T Nation

Why Aren't The Last Reps Easiest?

In his recent article, “Everything is About to Change”, Chad Waterbury posted the following question:

If the last few reps of a high intensity set really do recruit extra muscle fibers, then why aren’t the last few reps the easiest?

I think that is a very important question to address. I applaud Chad’s efforts, and that of any other lifter or scientist, to further our current level of training knowledge. I am looking forward to Chad fleshing out his theory, and I am envious of his in-depth knowledge of the nervous system. I will do my best to try to answer Chad’s key question and give my rationale for those answers.

Really Chad is asking two points. The first is, do the last reps of a tough set recruit extra motor units (muscle fibers)? The answer is absolutely yes, the last few reps do recruit additional motor units.

I think the easiest way to look at that question is to think about it like this. What percentage of the muscle is left untrained after completing the set? It should be clear that you work a certain percentage of the muscle on the first rep, a larger percentage on the second, and third, etc, so after a tough set you have worked a very large percentage of the overall muscle.

Chad already explained the Size Principle in his article, but in a brief nutshell it says that you will only recruit the motor units necessary to perform the exercise, starting off with the smaller or weaker motor units. As those motor units get tired you then recruit the bigger and stronger motor units.

When you are trying as hard as you can (at the end of the set) you are attempting to recruit the biggest and strongest motor units that you have. There is a very strong correlation between difficulty and the number of motor units recruited. The more difficult something is (or gets) the more motor units over time that have been recruited. You have trained a greater percentage of the muscle with 10 reps than with one rep. You have recruited more motor units to finish a 100 M race than to start one. You have used more motor units in the fourth quarter of a tough game than in the first quarter. This should make common sense.
It is the recruitment of said motor units that contributes to the feeling of exhaustion.

You might ask if we recruit a larger percentage of the muscle as we do more reps and train harder, why don’t we take every set to failure and do 20 sets per exercise? The answer is simply that you would do so much damage that it would be very difficult for you to recover in a reasonable timeframe, and the damage done might not just be micro level damage but might instead be macro level damage, or something serious like a pulled muscle or injured tendon. The goal, which is nothing new, is to do enough to avoid undertraining (too few reps, too few sets) but to prevent overtraining. Of course, walking that fine line is easier said than done.

So if the first part of the question is true, which it definitely is, why then aren’t the last few reps the easiest? This is because some of the motor units that started out working in the set have become fatigued and they are no longer able to contribute effectively to the exercise. So even though a higher percentage of the total motor units are being recruited as the set continues, on a given rep particularly near the end of the set, fewer motor units are able to contribute to that specific rep because the others are fatigued.

Chad used the example of people pushing a car, which I think is a good one. I think about it like this. Let’s say you have 10 people that are available to push a car, so you start off but then it is harder than you thought it would be and some of the people are beginning to get tired. So you get 5 more people to help you push the car and they join in over time. Upon completion of the car push, 15 total people pushed the car (greater than 10) but pushing the car at the end was still hard because most of the people were tired and probably only 2 or 3 strong people were left to push the car.

I have included a chart that I hope will better explain how this phenomenon works. The chart tries to explain motor unit recruitment during a set. The motor units currently in use are in gray, the motor units fatigued are in orange, and the line at the top of the chart represents a person’s theoretical ability to recruit their motor units.

It is curved because I believe there is motor learning taking place during the set, so you can recruit a great number of motor units on rep 2, and 3, and 4 etc until fatigue sets in which limits your ability to recruit the motor units. Hopefully you can see from the chart that as a set progresses, a greater number of motor units are used (a larger percentage of the overall muscle is trained) but each rep gets harder because there are a larger number of fatigued motor units that are not contributing much to the exercise.

Another way to look at it is that each additional rep damages a new part of the muscle that had previously been unused prior to that rep.

Remember that even elite athletes can not recruit 100% of their motor units in most situations. Simply thinking that you want to recruit your motor units does not mean that you will, sometimes you must be forced to do so. Beginners have very poor motor unit recruitment and they must be taught or forced to learn how to recruit their motor units. Normally the toughest motor units to recruit, especially at the beginner or immediate level, are the type II fast twitch motor units, which are the ones that respond best to the training by getting bigger and stronger.

