Key Takeaways on Slow Eccentrics for Muscle Growth
- Slow eccentrics for muscle growth do not build more muscle if total training volume is similar.
- Muscle growth was virtually identical whether lifters lowered the weight in one to two seconds or three to six seconds.
- If your goal is size, you can lift and lower with control — but exaggerated slow eccentric training is not required.
- Evidence does not support the idea that slow lowering phase training provides superior hypertrophy.
- Current research shows no clear advantage of eccentric training for muscle growth when volume is equated.
Have We Been Overcomplicating Slow Eccentrics for Muscle Growth?
For years, lifters have been told to emphasize the eccentric contraction — the lowering phase — by taking three to five seconds to bring the weight down. Coaches have promoted slow eccentric training as essential. Bodybuilding articles have framed slow lowering phase training as a shortcut to hypertrophy.
But here is the real question: do slow eccentrics for muscle growth actually work?
A new systematic review and meta-analysis by Christian Houmann Amdi and Andrew King, published in the Journal of Sports Sciences in 2025, directly tackled that question. The paper, titled “The effect of eccentric phase duration on maximal strength, muscle hypertrophy and countermovement jump height”, analyzed nine controlled training studies to determine whether eccentric training for muscle growth improves hypertrophy when the lowering phase is prolonged.1
What they found challenges years of gym folklore.
And if you care about maximizing muscle growth without wasting energy on unnecessary techniques, this research matters.
Why Slow Eccentrics for Muscle Growth Became Popular
The eccentric phase is the lowering portion of a lift. When you descend into a squat or lower a dumbbell during a curl, that is the eccentric portion.
The theory behind slow lowering phase training seems logical:
More time under tension equals more growth.
Because muscles can produce more force eccentrically, advocates of eccentric training for muscle growth argue that prolonging this phase increases stimulus. This belief helped popularize slow eccentric training in gyms worldwide.
Previous reviews showed mixed results. Some studies suggested that extremely slow repetitions, meaning more than ten seconds per rep, actually produced worse muscle growth compared to moderate tempos.2
Similarly, Kojić and colleagues examined untrained men and women over seven weeks of arm curl training using either a one-second or four-second lowering phase.3 Both groups trained to muscular failure. Again, both groups gained muscle, and once again, there was no significant difference in hypertrophy between the two tempos. Even in beginners — who typically grow rapidly — slow eccentrics did not produce additional muscle growth.
Azevedo and colleagues provided even tighter control by using a within-participant design. 4Each participant trained one leg with a slower eccentric phase and the other leg with a faster one. Over eight weeks of unilateral leg extension training, both legs increased in muscle thickness. However, there was no meaningful difference between slow and faster eccentric conditions. Because each individual served as their own control, this strengthens the conclusion substantially.
That is why this new review is important. Instead of mixing everything together, the authors only included studies where the lowering speed changed, but everything else stayed controlled.
In other words, they isolated the variable that most lifters obsess over: how slowly you lower the weight.
How the 2025 Review on Slow Eccentrics for Muscle Growth Was Conducted
Amdi and King followed strict research guidelines. They searched multiple major databases and screened more than three thousand studies before narrowing it down to nine high-quality experiments that met their criteria.
Across those nine studies:
- 166 participants trained.
- About half were trained lifters.
- Most trained twice per week.
- Study length ranged from four to twelve weeks.
- Exercises included squats, leg presses, leg extensions, and arm curls.
The comparison was simple:
- Short eccentric duration: one to two seconds lowering the weight.
- Long eccentric duration: three to six seconds lowering the weight.
Importantly, total volume was matched.
This is critical when evaluating slow eccentric training, because volume often drives hypertrophy more than tempo alone.
By isolating eccentric duration, the authors were able to directly test whether slow eccentrics for muscle growth outperform controlled, moderate tempos.
The researchers then combined all the data using advanced statistical analysis to determine whether one approach produced more muscle growth.
The Results: Muscle Growth Was Essentially the Same
Here is the bottom line.
There was no meaningful difference in muscle growth between shorter and longer lowering phases.
The average effect size for hypertrophy was 0.05. That number is extremely small. Practically zero. The confidence intervals crossed into both directions, meaning neither approach clearly outperformed the other. Despite widespread promotion of slow lowering phase training, the data did not support a hypertrophy advantage.
