Recruiting Fast Twitch Fibers

Interesting that the Beta-2 receptor binds beta agonists

in lung tissue to dilate the bronchioles in asthma.

What role does up and down regulation of the Beta-2

receptor play in the training adaptation. Do high

circulating levels of epinephrine and norepineprine in

runners/sprinters down regulate B2 receptors in asthmatic

lung. Glucocorticoids block loss of B2 receptors and

inactivation of the secondary effectors at the B2 receptor

(G protein). Does heavy training lower circulating

glucocorticoids, and affect the availibilty of B2 receptors.

THANKS to Phoenix and others for dispelling some hard-fought myths. Can someone get Hadd, Lydiard, JK, Snell etc to come on here and say: yeah, we were wrong, we were stating some theories as hard facts with very little scientific backing. (and I say this because in MANY places Lydiard or Hadd or JK would state categorically that ST fibers are recruited in long runs instead of saying something like: ?it is my belief that perhaps ST fibers are also recruited in long runs, but this has not been proven.? )

And this is nothing against long runs, or endurance training at all. Because of course these things are important to any runner. BUT NOT BECAUSE THEY MAKE YOUR PURE SPEED FASTER OR BECAUSE FT FIBERS ARE BEING RECRUITED. But because your endurance capacity, economy, & AT/LT become so high through such training, that you can run faster at all distances from 800 up, compared to if you had done very little mileage at all. And this is not against ALL that Lydiard states, because as others have shown on this thread, Lydiard felt that too much endurance work without proper speed work WILL ADVERSELY EFFECT ONE AT ALL PACES, AND IN KICKING.

And let?s even say that it WAS true that FT fibers on slow runs were recruited, and as Deak put it(and clearly he got this from JK) that ?after an hour and a half, an hour and 45 minutes, magical things happen. You start recruiting fast-twitch muscles. So, in essence, you?re doing a speed workout while going slow.? Let?s say that WAS true(and of course it is not)?..What would be wrong with doing lots of endurance work and only recruiting ST fibers, and at other times doing speed power work to simulate/recruit FT fibers and help your speed? Nothing I would think.

And if glycogen depletion of ST fibers was a great method for recruiting FT fibers, wouldn?t it be a proper recommendation to not eat much before/after workouts? That way, your muscles would always be fairly depleted, and you would get right to the FT fibers on your easy runs without wasting time, right? What's wrong with taking in lots of carbs/calories and fighting off depletion during workouts? Isn't that what ultra runners/Tour de France cyclists do...STAVE OFF depletion as long as possible?

Thanks Phoenix/others, and may Pseudo-Science Rest In Peace!

I would be careful not to throw the baby out with the bath water here. The fact does remain that the fast twitch fibers ARE depleted during a long run. This likely is some sort of an adaptation stimulus.

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About Beta-2 down regulation: I don't know much about this so I can't comment much. I do know that some have said prolonged used of beta-blockers while endurance training can upregulate the number of B-2 receptors and create a performance advantage when the use of the beta-blocker is stopped. One of the reasons why chronic killer interval training leads to a performance drop-off is likely the down regulation of B-2 receptors.

Epinephrine is potent bronchodilator. Epinephrine mists are used in medical centers to treat acute asthma and bronchitis. Anaphalactics carry a syringe around with epinephrine in it in case the ingest peanuts or the like. If they do they pop themselves with it, get a jolt that puts red bull to shame, and keep their airways from clamping shut.

Asthmatics can benefit from including some high intensity work in their warm-up because the epinephrine release can help facilitate bronchodilation. This would only be effective for mild cases of asthma.

So then, we should expect ultra runners to be the best 10K - Marathon runners?

Explain. I'm not quite sure how you are arriving at that conclusion.

Phoenix, could you explain in layman terms how glycogen depeletion leads to glycolysis in fast-twitch fibres? It's not like they need energy since they are not contracting right? I'm thinking any ATP required for basic cell processes would be quite insignificant and can be just derived from blood glucse.

