T Nation

Zatsiorsky, RE, and HTMUs


Regarding the repeated effort method, does Zatsiorsky state that the high threshold motor units are recruited in the FINAL reps leading to concentric failure, this "maximum tension/force in a fatigued state"?

I thought the whole concept behind RE was that the fatigue requires that HTMUs jump in to complete the action, even if the load and previous reps did not initially warrant it. (I have not read Zatsiorsky, so I'm not sure if I've got this correct.) I am unsure, however, as this would go against the size principle.


Why don't you go buy his books? It will do you a lot better than reading Internet articles and forum responses:

You'll also see that much of what you read is unattributed Zatsiorsky.


The Repeated Effort Method is never used to recruit the highest HTMUs - that's what the Maximal Effort Method is for. The final reps leading to concentric failure (RE Method) yield myofibrillar hypertrophy. Buy the book!


"In the early seventies, strength physiologist Zatiorsky suggested that all sets should be completed to failure, plus one more. HTMUs can be recruited in such bodybuilding methods sets."

"If training to failure doesn't ensure full motor-unit stimulation within a muscle, not taking a set to positive muscle failure (the point where a technically correct full repetition can't be completed) is even less effective since it won't fatigue the HTMUs as much."

"The Repetitive Effort Method: The high threshold/most powerful motor units can also be recruited as a last alternative even if the external load is apparently too light to warrant their activation. This occurs when the effort lasts long enough (while still being relatively intense) so that the amount of fatigue requires the activation of the powerful motor units to be able to complete the action. We're talking about performing relatively long sets (8-15 reps, time under tension of around 40-70 seconds) to muscle failure."

"HTMUs are recruited when the external demand is high RELATIVE the the internal capacity. It's not so much about how heavy the load is, but rather how heavy the load is compared to the amount of force your muscle can produce.

If the difference between muscle force potential and load demand is large, you don't need to recruit the HTMUs. If the difference is small then you'll recruit the HTMUs. The thing is that muscle force potential is not fixed. As you get fatigued (or as metabolites from physical work accumulate in your muscle) the force production potential of the muscle decreases. As this potential decreases the difference between force potential and load gets smaller, hence the recruitment of HTMUs."

DE also recruits HTMUs

That's debatable. At any rate, ME can also hypertrophy the myofibrils.

Myofibrillar and sarcoplasmic hypertrophy can occur at all rep ranges.

I've been intending to, but in the meantime I thought I'd see if I could find someone who could tell me what Zatsiorsky specifically stated.

At any rate, if this were the only thing I wanted to know(it's not), I sure as hell wouldn't spend over $40 to find out. The text isn't exactly cheap.


The Repeated Effort Method is never used to recruit the highest HTMUs - that's what the Maximal Effort Method is for.

Zatsiorsky doesn't contradict Henneman at all. The slow and "medium" MUs become completely exhausted so they are no longer doing work when the faster HTMUs are activated.

Yes, hypertrophy occurs across all rep ranges, but the high activation rate of the highest HTMUs - which are the minority in terms of recruitability via the nervous system and availability in muscle tissue - means that muscles do less 'work'. This translates into far less hypertrophy in a given set using the ME method. Hence the widespread successful real-world application of 8-12 rep set schemes.

Obviously shortening rest intervals yields higher levels of hypertrophy. However, the RE can never recruit the faster MUs activated via the ME method. (Think the All or Nothing Principle, not the Size Principle)

I'm curious as to whether you're looking for some set of specific, direct quotes from Zatsiorsky or? I can help you just let me know what you have in mind. Naturally I'm not going to scan the book for you, and I really recommend that if you have even a passing interest in the biomechanics and neuromuscular components that Zatsiorsky knows so much about - that you buy the book, or even just hit the library!


I never mentioned the "highest" ones. Of course ME would activate those over RE. (But ME even still will not activate the absolute highest ones.)

You mentioned myofibrillar hypertrophy - most would say that this preferentially induces sarcoplasmic hypertrophy.