Only the motor units recruited during an exercise are the ones that respond to the exercise, so if you don’t hit that part of the muscle it will not make any significant changes.

I hope that makes some sense. These are important questions and I feel it is important to try to answer them. Given the number of responses to Chad’s article it is obvious that many people are interested in this topic. I am happy to go over anything in this post if desired. Thanks to Chad for writing the article and prompting the discussion, it seems he achieved his purpose of getting people to ask questions.

Tim

Excellent post, Tim! As I was reading CW’s article today at work, I was trying to put this exact same idea into words and was having major difficulties doing so!

Someone did point out in the article discussion that over a large amount of volume, later reps do become easier, as anyone who has used Poliquin’s GVT template knows.

Its an interesting concept, although I think it needs to be fleshed out some more.

Great follow up. CW’s article really seems to be bringing out the best of everyone’s critical thinking abilities on this site.

-dizzle

why aren’t the last reps the easiest???

From my understanding isn’t it due to the size priniciple. we all know that there is an increase in recruitment from smallest/slowest motor units to largest/stronger/faster motor units.
But the largest motor units are also the fastest to drop off. They fatigue quicker than the smaller/slower motor units which fire firstly and therefore more often (everyday activities etc).

This makes the system very common sense. you can’t have the big fast motor units firing first and then fatigueing straight away. you wouldn’t be able to lift much. The slow/small motor units are therefore recruited first because they are more fatigue resistant and therefore can last longer. Then motorunits are added on as they are needed. So at the end the large motorunits fatigue and then drop off and it becomes like the reverse of the size principle. big to small dropping off as you fatigue.

sorry for the long answer
any thoughts???/

There’s still something I don’t get:

Why shouldn’t the fast-twitch fibres get fatigued too, and begin performing poorer and poorer, instead of the body just drops using them?

[quote]Misterhamper wrote:
There’s still something I don’t get:

Why shouldn’t the fast-twitch fibres get fatigued too, and begin performing poorer and poorer, instead of the body just drops using them?[/quote]

Dear Lord, one trainer writes an article and now the world is confused.

Your body is interested in your SURVIVAL. Anyone who studies biology will eventually pick this up after seeing how the body performs in nearly every circumstance.

Therefore, during a set, if your body is interested in keeping you alive and is not aware that this is simply a “training session”, what will help you live better, firing every single fiber off all at once…or releasing the strongest ones first, and then gradually recruiting more fibers as the set progresses and the first to fire get fatigued?

A bodybuilder interested in building the biggest fucking muscle fibers he can wants to get to those fibers latest to fire as well. That is why there are several reps performed over several sets.

Again, I feel more would do better getting some college level biology books rather than worrying about the latest article of the week.

isn’t the whole point about gaining an efficiency in your training. I think this is what the article would be about. people are throwing out different methods of inducing maximum muscle activation without thinking about if it is efficient. laters pk

Wait, so in effect, Westside Barbell methods are the best?

10x3 vs 3x10. 30 total reps either way. A fuckload more speed (or weight) in one system.

This is all too much for my little head right now.

10 people start pushing the car. 6 are marathon runners, 2 are 800m runners and 2 are weighlifters.

They get tired after awhile.

You send in 5 more people. They one day could be strongmen or powerlifters. But at the moment, they are skinny pencil necks who get tired real easy and can’t squat half their bodyweight.

They join in one at a time, and the car keeps moving at the same speed despite the fact that everyone is tired.

After awhile, nobody can push anymore.

There are still another 8 people waiting who never pushed the car, because you are not stupid enough to send all 23 people at once, because they would get trampled.

Now a rhino is coming and you better move that car - all 23 people push, it doesn’t move that fast but you escape the rhino. Nobody knows why the rhino wanted the car.

If you could recruit all your muscle fibers at once you’d rip things - people do that all the time - but even staying way below that level of exertion you do a lot of damage that takes a lot of time to recover from. Whether that is an extra day or week doesn’t matter as long as you recover.

I don’t know why anyone is confused or surprised by any of this.

But the fact that people are means it is an important article to learn ''em good.

[quote]Magarhe wrote:
10 people start pushing the car. 6 are marathon runners, 2 are 800m runners and 2 are weighlifters.