I've not visited the message board for 3+ months as i was sick of the nonsense in most posts. However, this thread is extremely useful and as a coach I'm glad to have the references for further reading (and would agree that the Brooks text is the best out there). Thank you to those who took the time reference journal articles. Yet I can't help but wonder, why aren't useful threads like this one in such sort quantity on this board?

Disclaimer - Robert and Weldon, this is by no means aimed at the work you've done and continue to do to promote the sport and inform those who value track and field; the question is aimed at the members and contributors to the board, specifically those who use the board as vehicle for slander, gossip, etc.

Layman wrote:

Phoenix, could you explain in layman terms how glycogen depeletion leads to glycolysis in fast-twitch fibres? It's not like they need energy since they are not contracting right? I'm thinking any ATP required for basic cell processes would be quite insignificant and can be just derived from blood glucse.

The glycogen depletion leads to glycolysis not vice versa as you wrote above.

Explanation in Layman's Terms:

Exercise causes the release of a hormone called epinephrine from a part of the adrenal gland call the medulla. Epinephrine is the same thing as adrenaline. So, that jolt you get when startled--that's epinephrine.

Cells throughout the body have receptors that bind epinephrine. When these receptors bind epinephrine cellular processes are altered. One type of EPI receptor found on cells including skeletal muscle cells is called the beta-2 adrenergic receptor. (The word adrenergic comes from the word adrenal. The word adrenal means near the kidney: ad-renal.)

When EPI docks on the beta-2 receptors on skeletal muscle it triggers the break down of glycogen and the formation of lactate through a signaling pathway called the cAMP/PKA (cyclic AMP/Protein Kinase A) pathway. The epinephrine is causing the glycolysis.

The lactate released from the non-working muscles can be used as fuel by tissues throughout the body including sketetal muscle and heart. The heart is very good at using lactate for fuel becuase of it large number of mitochondria. The heart can be up to 8% mitochondria by weight. Well trained skeletal muscle can be ~2% mitochondria by weight, higher in slow twitch fibers and less in fast twitch fibers. Thus slow twitch fibers are much better at using lactate for fuel than fast twitch fibers. Lactate can be reconverted into glycogen in skeletal muscle and liver. Additionally the liver can convert it back into glucose for immediate release into the blood stream.

This system is beneficial because it allow the fast twitch fibers which are not suitable for use in endurance running to serve as a fuel tank for the slow twitch fibers. Hence even after the slow twitch fibers are glycogen depleted their energy supply can be maintained somewhat by lactate from the fast twitch fibers and glucose from the liver and fat.

Fasting empties the liver of glycogen but will NOT empty the muscles of glycogen. Another hormone called glucagon acts through the same cAMP/PKA pathway to cause glycolyis in the liver but the release of glucose into the blood. Glucagon becomes elevated while fasting. Skeletal muscle lacks glucagon receptors. So, the only way to access the skeletal muscle fuel take is by exercising.

But, do remember that the glycogen depletion occuring in fast twitch fibers that are not recruited on long runs is almost certainly an adaptation stimulus of some kind. Glycogen is a known inhibitor of one pathway for mitochondrial biogenesis. Purposely restricting food intake is to keep muscle glycogen low by not restoring muscle glycogen after workouts in hope of better stimulating mitochondrial growth is probably a bad idea. To stay healthy you should try and recover in every legal way possible. A study just came out showing that interleukin-6, a potent stress chemical with sometimes harmful effects, is released from skeletal muscle if a training session is started with extremely glycogen depleted muscles. However, starting with adequate glycogen and then depleting during the run didn't seem to have the same effect. So, the necessary pattern seems to be empty duing the run, but fill back up a some before the next run. This is really too new of a finding to say much though.

J Appl Physiol. 2003 Aug 22 [Epub ahead of print].

Interleukin-6 release from human skeletal muscle during exercise: relation to

AMPK activity.

MacDonald C, Wojtaszewski JF, Pedersen BK, Kiens B, Richter EA.

Human Physiology, Copenhagen Muscle Research Centre, Institute of Exercise and

Sport Sciences, University of Copenhagen, Copenhagen, Denmark.

