Guide/Exercises
The exercises that actually train fast-twitch
An exercise trains fast-twitch fiber if it has one of two properties: a load heavy enough that the bar moves slowly on its own, or a movement fast enough that slow fibers cannot keep up. Sprints, jumps, throws, sled work and heavy compound lifts qualify. Machines at moderate load and steady cardio mostly do not.
Not a workout. A way of telling, for any exercise you already do, whether it reaches the fiber you are trying to reach.
What makes an exercise a fast-twitch exercise?
One rule, and it is worth understanding rather than memorizing, because it lets you judge any exercise you come across.
Muscle fibers are recruited in order of size, smallest first. The slow fibers take everything they can handle, and the fast ones only join in when the demand exceeds what the slow ones can produce. There are exactly two ways to create that demand.
Force: a load heavy enough that the slow fibers cannot move it, so the fast ones are called in on the first rep. Speed: a movement fast enough that the slow fibers cannot contract quickly enough to contribute, whatever the load is.
That is the whole test. Everything below either creates one of those two conditions or it does not.
The movements that qualify
- 01
Sprinting
The cleanest example there is, because there is no way to sprint slowly. Maximal force, produced fast, through the glutes and hamstrings, at levels a gym cannot easily reproduce.
- 02
Hill sprints and sled pushes
The same demand with a lower ceiling on speed, which is why they are the sensible place to start. The hill caps how fast you can go, so it caps how much trouble you can get into.
- 03
Jumps
Broad jumps, vertical jumps, box jumps. Bodyweight, but the ground contact is brief and the force is high, which is precisely the condition. Quality collapses quickly, which is why the sets are short.
- 04
Medicine ball throws
The upper-body equivalent of a jump, and the rare way to train the torso and shoulders explosively without decelerating at the end of the range.
- 05
Heavy compound lifts
Squat, deadlift, bench, overhead press, loaded to where the bar genuinely moves slowly. Here it is the force route rather than the speed route, and the intent to move it fast still matters.
- 06
Olympic-style pulls
Cleans, snatches, high pulls. Heavy and fast at the same time, which is why they are efficient, and technical enough that they are not the place to start.
- 07
Kettlebell swings
A hip snap under load. Accessible, low skill ceiling compared to the lifts above, and one of the easier ways to add real speed work to a gym session.
What does not train it, and why
Steady cardio, by definition. Low force sustained over time is the exact opposite condition, and it is what slow fibers exist for.
Machine work at moderate loads, mostly. The load is not high enough to require the fast fibers and the movement is usually deliberately controlled, which removes the speed route as well. A leg press taken to genuine failure does get there eventually, at the end of the set, when the slow fibers have run out.
Sets of ten at a comfortable weight moved at a comfortable tempo. This is the big one, because it is what most people do most of the time and it feels like work. Effort is not the same as demand.
None of that makes those exercises bad. They build muscle and they have their place. They simply do not solve the problem this site is about.
How do you tell if you are actually reaching it?
Ask what would happen if you tried to do one more rep, or one more effort, at the same quality. If the answer is that you could keep going for a while, you are in slow-fiber territory.
The other tell is fatigue behavior. Fast-twitch work degrades fast and obviously: the fourth sprint is slower than the first, the sixth jump is lower than the second, the bar speed drops off a cliff. If your fifth set looks exactly like your first, the fast fibers are not the ones doing the work.
That is also why these sessions are short. Once the quality has gone, the fiber you came for has stopped participating, and everything after that is volume for something else.
Where does this work go in a session?
First, on fresh legs, before anything that will tire you out. Explosive work done tired is not explosive work, it is just tiring.
Heavy strength work goes next, while you can still produce real force. The accessory volume, the machines, the conditioning and everything that builds shape goes last, where being tired costs nothing.
This page is a way of judging exercises, not a program. What to do, in what order, for how long, is what the twelve weeks are for.
Questions on this
What is the single best exercise for fast-twitch?
Sprinting, because it is the only one where you cannot accidentally do it slowly. If sprinting is not available, hill efforts or a sled are the closest substitutes, and heavy compound lifts cover the force half.
Can bodyweight exercises train fast-twitch?
Yes, through the speed route. Jumps and throws are bodyweight or near it and they qualify easily, because the force is high and the contact is brief. Slow bodyweight circuits do not.
Do I need weights at all?
Not to reach the fiber. Sprints, hills and jumps get you there on their own. Weights add the force route, which is a different quality and worth having, but the speed route is free.
Are high-rep sets to failure enough?
They reach type II at the very end, once the slow fibers are exhausted, which is why training to failure works at all. It is a slow, expensive route to a few effective reps compared with simply making the load heavy or the movement fast.
How many of these should I do in a week?
Two or three sessions containing this kind of work, not more, because they are recovered from like the high-force efforts they are. The exact split is what a program is for.
Where the numbers come from
- Experimental Gerontology, 2013 (PMID 23425621)
Muscle biopsies from 25 healthy young men, average age 23, and 26 healthy older men, average age 71. Type II fibers were 29% smaller in the older group; the difference in type I fibers was not statistically significant. The same older men then trained for six months, after which their type II fiber size had increased by 24%.
Read next
The fiber you stopped asking for
What type-II muscle fiber is, why it fades before anything else, and the training that actually asks for it. Written plainly, with no hacks and no supplements.
Sprinting after 30, and why it changes how you look
Does sprinting build muscle? What sprinting does that cardio does not, and how to start again when you have not run flat out in years.
What hybrid training actually is
Training for strength and endurance at once. What the term means, whether the two actually fight each other, and how to run both without wasting either.
The program is these, in an order, for twelve weeks.
$77 once. All four programs, for life. First 5,000 members.