They get tired after awhile.

You send in 5 more people. They one day could be strongmen or powerlifters. But at the moment, they are skinny pencil necks who get tired real easy and can’t squat half their bodyweight.

They join in one at a time, and the car keeps moving at the same speed despite the fact that everyone is tired.

After awhile, nobody can push anymore.

There are still another 8 people waiting who never pushed the car, because you are not stupid enough to send all 23 people at once, because they would get trampled.

Now a rhino is coming and you better move that car - all 23 people push, it doesn’t move that fast but you escape the rhino. Nobody knows why the rhino wanted the car.

If you could recruit all your muscle fibers at once you’d rip things - people do that all the time - but even staying way below that level of exertion you do a lot of damage that takes a lot of time to recover from. Whether that is an extra day or week doesn’t matter as long as you recover.

I don’t know why anyone is confused or surprised by any of this.

But the fact that people are means it is an important article to learn ''em good.[/quote]

so if understand what your saying the last rep is slowest because a car with 23 people in it moves slower than a rhino unless everyone gets out to push.

[quote]Professor X wrote:
Misterhamper wrote:
There’s still something I don’t get:

Why shouldn’t the fast-twitch fibres get fatigued too, and begin performing poorer and poorer, instead of the body just drops using them?

Dear Lord, one trainer writes an article and now the world is confused.

Your body is interested in your SURVIVAL. Anyone who studies biology will eventually pick this up after seeing how the body performs in nearly every circumstance.

Therefore, during a set, if your body is interested in keeping you alive and is not aware that this is simply a “training session”, what will help you live better, firing every single fiber off all at once…or releasing the strongest ones first, and then gradually recruiting more fibers as the set progresses and the first to fire get fatigued?

A bodybuilder interested in building the biggest fucking muscle fibers he can wants to get to those fibers latest to fire as well. That is why there are several reps performed over several sets.

Again, I feel more would do better getting some college level biology books rather than worrying about the latest article of the week.[/quote]

good point

[quote]wukey wrote:
so if I understand what your saying the last rep is slowest because a car with 23 people in it moves slower than a rhino unless everyone gets out to push.[/quote]

Guess the fast-twitch people fucked up!

This had been mentioned before but…

How on earth is your training “wrong” or fatally flawed if one, you get satisfactory resluts from it and actually enjoy it?

Wasn’t it scientifically proven years ago that the bumblebee cannot possible fly due to it’s many flaws in aerodynamics and power-to-weight ratio etc?

Just don’t tell that to the bumblebee!

EDIT: RESULTS not RESLUTS (although I have nothing against sluts)

Sorry, Tim, but your understanding of the size principle is wrong. Go back and read CW’s explanation again. Or as Prof X suggested, go get yourself a college level exercise physiology or biology text book.

The size principle is based on required amounts of force, not on number of repetitions in a set or fatigue. Basically the smallest motor units are recruited first. These motor units are the most fatigue resistant but also have the least force producing potential. Think in terms of just every day hand gestures or picking up a pencil.

As more force is required the body recruits motor units with higher and higher force producing potential, but which are much less resistant to fatigue.

For instance, if you try to pick up a weight that is nearing the amount of weight that you can only pick up once your body will first recruit the smallest motor units, however they won’t be able to perform the task. So, it’ll recruit bigger and bigger motor units until either you lift the weight or give up because you are incapable of lifting the weight.

This has nothing to do with reps in a set or fatigue. The same goes for speed. The greater the acceleration of the mass, the greater the force, thus the greater the motor unit recruitment.

CW’s point in asking the question, “if the last few reps in a high intensity set really do recruit extra muscle fibers, then why aren’t the last few reps the easiest?” is that he is trying to show that you DON’T recruit more muscle fibers during the last few reps of a high intensity set.

That’s actually a question that I’ve posed before on this site in regards to ways to recruit all of your voluntary muscle fibers, I came to the same conclusion that CW seems to have.

What CW is saying is that if you are lifting a high enough percentage of 1RM (anything 85% or greater), or moving the weight with maximum speed, then due to the size principle you are already recruiting every possible motor unit/muscle fiber on the very first rep of the set.

