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Fiber Recruitment
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bronx

Massachusetts, USA

Question about fiber recruitment.Does the first rep of lets say 10 rep failure include only slow to fatigue then progressively increase more slow to fatigue then hit fast to fatigue as you reach failure,or does it only fatigue the amount of fibers call upon.
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Nwlifter

bronx wrote:
Question about fiber recruitment.Does the first rep of lets say 10 rep failure include only slow to fatigue then progressively increase more slow to fatigue then hit fast to fatigue as you reach failure,or does it only fatigue the amount of fibers call upon.


10RM will recruit almost all your fibers, the ones that aren't recruited, will be recruited in the next few reps as fatigue builds. By the time you hit failure with your 10RM, all your fibers are not only recruited, but have hit maximum rate coding (firing frequency) and even started dropping back out from high fatigue.

Ron

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bill1

California, USA

I think it depends in a large part on your own unique individual fiber type composition to some extant. But if I have it right , the order goes from slow to fast. That is the slow fibers fire first and then, as required to continue the work ,the next fastest fibers fire and so on. This is one of the reasons why I think it is neccessary to work to momentary muscular failure. If you don't you will not recruit and thus work the really fast fibers. And it is the fast fibers that have the most potential for hypertrophy.

Bill
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Nwlifter

I'll post this again, it's verified 'true' info.

(at most, it takes 85% effort to fully recruit all fibers)

"The relative contribution of motor unit recruitment to muscle force varies between muscles. In some hand muscles for example, all motor units are recruited at around 50% of maximum. In other muscles, such as the bicep brachii, deltoid, and tiblias anterior, motor unit recuitment continues upto 85% of the maximum force (Deluca, LeFever, McCue & Xenakis, 1982a; Kukulka & Clamann, 1981; Van Cutsem et al,. 1997)"
From p290, Neuromechanics of Human Movement 3rd Edition. Roger M. Enoka
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bill1

California, USA

Nwlifter wrote:
I'll post this again, it's verified 'true' info.

(at most, it takes 85% effort to fully recruit all fibers)

"The relative contribution of motor unit recruitment to muscle force varies between muscles. In some hand muscles for example, all motor units are recruited at around 50% of maximum. In other muscles, such as the bicep brachii, deltoid, and tiblias anterior, motor unit recuitment continues upto 85% of the maximum force (Deluca, LeFever, McCue & Xenakis, 1982a; Kukulka & Clamann, 1981; Van Cutsem et al,. 1997)"
From p290, Neuromechanics of Human Movement 3rd Edition. Roger M. Enoka


Do you have a link for this?

Bill
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Nwlifter

bill1 wrote:
Nwlifter wrote:
I'll post this again, it's verified 'true' info.

(at most, it takes 85% effort to fully recruit all fibers)

"The relative contribution of motor unit recruitment to muscle force varies between muscles. In some hand muscles for example, all motor units are recruited at around 50% of maximum. In other muscles, such as the bicep brachii, deltoid, and tiblias anterior, motor unit recuitment continues upto 85% of the maximum force (Deluca, LeFever, McCue & Xenakis, 1982a; Kukulka & Clamann, 1981; Van Cutsem et al,. 1997)"
From p290, Neuromechanics of Human Movement 3rd Edition. Roger M. Enoka

Do you have a link for this?

Bill


That I typed from a book "Neuromechanics of Human Movement". The studies he references, amoung others can be found though.

Also,
"Keio J Med. 1994 Sep;43(3):137-42. Related Articles, Links


Motor unit firing behavior in man.

Masakado Y.


Studies on motor unit firing behavior in man by the decomposition technique are described. The decomposition technique identifies motor unit firing with 100% accuracy at force levels of greater than 80% maximal voluntary contraction (MVC). In all muscles examined, the higher the recruitment threshold of the motor unit, the lower the rate at which it fired at the target level. Smaller muscles, such as those in the hand, recruit their motor units at 0-50% MVC and rely exclusively on firing rate increases to augment force output at 50-100% MVC. Larger muscles, such as those in the leg or arm, recruit motor units at least to 90% MCV, and possibly higher. Their firing rates have a relatively smaller dynamic swing. Thus, smaller muscles rely primarily on firing rate and larger muscles rely primarily on recruitment to modulate their force. High cross-correlation functions in firing rate behavior within a muscle were observed between individual motor unit firing rates at constant force isometric contraction. Thus the nervous system does not control the firing rate of motor units individually. Instead, it acts on the pool of homonymous motoneurons in a uniform fashion. Electrical stimulation of cutaneous receptors tends to increase the recruitment thresholds of low-threshold motor units and to decrease their firing rates, while high-threshold motor units generally exhibit a decrease in recruitment threshold and an increase in firing rate."