What I specifically want to know:

1- According to Zatsiorsky, at what point in the RE method do the HTMUs activate? Last couple reps as failure sets in? Extended sets beyond failure?
2-How could they be activated when fatigue sets in if they weren't activated in the first place? Doesn't this go against the size principle? If the load didn't warrant their activation in the first place, how could they activate at the end of the set (without violating the size principle)?


The more I read about this stuff the more I think Waterbury's principles close to optimal. Work the HTMU's first. Except he seems to think that you recruit all MU's with fast heavy loads, I am still not convinced of that. But I am learning.
Good thread, thanks for the info.


This conflicts with the size principle. The HTMU's are recruited based on the required force, not when the LTMU's get tired and drop out.

If this was true, then the last few reps of a set would be the easiest; because the LTMU's had all dropped out and the HTMU's had started. But since the end of set is where it is the hardest, it is likely that there are not many HTMU's working, and THAT is exactly why it gets more difficult.

So the more force required the more HTMU's are pulled in. That is the size principle.


Oh yeah, very true, I don't know what I was thinking at the time. The only rationalisation I can make is to say that I was watching the Sox game while at work and my full attention wasn't being given to recalling that. Thanks for clarifying that point Lorisco.


Not necessarily. Yes, the HTMU's are capable of producing more force than the intermediate or small MU's on an individual one to one comparison. But, one of the reasons why you can produce so much force during a Max lift or Dynamic lift is because in addition to calling into play the HTMU's you've got the combined force of all of the intermediate and small MU's.

During an RE set, if all of the intermediate and small MU's were already fatigued, then the HTMU's would still have a hard time lifting the load.

Also, I believe that the RE method generally has a minimum load requirement. This usually means that at least some HTMU's are recruited during the beginning of the set.

Now, CW has stated that if the intermediate and small MU's are fatigued that this actually creates a "roadblock" to being able to call the HTMU's into play. If this is true, then it would bring an interesting dimension to the whole RE argument.

It would also make the RE method even more confusing IMO, since it's the single most time tested and statistically effective muscle building technique in history. Yet, if it doesn't even recruit the HTMU's, then one has to ask, "what makes it so damn effective then?"


Based on my experience, the HTMUs get recruited in the last reps of RE. Whenever I do regular standing BB curls, I'm able to do 10 good reps without cheating. Using the same weight with explosive tempo plyometric style, I'm only able to do 7. An 8th rep even with massive cheating was impossible.

I'm thinking that in doing the plyo curls, I exhausted all the HTMUs by the 7th rep. When done normally, the lower threshold fibres fatigue, and on the last reps, the HTMUs take over.


I think this "explosive tempo" is regulated by the CNS. Thus, by forcing a fast bar velocity you are recruiting the HTMUs explicitly over slow and medium STMUs, and the high activation of HTMU fibers yields a comparatively short time to exhaustion.

Anyone else have any thoughts on this?


I don't think the HTMU's come into play all that much during lighter sets done at the "standard" tempo, I.E. not purposely explosive, but just suitable tempo to move the weight. I have been playing with this quite a bit, but of course I am experimenting on myself so it's not like I have a huge research sample. What I have noticed is this. I can take a moderate weight and take it to failure, then quickly pick up a heavier weight and knock out a couple of reps. I wouldn't be able to do that if I had exhausted my HTMU's, this wouldn't be possible. Now I do this as explosively as possible wit every rep, but I cannot seem to tap those HTMU's with out sufficient load. Or rather, they may be tapped, but I cannot exhaust them with the load I am using and hence have something in the tank for a heavier weight.


This is true because the size principle states that smaller MU's are recruited before the bigger MU's. The difference is that while the smaller MU's have less force capability, they have substantially greater endurance. So they get recruited first and then remain after the HTMU's have dropped out.

The smaller MU's don't fatigue that quickly. So they are still there working after the HTMU's have dropped out.


Yes, the smallest MU's do have an incredible resistance to fatigue. But they are also incapable of lifting anything other than an extremely light resistance (like say a pencil). The intermediate fibers on the other hand have much more force potential and can in fact lift decent amounts of resistance. They do have more endurance than the largest fibers, but would still fatigue during the later reps of a moderate rep set.

