- Olympic barbells & weight plates for controlled load
- Dumbbells & Kettlebells , perfect for variable intensity
- Digital timers and training apps, compatible with Atletica accessories
Train smarter, not harder – with Atletica .