"eu et al. (2000) in (p.376) write:
"a majority of studies using the TI technique have concluded that
healthy subjects, regardless of their age, gender, or physical
condition, can fully activate most of the limb muscles."

Behm (1995) (p. 265) in another review writes "The TI was first used by Merton, who described full activation of the adductor pollicis muscle with fatigue. Full activation of the tibialis anterior (Bellanger and McComas, 1981) , elbow flexors , abductor digiti minimi (Gandevia and McKenzie, 1988) quadriceps (Chapman et al., 1985; Rice et al., 1992), adductor pollicis, and soleus (Bellemare et al., 1983) have been reported in untrained individuals.

Sale (1987) in another review in (p.121) writes:
"in the majority of studies, subjects were able to produce voluntary contractions equal in force to contractions evoked by tetanic stimulation."

"Electromyographic and mechanomyographic estimation of motor unit activation strategy in voluntary force production.

Akataki K, Mita K, Watakabe M.

Department of Functioning Science, Institute for Developmental Research, Aichi Human Service Center, Kasugai 480-0392, Japan. akataki@inst-hsc.jp

Electromyographic and mechanomyographic estimation of motor unit activation strategy in voluntary force production. In order to determine whether electromyogram (EMG) and mechanomyogram (MMG) are suitable for the noninvasive estimation of the motor unit (MU) activation strategy, the EMG/force and MMG/force relationships were examined simultaneously during isometric ramp contractions in biceps brachii muscle. The highest mean power frequency (MPF) of the EMG, which reflects the full MU recruitment, was determined at 51% MVC. Two obvious inflection points were identified on the MMG-amplitude/force relationship that showed an initial slow increase followed by a rapid increase and a progressive decrease at higher force levels. Our results suggest that the MMG amplitude allows the estimation of the beginning of recruitment of MUs that innervate the first-twitch fibers in addition to identification of the full MU recruitment. The rate coding strategy was qualitatively reflected by the MMG-MPF/force relationship. We conclude that the MU activation strategy is estimated in more detail by the MMG than by the EMG."

Also, in Komi's "Strength and Power in Sport" he verifies this.

I have a couple pages of Neuromechanics scanned in but we need to be emailed.

Cheers,
Ron

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bill1

California, USA

Thanks Ron, very interesting stuff!

Bill
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glenn_001

New Zealand

bill1 wrote:
I think it depends in a large part on your own unique individual fiber type composition to some extant. But if I have it right , the order goes from slow to fast. That is the slow fibers fire first and then, as required to continue the work ,the next fastest fibers fire and so on. This is one of the reasons why I think it is neccessary to work to momentary muscular failure. If you don't you will not recruit and thus work the really fast fibers. And it is the fast fibers that have the most potential for hypertrophy.

Bill


Is this why doing 8-12 reps instead of 1-3 is better? gets all the fibres to fire?

Glenn

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bill1

California, USA

glenn_001 wrote:
bill1 wrote:
I think it depends in a large part on your own unique individual fiber type composition to some extant. But if I have it right , the order goes from slow to fast. That is the slow fibers fire first and then, as required to continue the work ,the next fastest fibers fire and so on. This is one of the reasons why I think it is neccessary to work to momentary muscular failure. If you don't you will not recruit and thus work the really fast fibers. And it is the fast fibers that have the most potential for hypertrophy.

Bill

Is this why doing 8-12 reps instead of 1-3 is better? gets all the fibres to fire?

Glenn



Yes, if you have the usual " mix " of fast and slow fibers. However if you have a predominance of fast twitch fibers they will be recruited very quickly, perhaps within the first few reps, and for such an individual only a very few reps may be needed.
And more or less visa versa for slow twitch predominance.

Bill
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Nwlifter

Thanks Ron, very interesting stuff!

Bill


Your welcome :)



Is this why doing 8-12 reps instead of 1-3 is better? gets all the fibres to fire?

Glenn



3RM will surely fire all your fibers, even during the first rep. In fact, 6-8RM will cause all your fibers to fire during the first rep and from then on. I think the problem with using too low of reps or low TUL, is just because a fiber 'fires' doesn't mean it was worked enough to be stimulated.

