Determining if you're fast twitch?

[PowerManDL]

@jman316

PowermanDL, I have read many sources as of late that approximate what you stated in your post.

Noting that the training stimulus yields fiber type conversion. I feel that it must also be noted that although, for instance, a type I fiber may assume the characteristics of a type II fiber (by way of specific training) the type II fibers also respond to the specific training parameters and therefore develop greater force production values than the type I counterparts.

So I hypothesize that if a type I dominant individual and a type II dominant individual, both who are untrained and possess equal biomechanics, tendon insertions, etc., are simultaneously introduced to a short sprint training protocol, the type II dominant individual will continually out perform the type I dominant individual in the short sprints because of a greater response to the training stimulus.

Do you agree?

James

I do agree, if such conditions actually exist. I’m not certain that they do, at least not to a degree that would impact performance significantly on their own. I’d be much more concerned with hormonal, autocrine/paracrine, and histo-immune factors, since these are going to determine how much training the individual can perform and recover from in a reasonable time frame. When considering performance, anatomical structure aside, the nervous system is only one part of the game.

However, even in that case, I want to add the caveat that it isn’t the particular MHC isoform being expressed that is “at fault” for the change in performance. It’s the neural “wiring” for the FT/ST ratio. MHC expression doesn’t affect performance-- the shift from so-called “fast” to “slow” isoforms is the observed shift from IIx -> IIa. MHC IIx doesn’t do anything in humans, apparently. It’s a marker of disuse and of detraining. That suggests that it isn’t very appropriate for strength or speed, on its own merit, let alone the continuing research showing that it is indeed neural output that is responsible for functional characteristics. The fiber types only follow the function of the fiber.

When you bear in mind that the only real difference between IIx and IIa is the shortening velocity, not force production, it makes sense. IIx is thought to contract “too fast” to be of any use in strength training activity, and this fits observation. Additionally, I’m not aware of any reasons why any program using weights ~60% or higher, following all the usual protocols (fast, heavy, whatever) would result in a shift to MHC-I. That just doesn’t happen; type I expresses under heavy aerobic conditions, as a way of making the fiber more efficient, not during any strength activities.

[martn76]

@PowerManDL

I do agree, if such conditions actually exist. I’m not certain that they do, at least not to a degree that would impact performance significantly on their own. I’d be much more concerned with hormonal, autocrine/paracrine, and histo-immune factors, since these are going to determine how much training the individual can perform and recover from in a reasonable time frame. When considering performance, anatomical structure aside, the nervous system is only one part of the game.

However, even in that case, I want to add the caveat that it isn’t the particular MHC isoform being expressed that is “at fault” for the change in performance. It’s the neural “wiring” for the FT/ST ratio. MHC expression doesn’t affect performance-- the shift from so-called “fast” to “slow” isoforms is the observed shift from IIx -> IIa. MHC IIx doesn’t do anything in humans, apparently. It’s a marker of disuse and of detraining. That suggests that it isn’t very appropriate for strength or speed, on its own merit, let alone the continuing research showing that it is indeed neural output that is responsible for functional characteristics. The fiber types only follow the function of the fiber.

When you bear in mind that the only real difference between IIx and IIa is the shortening velocity, not force production, it makes sense. IIx is thought to contract “too fast” to be of any use in strength training activity, and this fits observation. Additionally, I’m not aware of any reasons why any program using weights ~60% or higher, following all the usual protocols (fast, heavy, whatever) would result in a shift to MHC-I. That just doesn’t happen; type I expresses under heavy aerobic conditions, as a way of making the fiber more efficient, not during any strength activities.

People seem to suggest that type II fibres can not become slow or express slow MHC. Prolonged strength training akin to bodybuilding WILL lead to type IIa becoming type IIc. This unwanted hybrid will express a fast IIa MHC bound to type Ic MHC. The innervation of the muscle (determined by the CNS) WILL become slow. Prolonged bodybuilding methods without periods of rest and switching of strength training methods will cause this. The muscle fibre will slow in its ability to relax, this may even lead to slower sprint times. Type IIx ARE useful, the reason they transform leftwards to type IIa is due to thermodynamic efficiency. Basically type IIx/b can not “turnover” phospates and sugar fast enough because they lack the ability to utilise oxygen to turn by products back to phosphate and glucose.