Hope that helps. Exercise physiology and biochemistry is really quite interesting and applicable where it is really understood. I can tell you that we are just on the surface of understanding what is really going on. People like Lydiard et. al. are scientists in their own right. They made observations about training responses and explained them as well as they could. Sometimes they were right and sometimes they were wrong. Sometimes we are wrong today. Sometimes were are right.

CO-Runner wrote:

So then, we should expect ultra runners to be the best 10K - Marathon runners?

If these guys are doing incredibly long runs, then you would expect that many fast twitch muscle fibers are being recruited, as a result you would expect that ultramarathoners should be fast over much shorter distances, if this training theory is true.

Ultramarathoners likely have little to no fast twitch fibers, therefore are generally slow over shorter distances no matter what.

CO-Runner wrote:

CO-Runner wrote:

So then, we should expect ultra runners to be the best 10K - Marathon runners?

If these guys are doing incredibly long runs, then you would expect that many fast twitch muscle fibers are being recruited, as a result you would expect that ultramarathoners should be fast over much shorter distances, if this training theory is true.

This is the exact myth I am trying to dispell.

Simply put and striped down to it's basics:

The body will adapt specifically to the stimilus it is exposed to. If you run 50 mile training runs and 100 mile races then your body will adapt specifically to that stress and only that stress. You may have some transferable effects that will prove to be usefull in other events (like the marathon) but for an ultra runner to become a good 5k/10k runner then he'd have to train specifically for that 5k/10k and do some running at that speed.

Alan

I do see the benefit to the heart for long runs but see your point when it comes to the current line of thought. One thing that has puzzled me is if you are targeting increased density of capillaries, mitochondria, and enzymes for the actual motor units used in races why would you seek to do that by running so slow. The very little bit I can find about it suggests the motor units are quite different. See www.elitetrack.com/biomechanicsofrunning.pdf for what I am getting at. Would not something like Luiz's circuit training with long repeats and sprint drills used in the active recovery hit more useful motor units over a larger range of motion over the course of an hour?

I do not understand all of this. When I eat my fiber, I get a fast twitch, and I have to run.

Phoenix wrote:

CO-Runner wrote:

If these guys are doing incredibly long runs, then you would expect that many fast twitch muscle fibers are being recruited, as a result you would expect that ultramarathoners should be fast over much shorter distances, if this training theory is true.

This is the exact myth I am trying to dispell.

Phoenix,

No one here is saying that JUST running 2+hr runs will help your basic speed. You need to do basic speed work (60m/80m/100m/120m) inconjunction with your training program inorder for long runs to achieve anything in terms of speed improvement.

Trackhead,

Phoenix,

No one here is saying that JUST running 2+hr runs will help your basic speed. You need to do basic speed work (60m/80m/100m/120m) inconjunction with your training program inorder for long runs to achieve anything in terms of speed improvement.

I am well aware of that. Nowhere in this entire thread have I implied the above.

They may help your kick because you stayed more aerobic until the kicking has started. Snell outkicked everyone because of his stamina. Don't think for a second that long runs will improve your basic speed. They absolutely won't.

I agree whole heartedly that the ability to kick via endurance training results from staying more aerobic for a longer preriod of time than your competitiors and then being able to change gears.

But I'm not a professional on this matter. I don't have any formal education in exercise phys. Sure I've read books but I haven't been schooled in the subject.

Perhaps you should email Dr. Snell on the issue. When I spoke with him a few months ago he was more than helpful.

Phoenix - I concur with several of the other posters - THANKS. This is very interesting, inciteful, and even USEFUL!

At the risk of broadening this topic too much and getting off onto other subjects.....aren't your thoughts and beliefs more or less a vote for "multi-tier" type training systems.....or at least some sort of multi-tier hybrid?

It seems to me that its more of an issue of being able to utilize your sprint speed at the end of a race, as opposed to improving speed. Maybe more of a speed maintenance type of thing. Of course this isn't very useful for sprints, but it is very useful for being able to feel more comfortable at increased speeds towards the end of a race. Then that's where the plyos and neuromuscular training come in...which are also crucial to racing.