Does lifting slower build more muscle?
Barely — reps anywhere from half a second to about 8 seconds long build roughly the same amount of muscle. Going much slower than that usually just means doing less total work, not more growth.
Slow, controlled reps get pitched as the secret to more time under tension, more muscle damage, more growth. It’s a tidy story, and it mostly falls apart under testing. When two groups do the same total work — same weight, same number of hard sets — rep speed turns out to be almost beside the point.
That’s not one lucky study. A 2015 meta-analysis pooling repetition durations from 0.5 to 8 seconds found similar hypertrophy across the board. A 2025 update, with more studies and sharper statistics, agreed: tempos averaging about 1 second per rep versus about 3.5 seconds per rep produced a trivial difference in muscle gained, if anything slightly favoring the faster group. The one place tempo bites is the extreme end — reps stretched past 10 seconds tend to underperform.
Why slow often means less work
Super-slow reps force lighter loads, since you have to control the weight for many seconds instead of letting momentum help — which can undercut recruitment of the motor units that drive growth. It also shrinks total volume: one study found lifters completed 44% fewer reps at a slow 6-0-4-0 tempo than at a brisk 2-0-2-0 tempo in the same session. Time under tension went up; volume load went down. And volume load, not time under tension, is what tracks with hypertrophy across the literature. Slow lifting isn’t harmful, it’s just an easy way to quietly do less work while it feels like more.
The eccentric question
Some researchers zoom in on just the lowering phase, since eccentric loading has its own damage and tension profile, and a few small trials show an edge for slower eccentrics in specific muscles. But the newest dedicated meta-analysis on eccentric duration, from 2025, found no meaningful hypertrophy difference between shorter and longer eccentric phases — only a possible strength edge for longer eccentrics in trained lifters under matched volume. Promising lever, not a proven one.
Pick a tempo you can control without turning every set into a grind, protect your total volume, and stop treating rep speed as a growth dial. If you want to experiment, the lowering phase is the more interesting knob to turn — just don’t expect it to remake your physique on its own.