T Nation

Conflicting Fast Twitch Messages


I've read that prolonged eccentrics increases fast twitch fibers. I also read that SPEED training, such as lifting the weight real fast for the concentric and eccentric portion of the exercise, increases fast twitch fibers. Which one is better? Isn't this conflicting? fast and slow eccentrics are increasing fast twitch fibers? Seems like opposites.

I'm thinking eccentrics increases fast twitch SIZE and makes it STRONGER, but the speed training makes the fast twitch fibers fire more quickly? That's the best guess I have...

I apologize ahead of time if this answer is easily accessible, I looked around for a good 40 mins to find a definite answer and found none.

Any help to clarify this?


Sounds like a study needs to be done on this specific question...


Just about any exercise will train, and to some degree hypertrophy the fast twitch fibers.

What speed training does, as plyos and olympic lifts, is train your nervous system to increase rate of force development. Recruit as many motor units as possible in a near simultaneous time.


train to be strong not for fiber type

or youll end up like type2B




With everyone hating you? But the OP hasn't posted anything retarded and annoying yet.

OP, as far as I can gather fast twitch fibers are used when larger loads are encountered (anywhere about about 40% of your max give or take for personal make-ups)
It would make sense that eccentric training is good for them because it allows greater weight for longer time to be used, while plyo training would allow greater force production to be trained. As said above this is very much also a part of neural efficiency. Don't forget to train for strength in the concentric movement too, still very important no matter what you're training for.
Unless you're a marathon runner, you're not a marathon runner are you?


nope, basketball player. I have been using prolonged eccentrics for the last 6 months in my training because everywhere I read an article it said it was great for muscular damage and fast twitch fibers. Maybe I should just switch it up just for the sake of change.


Yeah i was kidding about the marathon runner, if you were you wouldn't even be thinking about fast twitch fibers. I would definitely switch it up for the sake of change, if your gains have slowed or stopped especially. You can always divide your training into strength training and plyometric training days of course, getting the best of both worlds.

I wouldn't think doing nothing but plyo for any extended period of time would be great for you.


also guys...

what do you guys think of this T-Nation article


i thought prolonged eccentrics got you more stronger, and more bigger

too much conflicting information... will someone who knows what he's doing please clarify this?


Generally as a muscle is required to generate greater force, there will be a concomitant increase in the number of high threshold motor units that are recruited.

So for a concentric action, that means the more quickly the load is accelerated (requiring greater force), the more fast twitch motor units will be recruited.

However, for an eccentric action the resultant force will be gravity/elastic recoil/whatever. This means that the muscle must generate contractile force in opposition to that, decelerating the load. Greater deceleration requires greater force, which will typically result in greater recruitment of fast twitch units.


The way the nervous system recruits motor units in the 2 muscle actions is distinct. The size principle only applies during concentric efforts. During eccentrics there is not an ordered recruitment of fibres from slow --> fast, but what appears to be a preferential recruitment of fast twitch fibres.

For that very reason I wouldn't over think the use of eccentrics. So long as you make a concerted effort to control the load during the yielding phase you'll probably get sufficient stimulus.

As far as speed strength/ strength speed- what you lift with is what you get better at. The loads you train with are the ones you get the greatest power adaptations in. So all you have to do is pick the load that applies most specifically to your goal and train accordingly.


the size principle applies to eccentrics.. pretty much every recent study has proven preferential recruitment to be bunk.. with EMS it is possible apparently.

here's a review study, there's alot more recent studies on this topic:


Literature examining the recruitment order of motor units during lengthening (eccentric) contractions was reviewed to determine if fast-twitch motor units can be active while lower threshold slow-twitch motor units are not active. Studies utilizing surface electromyogram (EMG) amplitude, single motor unit activity, spike amplitude-frequency analyses, EMG power spectrum, mechanomyographic, and phosphocreatine-to-creatine ratio (PCr/Cr) techniques were reviewed. Only single motor unit and PCr/Cr data were found to be suitable to address the goals of this review. Nine of ten single motor unit studies, examining joint movement velocities up to 225°/s and forces up to 53% of a maximum voluntary contraction, found that the size principle of motor unit recruitment applied during lengthening contractions. Deviation from the size principle was demonstrated by one study examining movements within a small range of low velocities and modest forces, although other studies examining similar low forces and lengthening velocities reported size-ordered recruitment. The PCr/Cr data demonstrated the activation of all fibre types in lengthening maximal contractions. Most evidence indicates that for lengthening contractions of a wide range of efforts and speeds, fast-twitch muscle fibres cannot be selectively recruited without activity of the slow-twitch fibres of the same muscle.

"As far as speed strength/ strength speed- what you lift with is what you get better at. The loads you train with are the ones you get the greatest power adaptations in. So all you have to do is pick the load that applies most specifically to your goal and train accordingly. "

well, if you want to jump squat 135 and you squat 225, then it would be misleading to simply train only within that range (lighter weights).. if you end up squatting 335, then you'll be able to throw 135 around alot easier than if you squatted 225.. so here, the carry over in explosive strength from improving maximal strength would prove beneficial.

maybe i misunderstood your comment, or took it wrong.



Thanks for the abstract mate I'll definitely take a look. A lot of my understanding of eccentrics comes from Thibs' methods of strength training book and one of the strength coach presentations by Brijesh Patel, but obv these resources are a few years old.

From an anecdotal stand point though I think the soreness experienced from eccentrics may indicate selective recruitment. A fewer number of motor units being recruited for a given level of force is going to create greater mechanical damage in those fibres, which may affect soreness. I'm just thinking out loud here...

Anyway, with regard to power output and loading, as I understand it the principles apply in a relative sense. Say you and I both squat 225 for max. You train jump squats with 100, I train jump squats with 135. If the test is jump squat performance with 135, in all likelihood I will perform better.

But in absolute terms, the higher my max strength is, the less % of max a given load will be. And given the inverse relationship between intensity and velocity, that is going to correspond to a higher velocity and power output for sure. So yes in absolute terms, max strength is where it's at. But it may be sensible to emphasise specific load/velocity training at points in the training year for certain events e.g. the throws in athletics.

Now enough of this polite debate, this a forum for getting hawt abz bra.