You can do a 1 second all out isometric bench, and all your fibers will 'fire' for that one second but we know that isn't optimal for hypertrophy.

Ron

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bill1

California, USA

Nwlifter wrote:
" Thus, smaller muscles rely primarily on firing rate and larger muscles rely primarily on recruitment to modulate their force.


Did everybody catch this?

Bill
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Sesame

bill1 wrote:
Nwlifter wrote:
" Thus, smaller muscles rely primarily on firing rate and larger muscles rely primarily on recruitment to modulate their force.

Did everybody catch this?

Bill


I caught it, so what? I'll work my finger adductors with a longer TUL! LOL
Seriously, so what?
:)

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simon-hecubus

Texas, USA

Sesame wrote:
bill1 wrote:
I caught it, so what? I'll work my finger adductors with a longer TUL! LOL
Seriously, so what?
:)



I guess if you work your hands for an all-out 3-minute set, you only get see one of the lesser gods. ;-)

Scott
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simon-hecubus

Texas, USA

Sorry, but I couldn't help myself on that one.

Seriously though, very interesting thread, guys. I guess if I'm ever asked, I'll have to try and condense this info into a concise response.

Scott
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bill1

California, USA

Sesame wrote:
bill1 wrote:
Nwlifter wrote:
" Thus, smaller muscles rely primarily on firing rate and larger muscles rely primarily on recruitment to modulate their force.

Did everybody catch this?

Bill

I caught it, so what? I'll work my finger adductors with a longer TUL! LOL
Seriously, so what?
:)



I wanted to point it out ,as I got the impression that the concept of hierarchical recruitment was being challenged, and this statement obviously supports it. Thats all.

Bill
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spartakos

Ontario, CAN

Thanks to everyone who contributed to this thread and especially to Ron for posting those studies.

I hope I don't come across as too dumb by asking how we can apply the info on muscle recruitment in the gym.

Do the results of the studies suggest that we do sets to 85% of maximum failure? I'm confused.
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Nwlifter

Your very welcome :)

Orderly Recruitment: All muscles rely on this, large or small, it's just the larger muscles tend to reach full recruitment at much higher effort levels. 85% or so.
Smaller muscles reach full recruitment at lower effort levels, 40-50% on average.

Practical use: The main 'good thing' to know about this, is that you do not have to worry if you 'used all your fibers' during a workout. If you reached 85% or more of maximum effort, (whether it be the first rep with 85% of 1RM or the 12th rep of a lighter set), you have indeed contracted all your fibers. Whether you used them enough for proper stimulation is another subject, BUT, you did recruit all your fibers.

Cheers,
Ron
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tylerg

Nwlifter wrote:
Your very welcome :)

Orderly Recruitment: All muscles rely on this, large or small, it's just the larger muscles tend to reach full recruitment at much higher effort levels. 85% or so.

Smaller muscles reach full recruitment at lower effort levels, 40-50% on average.


Cheers,
Ron


I hear what you are saying. It was my belief that the slower fatiguing, smaller muscles were recruited first. After a few reps, the intermediate twitch muscles were recruited then towards the end of the set, the fast twitch muscles were utilized.

Based on your last paragraph (which I deleted for expediency) are you saying there is no need to go through the process of reps if the first rep is at 85%? If training to failure, shouldn't we be 80% to begin with? In which case, the second rep would be utilizing all the fibers. I could be way off here as I have just finished over a week of graveyards...mind is mud:)

Comments

Tyler



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NeuroMass

According the the the LAW of MUSCLE FIBER RECRUITMENT the first ones to be recruited are the red slow twitch fibers then that intermediate fibers and as you start nearing maximum effort and your muscles grows more fatigue your body will start recruiting the white fast twitch fibers.

Of course when you lift weights especially heavier weights wherein you fail sooner (say 6 reps) youwill be recruiting a combination of muscle fibers staring from your first rep because of GREATER force requirement.

PEACE.
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Nwlifter

tylerg wrote:

I hear what you are saying. It was my belief that the slower fatiguing, smaller muscles were recruited first. After a few reps, the intermediate twitch muscles were recruited then towards the end of the set, the fast twitch muscles were utilized.

Based on your last paragraph (which I deleted for expediency) are you saying there is no need to go through the process of reps if the first rep is at 85%? If training to failure, shouldn't we be 80% to begin with? In which case, the second rep would be utilizing all the fibers. I could be way off here as I have just finished over a week of graveyards...mind is mud:)

Comments

Tyler





Like Neuro said, yes we have orderly recruitment, and force dictates how many fibers are recruited. Specifically, percentage of effort. Effort is generated in the CNS and the effort you feel is basically your neural activation.