The reason that the reps get more difficult as the set goes on is due to several factors.

  1. Since the type 2b/FF muscle fibers/motor units are the quickest to fatigue, the smaller less powerful muscle fibers are now less easily able to move the weight (or move it as quickly). This is how/why drop sets work.

  2. Hydrogen ion build up. After approximately 10 seconds your body switches from your ATP-CP system to Glycolysis which produces lactic acid as a by product. Now, some of this lactic acid is buffered thus producing lactate which can then be used as more fuel. However, there are also hydrogen atoms that build up in the muscle and cause interference between actin and myosin crossbridges, thus inhibiting contraction. This hydrogen ion build up is responsible for the “burn” that you feel during exercise.

The point is that if the last few reps really did recruit larger more powerful muscle fibers, then those reps would be easier. In fact, if your understanding of the size principle was correct, then you would never reach failure because the more reps/fatigue encountered in a set the stronger you would get. Therefore, he is suggesting that this line of thinking is incorrect.

Also, unfortunately your graph is also incorrect. The bars should be up near the “Theoretical Maximal Recruitment” line right from rep #1. And, the orange should start from the top down, not the bottom up. The smallest most fatigue resistant fibers/MU’s that are always recruited during any physical movement are ridiculously fatigue resistant. They can literally go on for days. Just think, can you walk for longer, or run for longer. Why? After all you are using the same muscles?

Hope this helps to clear things up.

Good training,

Sentoguy

Sentoguy,

That was the most lucid, concise post I’ve seen on this whole topic of motor unit recruitment. Nice work.

[quote]derek wrote:

EDIT: RESULTS not RESLUTS (although I have nothing against sluts)[/quote]

OR reusing them.

-dizzle

[quote]Sentoguy wrote:
Sorry, Tim, but your understanding of the size principle is wrong. Go back and read CW’s explanation again. Or as Prof X suggested, go get yourself a college level exercise physiology or biology text book.

The size principle is based on required amounts of force, not on number of repetitions in a set or fatigue. Basically the smallest motor units are recruited first. These motor units are the most fatigue resistant but also have the least force producing potential. Think in terms of just every day hand gestures or picking up a pencil.

As more force is required the body recruits motor units with higher and higher force producing potential, but which are much less resistant to fatigue.

For instance, if you try to pick up a weight that is nearing the amount of weight that you can only pick up once your body will first recruit the smallest motor units, however they won’t be able to perform the task. So, it’ll recruit bigger and bigger motor units until either you lift the weight or give up because you are incapable of lifting the weight.

This has nothing to do with reps in a set or fatigue. The same goes for speed. The greater the acceleration of the mass, the greater the force, thus the greater the motor unit recruitment.

CW’s point in asking the question, “if the last few reps in a high intensity set really do recruit extra muscle fibers, then why aren’t the last few reps the easiest?” is that he is trying to show that you DON’T recruit more muscle fibers during the last few reps of a high intensity set.

That’s actually a question that I’ve posed before on this site in regards to ways to recruit all of your voluntary muscle fibers, I came to the same conclusion that CW seems to have.

What CW is saying is that if you are lifting a high enough percentage of 1RM (anything 85% or greater), or moving the weight with maximum speed, then due to the size principle you are already recruiting every possible motor unit/muscle fiber on the very first rep of the set.

The reason that the reps get more difficult as the set goes on is due to several factors.

  1. Since the type 2b/FF muscle fibers/motor units are the quickest to fatigue, the smaller less powerful muscle fibers are now less easily able to move the weight (or move it as quickly). This is how/why drop sets work.

  2. Hydrogen ion build up. After approximately 10 seconds your body switches from your ATP-CP system to Glycolysis which produces lactic acid as a by product. Now, some of this lactic acid is buffered thus producing lactate which can then be used as more fuel. However, there are also hydrogen atoms that build up in the muscle and cause interference between actin and myosin crossbridges, thus inhibiting contraction. This hydrogen ion build up is responsible for the “burn” that you feel during exercise.

The point is that if the last few reps really did recruit larger more powerful muscle fibers, then those reps would be easier. In fact, if your understanding of the size principle was correct, then you would never reach failure because the more reps/fatigue encountered in a set the stronger you would get. Therefore, he is suggesting that this line of thinking is incorrect.