Speed training on the other hand leads to slow to fast type IIa MHC conversion being and fast type IIx MHC expressing type IIa MHC. In other words an increase in type IIa occurs where as in strength training an increase of type IIc occurs. Whether you want to believe this or not these are the disconcerting findings of numerous papers I have come across. Yes the CNS is king but it loves efficiency and efficieny means slower innervation frquencies, an affinity to slower MHCs and light chains.

The point I am trying to make is that too much strength training will increase relaxation times lead to unwanted fibre switching. Doing strength training in the wrong sequence does not help as well.

[prophet]

@martn76

People seem to suggest that type II fibres can not become slow or express slow MHC. Prolonged strength training akin to bodybuilding WILL lead to type IIa becoming type IIc. This unwanted hybrid will express a fast IIa MHC bound to type Ic MHC. The innervation of the muscle (determined by the CNS) WILL become slow. Prolonged bodybuilding methods without periods of rest and switching of strength training methods will cause this. The muscle fibre will slow in its ability to relax, this may even lead to slower sprint times. Type IIx ARE useful, the reason they transform leftwards to type IIa is due to thermodynamic efficiency. Basically type IIx/b can not “turnover” phospates and sugar fast enough because they lack the ability to utilise oxygen to turn by products back to phosphate and glucose.

Speed training on the other hand leads to slow to fast type IIa MHC conversion being and fast type IIx MHC expressing type IIa MHC. In other words an increase in type IIa occurs where as in strength training an increase of type IIc occurs. Whether you want to believe this or not these are the disconcerting findings of numerous papers I have come across. Yes the CNS is king but it loves efficiency and efficieny means slower innervation frquencies, an affinity to slower MHCs and light chains.

The point I am trying to make is that too much strength training will increase relaxation times lead to unwanted fibre switching. Doing strength training in the wrong sequence does not help as well.

martn, could u post the links or the reference to these studies?

[PowerManDL]

@martn76

People seem to suggest that type II fibres can not become slow or express slow MHC. Prolonged strength training akin to bodybuilding WILL lead to type IIa becoming type IIc. This unwanted hybrid will express a fast IIa MHC bound to type Ic MHC. The innervation of the muscle (determined by the CNS) WILL become slow. Prolonged bodybuilding methods without periods of rest and switching of strength training methods will cause this. The muscle fibre will slow in its ability to relax, this may even lead to slower sprint times. Type IIx ARE useful, the reason they transform leftwards to type IIa is due to thermodynamic efficiency. Basically type IIx/b can not “turnover” phospates and sugar fast enough because they lack the ability to utilise oxygen to turn by products back to phosphate and glucose.

No, the innervation won’t change. That’s the key point here. If you have a reference showing otherwise, please provide it.

Any fiber conversion that takes place is peripheral, not central, and is due to changes in MHC expression. If you train slow, you become slow. This is not a function of central factors downregulating. The predominance of literature shows that performance is related to neural factors, not peripheral. MHC expression is merely a function of this. Hybrid fibers co-expressing type II and type I isoforms are a function of training, as is any MHC expression.

Additionally, MHC isoforms are provided energy by a like isoform of ATPase. Again, if you have a reference showing that the IIx isoform interacts with the bioenergetic systems in any way besides providing ATP to the myofibril, please provide it.

Speed training on the other hand leads to slow to fast type IIa MHC conversion being and fast type IIx MHC expressing type IIa MHC. In other words an increase in type IIa occurs where as in strength training an increase of type IIc occurs. Whether you want to believe this or not these are the disconcerting findings of numerous papers I have come across. Yes the CNS is king but it loves efficiency and efficieny means slower innervation frquencies, an affinity to slower MHCs and light chains.

Type IIx isn’t found in any fibers except those that are detrained or unused.

Feel free to provide references showing that strength training shifts fibers in a way that provides negative gains in strength performance. I would be most interested to see them.

It seems you are trying to claim that the body will find a way to be more efficient at a specific activity by becoming less efficient at that activity. Slower innervation frequencies assumes that no heavy loads are being used. Maximal stress on the nervous system, be it from maximal weights or from repeated-effort methods, does not involve slow innervation frequencies. Further, speed of contraction and neural innervation “speed” are two different things governed by two completely separate systems. Neural firing frequency is a result of muscular tension developed, via load or acceleration. The shortening velocity of MHC is related to its chemical structure.

The point I am trying to make is that too much strength training will increase relaxation times lead to unwanted fibre switching. Doing strength training in the wrong sequence does not help as well.