OK, now I'll try to make this more simple, I have a tendancy to focus on one thing and maybe are leaving you confused...

Let's say you have an isometric curl machine with a spring scale attached. You grab the bar and curl absolutely as hard as you can. It reads 125 lbs on the scale. This is your MVC, your maximum voluntary contraction. Now, if you curl again but with 85% of that force, which is 106.25 lbs, this is enough effort to recruit all the fibers in your biceps. If you increase your force from that 106.25 to the max of 125, you gain the extra force by rate coding. This is your fibers twitching at a faster rate.

Now, this also applies with lesser weights. Let's say you use that same curl machine but only curl with 80lbs of force. Now the effort is low enough that all fibers are not firing, BUT, if you continue the contraction, as fatigue builds, the fibers that ARE firing are becoming weaker, so to maintain that 80lbs of force, more fibers are recruited. When you fatigue enough that your strength is now down to 94lbs for a full effort, that 80lbs is now 85% of your fatigued max so by that time, all fibers are recruited. If you continue the contraction, rate coding will increase until your so fatigued you cannot maintain even the 80lbs of force.

starting weight: Yes, if you start with 85% or more of your 1RM, during the parts of the exercise (the hard part of the ROM) all your fibers will be firing even during the first rep. But we still need to do more than one rep as...

1) Just contracting a fiber isn't enough TUL for hypertrophy, it needs to be worked for some minimum TUL.

2) Because of the changes in angles on the exercise, some parts are easier so during a full range exercise, recruitment increases and decreases as the leverages change.

Hope that explains it better :)

Ron

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bill1

California, USA

Nwlifter wrote:
tylerg wrote:

I hear what you are saying. It was my belief that the slower fatiguing, smaller muscles were recruited first. After a few reps, the intermediate twitch muscles were recruited then towards the end of the set, the fast twitch muscles were utilized.

Based on your last paragraph (which I deleted for expediency) are you saying there is no need to go through the process of reps if the first rep is at 85%? If training to failure, shouldn't we be 80% to begin with? In which case, the second rep would be utilizing all the fibers. I could be way off here as I have just finished over a week of graveyards...mind is mud:)

Comments

Tyler





Like Neuro said, yes we have orderly recruitment, and force dictates how many fibers are recruited. Specifically, percentage of effort. Effort is generated in the CNS and the effort you feel is basically your neural activation.

OK, now I'll try to make this more simple, I have a tendancy to focus on one thing and maybe are leaving you confused...

Let's say you have an isometric curl machine with a spring scale attached. You grab the bar and curl absolutely as hard as you can. It reads 125 lbs on the scale. This is your MVC, your maximum voluntary contraction. Now, if you curl again but with 85% of that force, which is 106.25 lbs, this is enough effort to recruit all the fibers in your biceps. If you increase your force from that 106.25 to the max of 125, you gain the extra force by rate coding. This is your fibers twitching at a faster rate.

Now, this also applies with lesser weights. Let's say you use that same curl machine but only curl with 80lbs of force. Now the effort is low enough that all fibers are not firing, BUT, if you continue the contraction, as fatigue builds, the fibers that ARE firing are becoming weaker, so to maintain that 80lbs of force, more fibers are recruited. When you fatigue enough that your strength is now down to 94lbs for a full effort, that 80lbs is now 85% of your fatigued max so by that time, all fibers are recruited. If you continue the contraction, rate coding will increase until your so fatigued you cannot maintain even the 80lbs of force.

starting weight: Yes, if you start with 85% or more of your 1RM, during the parts of the exercise (the hard part of the ROM) all your fibers will be firing even during the first rep. But we still need to do more than one rep as...

1) Just contracting a fiber isn't enough TUL for hypertrophy, it needs to be worked for some minimum TUL.

2) Because of the changes in angles on the exercise, some parts are easier so during a full range exercise, recruitment increases and decreases as the leverages change.

Hope that explains it better :)

Ron



GREAT!

Bill
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Sesame

Nwlifter wrote:
tylerg wrote:

I hear what you are saying. It was my belief that the slower fatiguing, smaller muscles were recruited first. After a few reps, the intermediate twitch muscles were recruited then towards the end of the set, the fast twitch muscles were utilized.

