Why Slow Eccentric Phases Won't Build a Lot of Muscle: A Deep Dive into Muscle Physiology
· Sabrina Wescott
Last updated: October 15, 2026
The quick answer: Slowing down the lowering (eccentric) phase of a lift isn't the muscle-building secret it's often made out to be. Most of the stimulus for muscle growth comes from hard, effortful lifting, especially as you get close to failure, and that happens mainly in the concentric (lifting) phase. Controlled lowering is still useful for form and safety, but the bigger levers for muscle growth are effort, progressive overload, volume, and recovery.
"Slow down the negative" is one of the most repeated tips in fitness. Plenty of influencers will tell you a 4-second lowering phase is the key to growth. But muscle physiology tells a more nuanced story. This article is based on an episode of The Chris and Paul Show, where Paul Carter and Chris Beardsley, who focus on muscle physiology and biomechanics, break down why slow eccentrics won't build as much muscle as people think.
Concentric vs Eccentric: The Basics
| Concentric phase | Eccentric phase | |
|---|---|---|
| What happens | The muscle shortens as you lift | The muscle lengthens as you lower |
| Example | Curling a weight up | Lowering the weight back down |
| Muscle activation | Higher: more fibers have to work | Lower: the muscle produces more force with less activation |
| Soreness | Less next-day soreness | The main driver of next-day soreness |
The idea behind slow eccentrics is simple: lower slowly, increase time under tension, grow more muscle. The problem is that time under tension alone isn't what drives growth.
Why Slow Eccentrics Don't Build Extra Muscle
1. Your muscles work less during the lowering phase
During the eccentric phase, a muscle can produce roughly twice the force with about half the activation compared to the concentric phase. Your nervous system is simply more efficient when lowering. That means fewer muscle fibers, especially the high-threshold fibers with the most growth potential, are being pushed hard while you lower a weight slowly.
2. Effort is what recruits the fibers that grow
According to Beardsley and Carter, the biggest stimulus for growth comes when your muscles have to work hard and slow down involuntarily near failure, because that's when the largest, most growth-responsive motor units are fully engaged. That happens mainly as you struggle to lift, not as you lower. In the podcast, they estimate the concentric phase accounts for the large majority of the growth stimulus in normal training, with the eccentric phase contributing a smaller share.
3. Older studies created the confusion
The belief in slow eccentrics traces back partly to research on eccentric overload, where more weight is used on the lowering phase than the lifting phase. That's a very different stimulus from just lowering a normal weight slowly. In typical training, there's no extra resistance on the way down, so those results don't directly apply.
So Should You Skip Controlled Lowering?
No. Controlling the weight on the way down still matters:
- Better form. A controlled lowering phase keeps you in a safe position through the full range of motion.
- Injury prevention. It prevents jerky, uncontrolled reps.
- Specific goals. Eccentric overload has a place in some advanced and rehab programs.
The takeaway isn't that eccentrics are useless. It's that dragging out the lowering phase isn't a growth hack, and it costs you energy and recovery you could spend on harder lifting.
What Actually Builds Muscle
The real priorities
- Effort: Take your working sets close to failure.
- Progressive overload: Gradually increase the resistance, reps, or sets over time. Here's how progressive overload works.
- Enough volume: In the podcast, the hosts suggest that a few hard sets per muscle, a couple of times a week, is enough for most people to grow.
- Recovery: Sleep, protein, and rest days. Muscles grow while you recover.
That's good news for busy people. Shorter, harder workouts can be very effective, and you don't need to spend half of every rep lowering slowly.
Where Concentric-Focused Training Fits In
This is exactly the principle behind MAXPRO. Both MAXPRO machines are concentric: you feel resistance as you lift or pull, and the cable returns smoothly on the way back. That means you put your effort where most of the growth stimulus is, with less of the muscle damage and next-day soreness that heavy eccentrics cause. Less soreness means faster recovery, which makes it easier to train more often.
The MAXPRO SC: up to 300 lbs of concentric cable resistance.
The MAXPRO SC goes up to 300 lbs of resistance with dual cables for heavy two-handed lifts, bench compatible, and weighs under 10 lbs. The MAXPRO Air weighs 2.85 lbs, goes up to 125 lbs, and has a 12-foot cable for single-arm, athletic, and travel training. Both connect to the MAXPRO Coaching App, no subscription required.
The research backs it up. In a 12-week peer-reviewed study, UCLA researchers found people training with MAXPRO built strength equivalent to traditional weights and cable machines, completing nearly the same training volume. Read the UCLA study breakdown →
The Bottom Line
Slow eccentrics won't unlock dramatic muscle growth. Control the weight for good form, but put your real effort into hard, progressive lifting, enough weekly volume, and recovery. For the full deep dive, listen to the Chris and Paul Show episode "Why Eccentrics Will NOT Build a Lot of Muscle."
Eccentric Training: FAQ
Do slow eccentrics build more muscle?
Not significantly. Slowing down the lowering phase of a normal lift adds time under tension but doesn't add much growth stimulus compared to hard, effortful lifting.
What is the difference between concentric and eccentric?
Concentric is the lifting phase, where the muscle shortens. Eccentric is the lowering phase, where the muscle lengthens.
Can you build muscle with concentric-only training?
Yes. Concentric training creates the effort and tension muscles need to grow, with less soreness. A UCLA study found MAXPRO's concentric training built strength equivalent to traditional weights.
Is eccentric training bad?
No. Controlled lowering helps with form and safety, and eccentric overload has a role in some advanced and rehab programs. It just isn't the main driver of muscle growth in normal training.
Why does eccentric training make me so sore?
The lowering phase causes more microscopic muscle damage, which is the main source of next-day soreness. Concentric-focused training typically causes much less.
Related: Benefits of Engaging Fast-Twitch Muscles · What Is Progressive Overload?