Nevertheless, you are still treating fiber switching as a causal factor in performance increase or decrease, which it is not.

[fast11_12]

Thanks Martn76,

I really do want to thank you man. I feel way so much relaxed now. I’m following about the right sequance in training and I was so happy with the results until I was confused with the start of this topic. Now I feel much better and more confident. I do believe in the fact of conversion. May be I have nothing to support. But I have learned that anything in this life will have to adapt at one point if stressed enough. Anything. Thats what I believe.

Thanks again man. Take care

[martn76]

@PowerManDL

No, the innervation won’t change. That’s the key point here. If you have a reference showing otherwise, please provide it.

Any fiber conversion that takes place is peripheral, not central, and is due to changes in MHC expression. If you train slow, you become slow. This is not a function of central factors downregulating. The predominance of literature shows that performance is related to neural factors, not peripheral. MHC expression is merely a function of this. Hybrid fibers co-expressing type II and type I isoforms are a function of training, as is any MHC expression.

Additionally, MHC isoforms are provided energy by a like isoform of ATPase. Again, if you have a reference showing that the IIx isoform interacts with the bioenergetic systems in any way besides providing ATP to the myofibril, please provide it. Strength training DOES cause chemical changes that can affect innervation frequencies.

Type IIx isn’t found in any fibers except those that are detrained or unused.

Feel free to provide references showing that strength training shifts fibers in a way that provides negative gains in strength performance. I would be most interested to see them.

It seems you are trying to claim that the body will find a way to be more efficient at a specific activity by becoming less efficient at that activity. Slower innervation frequencies assumes that no heavy loads are being used. Maximal stress on the nervous system, be it from maximal weights or from repeated-effort methods, does not involve slow innervation frequencies. Further, speed of contraction and neural innervation “speed” are two different things governed by two completely separate systems. Neural firing frequency is a result of muscular tension developed, via load or acceleration. The shortening velocity of MHC is related to its chemical structure.

Nevertheless, you are still treating fiber switching as a causal factor in performance increase or decrease, which it is not.

Training causes chemical changes in the muscle caused by feedback form the nervous system. I had the same views so I hunted down some of the academics who carried out this research for their interpretations and expert advice. This is what I am relying on, not postulations or my own views but cutting edge ideas from those in the know.

Feel free to provide references showing that strength training shifts fibers in a way that provides negative gains in strength performance.

The 100m is not a strength event it is about speed and speed endurance not a strength performance.

[prophet]

@martn76

The 100m is not a strength event it is about speed and speed endurance not a strength performance.

Not a strength event??? :eek: :eek: Charlie?

[PowerManDL]

@martn76

Training causes chemical changes in the muscle caused by feedback form the nervous system. I had the same views so I hunted down some of the academics who carried out this research for their interpretations and expert advice. This is what I am relying on, not postulations or my own views but cutting edge ideas from those in the know.

I realize this. One has only to look at the calcineurin/calmodulin pathway to realize that neural action is a causative factor in fiber type shifts.

However, that pathway’s activation and expression only reinforces my point-- calcineurin activates the strongest in fibers in a state of disuse. In other words, those fibers expressing MHC-IIx. It appears that the mere use of fibers causes the shift away from the IIx isoform.

[martn76]

@prophet

Not a strength event??? :eek: :eek: Charlie?

Sprinting is not a pure strength or strength speed event. On a biometer scale it lies more towards speed. You need cyclical explosive muscular strength for the acceleration and cyclical explosive reactive strength for top speed speed maintenance phase, but it is less of a strength activity than say weight lifting or the throwing events.

Sprinters need to be generally strong, but the event can not be classified as just a strength event. If that was the case then we could all do lots of strength training and just run fast. On a biomotor scale its dominant skills, are more towards speed than strength.

I am not saying you do not need strength qualities, just making the point that sprinting is not a strength event.

[prophet]

@martn76

Sprinting is not a pure strength or strength speed event. On a biometer scale it lies more towards speed. You need cyclical explosive muscular strength for the acceleration and cyclical explosive reactive strength for top speed speed maintenance phase, but it is less of a strength activity than say weight lifting or the throwing events.

Sprinters need to be generally strong, but the event can not be classified as just a strength event. If that was the case then we could all do lots of strength training and just run fast. On a biomotor scale its dominant skills, are more towards speed than strength.

I am not saying you do not need strength qualities, just making the point that sprinting is not a strength event.

Sounds much better, thanks for clarifying the post!