Based on your last paragraph (which I deleted for expediency) are you saying there is no need to go through the process of reps if the first rep is at 85%? If training to failure, shouldn't we be 80% to begin with? In which case, the second rep would be utilizing all the fibers. I could be way off here as I have just finished over a week of graveyards...mind is mud:)

Comments

Tyler





Like Neuro said, yes we have orderly recruitment, and force dictates how many fibers are recruited. Specifically, percentage of effort. Effort is generated in the CNS and the effort you feel is basically your neural activation.

OK, now I'll try to make this more simple, I have a tendancy to focus on one thing and maybe are leaving you confused...

Let's say you have an isometric curl machine with a spring scale attached. You grab the bar and curl absolutely as hard as you can. It reads 125 lbs on the scale. This is your MVC, your maximum voluntary contraction. Now, if you curl again but with 85% of that force, which is 106.25 lbs, this is enough effort to recruit all the fibers in your biceps. If you increase your force from that 106.25 to the max of 125, you gain the extra force by rate coding. This is your fibers twitching at a faster rate.

Now, this also applies with lesser weights. Let's say you use that same curl machine but only curl with 80lbs of force. Now the effort is low enough that all fibers are not firing, BUT, if you continue the contraction, as fatigue builds, the fibers that ARE firing are becoming weaker, so to maintain that 80lbs of force, more fibers are recruited. When you fatigue enough that your strength is now down to 94lbs for a full effort, that 80lbs is now 85% of your fatigued max so by that time, all fibers are recruited. If you continue the contraction, rate coding will increase until your so fatigued you cannot maintain even the 80lbs of force.

starting weight: Yes, if you start with 85% or more of your 1RM, during the parts of the exercise (the hard part of the ROM) all your fibers will be firing even during the first rep. But we still need to do more than one rep as...

1) Just contracting a fiber isn't enough TUL for hypertrophy, it needs to be worked for some minimum TUL.

2) Because of the changes in angles on the exercise, some parts are easier so during a full range exercise, recruitment increases and decreases as the leverages change.

Hope that explains it better :)

Ron




This is a good general explanation of how things probably unfold during a set under these conditions, however..

1) "all fibers recruited @85% MVC" -i, personally, know of only ONE study (actually, wasn't even the full study only the abstract) posted here to support this claim, so I am treating this as an working assumption at this point.

2)"Because of the changes in angles on the exercise, some parts are easier so during a full range exercise, recruitment increases and decreases as the leverages change." -this is an assumption and it seems reasonable enough but to my knowledge hasn't been verified yet, has it?

3)"Just contracting a fiber isn't enough TUL for hypertrophy, it needs to be worked for some minimum TUL." -i wonder why?
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Nwlifter

This is a good general explanation of how things probably unfold during a set under these conditions, however..

1) "all fibers recruited @85% MVC" -i, personally, know of only ONE study (actually, wasn't even the full study only the abstract) posted here to support this claim, so I am treating this as an working assumption at this point.


I've posted 2 abstracts on this, plus Komi speaks of this in his book "Strength and Power in Sport", along with references, as does Roger M. Enoka in Neuromechanics of Human Movement, also with references.

"The relative contribution of motor unit recruitment to muscle force varies between muscles. In some hand muscles for example, all motor units are recruited at around 50% of maximum. In other muscles, such as the bicep brachii, deltoid, and tiblias anterior, motor unit recuitment continues upto 85% of the maximum force (Deluca, LeFever, McCue & Xenakis, 1982a; Kukulka & Clamann, 1981; Van Cutsem et al,. 1997)"
From p290, Neuromechanics of Human Movement 3rd Edition. Roger M. Enoka


2)"Because of the changes in angles on the exercise, some parts are easier so during a full range exercise, recruitment increases and decreases as the leverages change." -this is an assumption and it seems reasonable enough but to my knowledge hasn't been verified yet, has it?


Most definately. Not only are there studies, but just knowing that recruitment is orderly by force (which there are uncountable studies on)and knowing some simple physics, (that leverage factors do change during exercise, which is easy to see and feel) you can extrapolate that force requirements change also. This means, if force falls below 85% of MVC, then recruitment will also drop.


3)"Just contracting a fiber isn't enough TUL for hypertrophy, it needs to be worked for some minimum TUL." -i wonder why?


Just recruiting a fiber does not cause any of these factors related to hypertrophy.
*ATP exhaustion
*Calcium influx
*Micro-tears
*Satellite cell activation.
*ect.

Cheers,
Ron
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