Q: It’s hard for me to believe that a few partial reps at the end of a set [a.k.a. X Reps] can do anything measurable for muscle gains. Isn’t doing an additional set just as good or better for muscle growth?
A: At first glance, you’d think so; however, once you understand muscle physiology, you see the enormous muscle-building effects that can occur if you extend a set correctly. It all starts with the size principle of muscle fiber recruitment…
On any set, the low-threshold motor units fire first (slow-twitch fibers), then the medium-threshold motor units take over (mostly fast-twitch high-glycolytic/high oxygenic). Finally, on the last few brutal reps, the high-threshold motor units kick in, which activate the fastest-growing fast-twitch fibers (that’s where the no-pain-no-gain credo comes from).
Unfortunately, on any set to exhaustion, the nervous system craps out before the muscle—it’s short-circuited by lactic acid and/or ATP exhaustion—so you activate very few of those fast-growing fast-twitch fibers.
By forcing the muscle to continue to fire in its strongest position with short partials, like near the bottom of a press or chinup, you extend the set and continue to activate high-threshold motor units and therefore more pure fast-twitch fibers—the ones most conducive to growth.
Yes, X Reps take some grit and will power, but we’ve found that properly performed they can make a big midrange exercise, like dumbbell presses pictured above, three to five times more effective at building muscle. It’s a simple, albeit painful, technique with powerful anabolic consequences.
If you stop at failure, skip the X Reps, and just go for another straight set, you have a somewhat fatigued muscle on that second set. You may activate a few more fast-twitch fibers toward the end of that second set, but you will hit the wall much sooner and may get at only a very few of the important fibers. That’s why bodybuilders who use subfailure training have to do set after set after set—to get at enough of those key fast-twitch fibers to elicit a growth response.
X-Rep partials are simply more effective and efficient—unless you really enjoy doing five or more sets per exercise. We don’t always have time for that because we like to squeeze as much muscle-building stimulation as possible into time-constrained workouts. We’re all about efficiency of effort in the gym, and X Reps are a big part of that.
[An overview of X Reps, along with a basic X-Rep workout is presented in the X-traordinary X-Rep Workout.]
Till next time, train hard—and smart—for BIG results.
—Steve Holman and Jonathan Lawson
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