Also, it's not like all small fibers, all intermediate fibers, and all large fibers are identical in terms of size, endurance, or force capacity. You're going to get a range in each one of those categories. Some FT fibers are going to have just slightly more force capacity and just slightly less fatigue resistance than some intermediate fibers.

In other words while you may not recruit your largest FT fibers during the first reps of a moderate load, moderate rep set to failure, that doesn't mean that you're not going to recruit any FT fibers. And, although your intermediate fibers have more fatigue resistance than your FT fibers, that doesn't mean that you won't fatigue any of them during the duration of the set.

The more fibers you fatigue, the lower your capacity to produce force. Even though you may be calling into play fibers that are on an individual basis capable of producing more force than those which you have fatigued, they still may not be capable of producing more force than the combined efforts of those that have already fatigued.

One other thing to consider is that, during the last couple reps in a set to failure, effort is greatly increased, as is the attempt to move the bar with maximal velocity. Vroom actually brought this point to my attention in a previous thread.

In other words, what is important is not so much the load that is being lifted (although that does play a role), but rather the attempt to produce maximal force. And anyone who has ever done a set to failure will tell you that they are most certainly attempting to produce maximal force during the last couple reps.

This whole concept is pretty much the basis for CW's "maximal recruitment" methodologies. I know that speed seems to be his favorite application of this. But, what is attempting to lift with maximal speed other than one example of attempting to apply maximal force/effort against the bar?

Think about it, if attempting to produce maximal force (speed) works at the beginning of a set, or during a 1RM, then why wouldn't it work at the end of a traditional RE set? Especially since up to that point the largest fibers haven't been working, thus they haven't been fatigued.

Good training,



The issue in fiber recruitment that you seem to be overlooking is that, numerous studies and most all experts agree, the HTMU's have the greatest potential to increase in size and strength. So to a large part, the better you can target the HTMU's the better results you will have.

And that is why CW states that you should try and move the load a fast as possible. Recent studies show that the threshold for HTMU recruitment hits much quicker when you move the load quickly. So that means you have the HTMU working in more reps than if you did the slow steady method.

As for the end of the set, because the load feels very heavy and you try and move it as hard as you can, doesn't mean that it is the HTMU's doing the work. As you said, it is the medium threshold fibers. But these fibers do not have the ability to grow like the HTMU's.

So the entire point is that the slow stead to failure approach works, but not as well because it doesn't involved the HTMU's as much as the speed-focused reps short of failure.


This doesn't square. You can't selectively recruit the HTMUs. If you are utilizing them, the smaller ones are also involved.


This is a fantastic point. In fact, this may be an answer to my question.

Say you're doing RE in the 8-10 rep range. You lift the first 6 reps or so at a moderate, "normal" speed (NOT as fast as possible). Thus, since you are using a load at 80% to 75% of 1RM and lifting at a moderate speed, you are leaving 20-25% of MUs untapped (largest MUs). As failure sets in, you NOW try to lift as fast as possible. Since they were not previously recruited (and therefore NOT fatigued), the HTMUs can NOW be activated since you are attempting to lift as fast as possible.

EDIT: I see that Sentoguy was essentially saying the same thing, as I now just finished reading his post. (When I read the line I cited, I immediately started this post. Next time I'll finish reading first :slight_smile:


Buy Zatsiorsky

learn about ME, RE, and DE, and how all three are good used in combination to get results

learn about Westside and how they have put these together and gotten results that prove they work

or, theorise and try and put together some other incomplete approach

just my thoughts

Zatsiorsky is cheap for what it has in it

Westside has a lot more to it than just another workout routine

Note WS use a modified RE method where they do not go to failure, just a bit short of failure, seems to work fine.

Personally I think that any approach that is neglecting a maximum effort, or not moving with speed, or not going to fatigue, is incomplete.


That would work, but wouldn't you rather activate the HTMU's for all reps instead of just the last few?

The more the HTMU's are activated the greater the potential for growth.