Best Rep Speed for Muscle Growth

Q: I’m confused about the best rep speed for muscle growth. I’ve read that slow-mo training, like eight seconds up and eight seconds down, can produce good results, but then I see CrossFit trainers moving very fast on the positive and negative of every rep, almost a blur. I’ve also seen some pro bodybuilders, like Jay Cutler, use fairly fast partial-range movements. What’s best for building mass?

A: I’ve discussed a study on ideal rep speed for muscle mass in previous columns. It compared doing sets with a two-to-three-second positive and a two-to-three-second negative—about three up/three down—with sets using a power cadence, which is one second up and three seconds down. The power cadence produced the most mass. [Int J Sports Med. 30(3):200-204; 2009.]

Why would doing power-type sets build muscle more efficiently? Muscle biopsies suggest that it causes more damage to more muscle fibers, leading to a greater degree of protein remodeling in the trained muscle. In other words, the slow lowering caused more muscle damage. But wait—the three-up, three-down group lowered just as slowly, so what gives?

Answer: The slow lowering produced equal muscle damage in both groups, but the power-training group used an explosive turnaround for the one-second positive compared to the slower tempo of the other group. The explosive jolt right at the target muscle’s semi-stretch point—the turnaround from negative to positive, like near the bottom of a bench press—activates significantly more fast-twitch muscle fibers. That’s one reason that doing end-of-set X-Rep partials at the semi-stretch point builds mass quickly.

Keep in mind that the turnaround, where the muscle is stretched, is where injury is most likely to occur, so don’t throw the weight. Use a controlled explosion—no heaving or jerking. The CrossFitters who jerk are asking for trouble. I’ve seen them torquing their shoulders at the bottom of every chinup rep with a hard bounce. Very bad idea. 

As for slow-mo training, doing it every so often—to trigger new sarcoplasmic growth with longer tension times—can be a good tactic, but if you do it exclusively, you can miss a lot of key growth fibers. I prefer X-centric, or negative-accentuated, sets, which still have a one-second lift for turnaround fiber activation but with a slow lowering of six seconds. That produces unique hypertrophic stimulation, as eight X-centric reps would be almost a full minute of tension time. Plus, you get excess microtrauma from the negative emphasis.

What about the pros? They use a variety of rep tempos—and even when they move fairly fast, as Jay Cutler often does, they stay in control. Cutler does higher reps, so the tension time is up around 40 seconds per set. He tends to use partial-range reps to keep tension on the target. Both high reps and partials can produce excellent sarcoplasmic-size increases.

So most of the time I suggest a one-second lift and a three-second lower on most exercises. Some stretch-position moves in the Positions-of-Flexion mass-training protocol may require a slightly slower cadence and more controlled turnaround, as the danger is elevated; for example, flyes for chest, overhead extensions for triceps and stiff-legged deadlifts for hamstrings. When in doubt move slower, never faster.