Reactivity and ST Fibers

Expert Discussion Biomechanics and Physiology
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Skeletal muscle histology and biochemistry of an elite sprinter, the African cheetah
Authors
T. M. Williams, G. P. Dobson, O. Mathieu-Costello, D. Morsbach, M. B. Worley, J. A. Phillips
Abstract

To establish a skeletal muscle profile for elite sprinters, we obtained muscle biopsy samples from the vastus lateralis, gastrocnemius and soleus of African cheetahs (Acinonyx jubatus). Muscle ultrastructure was characterized by the fiber type composition and mitochondrial volume density of each sample. Maximum enzyme activity, myoglobin content and mixed fiber metabolite content were used to assess the major biochemical pathways. The results demonstrate a preponderance of fast-twitch fibers in the locomotor muscles of cheetahs; 83% of the total number of fibers examined in the vastus lateralis and nearly 61% of the gastrocnemius were comprised of fast-twitch fibers. The total mitochondrial volume density of the limb muscles ranged from 2.0 to 3.9% for two wild cheetahs. Enzyme activities reflected the sprinting capability of the cheetah. Maximum activities for pyruvate kinase and lactate dehydrogenase in the vastus lateralis were 1519.00 - 203.60 and 1929.25-482.35 7mol minm1v·vg wet wtm1, respectively, and indicated a high capacity for glycolysis. This study demonstrates that the locomotor muscles of cheetahs are poised for anaerobically based exercise. Fiber type composition, mitochondrial content and glycolytic enzyme capacities in the locomotor muscles of these sprinting cats are at the extreme range of values for other sprinters bred or trained for this activity including greyhounds, thoroughbred horses and elite human athletes.

Keywords
Key words Cheetah · Fiber type · Mitochondrial volume density · Skeletal muscle · Sprinting

The extreme speed kings of nature do not support the above statement that Pakewi has quoted, however appealing.

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Thanks for sharing this study.
If slow twitch fibres are that important to sprinting, why do sprinters have the lowest percentage of ST fibres in the human population (exept paralysed individuals)?

Sprinters only need ST fibres for stabilisation, in the core inperticular.

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I meant the statement quoted by pakewi. Yes fast fiber is essential but more important is the correct type of training that leads to fiber conversion in favour of fast twitch.

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the weight ft ratio test works like this :

determine ur 1rm then with 80% of ur max c how many reps u can do. if u can’t do any more than 7 u probably have more than 50% ft , if u can do more than 12 u probably have less than 50% ft and if u do between 7 and 12 u probably have 50/50.

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:smiley: :cool: cheers man.

Also, i heard someplace, that fiber conversion needs to generally take place as a teenager, particually if you do sports as a teenager.
Now, as most of my sports as a teenager were of the aerobic sort, swimming, triathlons, roadrunners. with the odd Beach Sprints thrown into that mix, does that mean that the most of my transitional fibers transferred to ST fibers and cannot be RE-transferred to fast fibers? Or can they constantly be Re-transferred back and fro, to a degree?

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the law of reversibility says “if you don’t use it you lose it” meaning if u stop a certain stimulis 4 long enough ur body will reset 2 default value. provided u stop though.

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They can be transformed, that is they are adaptable ALL throughout our lifetimes, the level of adaptability depends on the individual. Your fiber make-up changes according to things like diet, level of activity illness, hormonal profile.

For example someone with a thyroid hormone near the upper limit of secretion of thyroxine will have a high percentage of fast fiber, just as someone with a high level of testosterone. Catecholamines also positively influence fast fiber.

Starving yourself or restricting your calorific intake will cause a left shift on the spectrum in favour of slower fiber MHC expression(slow intermediate fast).

Sprint training with long recovery has been shown to increase fast fiber make-up by a small amount but the magnitude may not be that important if say a 5% transformation to the right causes a large improvement in speed.

Endurance training is a potent way of transforming fast fiber to the left, but it must be added that the threshold of fast fiber recruit ment must be breached for this to occur.