In simple terms:
Lowering the weight in one to two seconds built just as much muscle as lowering it in three to six seconds.
That is a direct contradiction to the long-standing belief that slow eccentrics are superior for size.
Now, to be fair, the review also looked at strength and jump performance. Interestingly:
Slower eccentrics may slightly benefit strength in trained lifters.
Faster eccentrics improved jump performance more than slower ones.
But for hypertrophy? No advantage.
Why Slow Eccentrics Do Not Magically Build More Muscle
If slow eccentrics for muscle growth increase time under tension, why is there no added growth?
Because when total workload is similar, muscle fibers likely receive sufficient stimulus regardless of whether the eccentric phase lasts one second or four.
In fact, slow eccentric training often forces lifters to reduce load or perform fewer reps.
That reduction can offset any potential benefit of prolonged tension.
Muscle growth appears to respond more strongly to:
- Total volume
- Mechanical tension
- Proximity to failure
- Progressive overload
Not simply dragging out the eccentric.
What This Means for Eccentric Training for Muscle Growth
Let’s be honest. Many lifters spend mental energy obsessing over tempo counts.
“One… two… three… four…”
Meanwhile, they could be focusing on progressive overload, consistency, and total training quality.
This study suggests that you do not need exaggerated slow eccentrics to maximize growth. Controlled, strong repetitions performed with intent are enough. When volume is matched, slow eccentrics for muscle growth show no advantage. You do not need five-second negatives for effective eccentric training for muscle growth.
That does not mean you should drop weights recklessly. Control still matters. But there is a difference between control and unnecessary slowness.
If you lower a 60-kilogram dumbbell (about 132 pounds total across two hands) in one to two seconds under control, that is sufficient.
You do not need to stretch it to five seconds, hoping for extra hypertrophy.
Practical Applications: What Should You Do?
1. Stop Overthinking the Lowering Phase
If your goal is muscle growth, focus on:
- Training hard.
- Progressively adding weight or repetitions.
- Accumulating sufficient weekly volume.
- Lower the weight under control, but do not artificially slow it down.
2. Prioritize Volume and Effort
Muscle growth responds to total workload and proximity to failure. Whether you lower in one second or four seconds appears secondary when the volume is similar.
3. Use Slow Eccentrics Strategically
There may still be uses for slower lowering:
- Learning technique.
- Reducing joint stress.
- Improving control in beginners.
But do not assume it will automatically build more muscle.
Conclusion: Do Slow Eccentrics for Muscle Growth Work?
For years, lifters have been told to lower the weight slowly — three to five seconds — to maximize muscle growth. However, this comprehensive 2025 meta-analysis by Amdi and King shows that when total training volume is similar, slower eccentrics do not produce greater hypertrophy (Amdi & King, 2025).
If you lower the weight under control in one to two seconds, you can build just as much muscle. The real drivers of growth remain consistent training, progressive overload, and sufficient volume.
So the next time someone tells you that five-second negatives are mandatory for size, you can confidently respond: The evidence does not support that.
References
1 Amdi, C. H. & King, A. The effect of eccentric phase duration on maximal strength, muscle hypertrophy and countermovement jump height: A systematic review and meta-analysis. Journal of Sports Sciences 43, 2447-2464 (2025). https://doi.org/10.1080/02640414.2025.2535198
2 Schoenfeld, B. J., Ogborn, D. I. & Krieger, J. W. Effect of repetition duration during resistance training on muscle hypertrophy: a systematic review and meta-analysis. Sports Med 45, 577-585 (2015). https://doi.org/10.1007/s40279-015-0304-0
3 Kojić, F. et al. Effects of resistance training on hypertrophy, strength and tensiomyography parameters of elbow flexors: role of eccentric phase duration. Biol Sport 38, 587-594 (2021). https://doi.org/10.5114/biolsport.2021.99323
4 Azevedo, P., Oliveira, M. G. D. & Schoenfeld, B. J. Effect of different eccentric tempos on hypertrophy and strength of the lower limbs. Biol Sport 39, 443-449 (2022). https://doi.org/10.5114/biolsport.2022.105335