Also, unfortunately your graph is also incorrect. The bars should be up near the “Theoretical Maximal Recruitment” line right from rep #1. And, the orange should start from the top down, not the bottom up. The smallest most fatigue resistant fibers/MU’s that are always recruited during any physical movement are ridiculously fatigue resistant. They can literally go on for days. Just think, can you walk for longer, or run for longer. Why? After all you are using the same muscles?

Hope this helps to clear things up.

Good training,

Sentoguy[/quote]

While I like the way you laid that out, I disagree that any reps past the point where the set gets harder simply don’t recruit any more fibers or that it has no use in building more size. If this were the case, the guys barely breaking a sweat would be growing faster than anyone.

Any serious lifter here should know you aren’t just training your muscles when you lift but also your perception of what “heavy” even is and how your body/mind adapts to stress. This isn’t simply about the muscle tissue alone. The human mind (read as mind/muscle connection if you like) can be the X-factor and leaving that out just to make a new program that sounds really neat and concise would be a mistake.

This is why most people who simply worry about what “should” work are usually so much smaller than those who also pay attention to what IS working and HAS worked for decades.

[quote]Professor X wrote:

While I like the way you laid that out, I disagree that any reps past the point where the set gets harder simply don’t recruit any more fibers or that it has no use in building more size. If this were the case, the guys barely breaking a sweat would be growing faster than anyone.

Any serious lifter here should know you aren’t just training your muscles when you lift but also your perception of what “heavy” even is and how your body/mind adapts to stress. This isn’t simply about the muscle tissue alone. The human mind (read as mind/muscle connection if you like) can be the X-factor and leaving that out just to make a new program that sounds really neat and concise would be a mistake.

This is why most people who simply worry about what “should” work are usually so much smaller than those who also pay attention to what IS working and HAS worked for decades.[/quote]

Hey X,

Nor was I trying to suggest that lifting past the point where the weight starts to get heavy was worthless for building muscle.

I was simply trying to clear up the incorrect interpretation of the size principle that started this thread.

I agree with you that there are definitely benefits to pushing yourself and approaching or even reaching momentary muscular failure. For instance, hormonal factors. I mentioned lactic acid, which is a stimulus for GH release.

I also completely agree about the mental aspects of pushing yourself during lifting. Heavy is most certainly as much mental as it is physical in a lot of cases.

I also was not suggesting that someone should stop once the set starts to get difficult, nor am I completely sold on CW’s new article. Like you stated in one of your posts in the discussion of that article, I like some of the concepts and have have used several of them in my training in the past. I am not going to just forget everything else that I’ve ever read, seen, been told, or experienced simply because someone comes a long and tells me that they’ve got the “most revolutionary workout ever” (which by the way isn’t exactly what CW said, but it’s along those lines).

I tend to research a lot and if a new training concept or methodology comes along that makes sense to me, I’ll try it, or at least take elements from it and work them into what I’m already doing. If it works, great. If not, oh well, then I won’t use it any more or use it with any of the people that I train.

I agree with you though that a lot of people seem to over analyze things and as a result don’t ever stick to a program long enough to see results. Like you said, there are methods already existing that have worked for countless athletes/bodybuilders. We shouldn’t just disregard them. Results are what we’re all after, and results are really the only litmus test to how effective a training program is.

Good training,

Sentoguy

[quote]Professor X wrote:
I disagree that any reps past the point where the set gets harder simply don’t recruit any more fibers or that it has no use in building more size. If this were the case, the guys barely breaking a sweat would be growing faster than anyone.[/quote]

That’s an overstatement, obviously nobody advocates training like someone going through the motions. As for last reps, I know the nerves are getting stressed but probably not more fibers. Especially since it’s a fact that more units recruited allows for lifting faster not slower.

I never tried paying attention to speed decline but I do know that if you stop right at the point where it ‘gets heavy’ you can do a lot more sets with any weight then just repping out.

One thing I dont understand about this whole thing is that it cant help us build muscle faster than is physiologically possible.

And if it is such a breakthrough, why are so many people already getting big and strong using the “old school” methods.