Resistance training is a potent transformer of fast to slow…yes fast to slow… according to Staron et al. After approx 3 months there was NO type IIB fiber detected, but after a total cessation of training there was an OVERSHOOT in fast fiber. Yet it must be added that proper nutrition immmediately after training IMO will help to stop the fiber conversion in the wrong direction. What is fascinating to add is that type IIA is abundant in sprinters, maybe during the taper, a conversion of some of the fibers to the right in favour of type IIB occurs to aid performance.

Some lucky individuals have the ability to cause what physiologists call uni-directional conversion where the extremes of their fiber spectrum convert to type IIA.

Heart attack victims have a HIGH percentage of fast fiber probably due to lower oxygen concentrations in the blood.

In a study by Gunter Tidow, different types of strength training over relatively short periods (3-4 weeks) caused fiber conversions either to the left or the right. Hypertrophy causes conversion to the left and if prolonged will lead to NO fast fiber type IIB. Max strength training does not lead to much fiber conversion. Power training with intra-rest pauses between each rep of 5-12 secs (not like the continuos rythmic training of normal strength training) led to a fiber conversion to the right with 60% of RM loading.

Adequate rest between sessions also influences fast fiber favourably.

40% of fiber make-up can be influenced by training. Genetics accounts for 45% and these in most people can not be altered.

Originally Posted by arnie365
the weight ft ratio test works like this :

determine ur 1rm then with 80% of ur max c how many reps u can do. if u can’t do any more than 7 u probably have more than 50% ft , if u can do more than 12 u probably have less than 50% ft and if u do between 7 and 12 u probably have 50/50.

The test is flawed as it can be influenced by things such as caffeine intake as an example.

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He has changed and adpated those tests and those rep numbers a few times over the years and they vary depeneding on exercise and muscle group (from what I can recall just now).

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resistance training does’nt convert fast 2 slow, it converts fast 2 intermediate. intermediate is a variant of the fast twitch, that’s y it’s type IIa and IIb. one of the main differences is it has better endurance qualities, it’s a endurance ft fiber.

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I do not see any reason why to define “lucky” individuals shifting to fibers make ups less efficient BY DESIGN (IIA fibers are outperformed by Types IIB and I in their respective tasks anyway).

Doesn’t this make you think of anything really?

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Who or what group of people have 100% fast twitch fibres?

Post your answers here … I’ll post the answer in a bit …
:wink:

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Yes it does, type IIb to type IIa will convert eventually to type Ia. There are fibers that are hard wired and WILL NOT change further than intermediate but if the stressor is chronic enough it will occur in those muscles that are adaptable.

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Look at it this way, if you have a high percentage of slow fiber and there so NO possibility of them converting fully to type IIB, then its better to have type IIa increasing. Also those lucky people I am talking about who have bi-directional transformation to intermediate fiber will do well even under loads and volumes that would cause others to loose sprint and strength abilities or progression due to fiber fatigue and conversion to slow as a result of thermodynamic requirements. When loading is decreased these people are the most likely in the tapering phase to experience a RIGHT transformation to type IIB leading to an
overshoot and improvement in sprint speed.

Refering to the heart attack victims and applying to sports and athletes it would seem that in human sprinters, type IIA fibers are thermodynamically more desireable in sprint performance, as identified by Tidow et al and R S Staron et al and Esbjornsson M.

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Overfed lard arses…fatties. Of course this does not mean that they are not needed for sprinting

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:slight_smile:
Close - but not 100% FT

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Oh I give up come on let us know gotta go to bed LOL.

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Children in the womb and new-borns …

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so explain y an anaerobic exercise like resistance training will have an oxidative muscle adaption? ft muscles r the 1’s that hypertrophy not st. i have also seen the study, it’s type IIb 2 type IIa not type I and there is no type Ia the varients occur in ft fibers where u have type IIa, IIb, IIc, IIab, IIac and so on.

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kool, i did not know that! :cool:

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Its my “useless-but-interesting” piece of information for today!!!