Dr. Squat - Dr. Fred Hatfield

Slow twitch fibers don't produce high amounts of force. They produce low amounts of force, but can do so for extended periods of time.

Ok, so you say they are maxing out on both, which set would you say would be fatiguing them more ??? Thus putting out less and less force ??? Thus more tenstion on these muscle fibers ???

Wayne

It was once believed that there was only 2 types of fast twitch fibers (IIA and IIB), recently however a more complete continuum has been established and it looks like this:

IIC -- IIAC -- IIA -- IIAb -- IIAB -- IIaB -- IIB

The more on the right of the spectrum a fiber is the higher is it's speed of contraction and contractile power and the lower it it's endurance.

The fibers on the left of the spectrum are less powerful but more enduring. Now, with strength training all the fibers have a tendency to "move to the right" (except the IIB, which are destroyed with prolonged training), that is they increase their speed and strength of contraction but become less enduring. With endurance training the opposite happens.

Of course these changes happen after prolonged systematic training, it is not an overnight thing.

There is a possibility that with a lot of aerobic training that IIC fibers can be converted into IC fibers (ST fibers spectrum IA -- IC), however IIC and IC fibers do seem to be very similar in their properties so it is not sure if that convertion happen.

POINT: In the weight room, go with the type II fibers! Always!

No...... fibers and their response to training have not changed.

Only our knowledge of them have.

Hi all and thx for the comments, only speed read them, not much time till later.

What if I changed the question slightly, as someone is saying you can work the slow muscle fibers harder at slow speeds. which set will produce more overall tension to the slow muscle fibers, also fatigue or work the slow muscle fibers harder. And make them try and produce more force output.

I think it is the faster set, and always lift fast, but was wondering if there are any experts out there for comments ???

The power/strength overall output in the faster/slow reps and sets.
Lets calculate how much power/strength I would be used on both rep speeds. Distance weight moved 1.85 M.

Since we are using the metric system, we will first need to convert the mass of the barbell into kilograms (200 lb ÷ 2.2 = 91 kg).

Secondly, to determine the force we will need to figure out what the weight of the barbell is (W = mg = 91 kg x 9.81 m/s² = 892 kg.m/s² or 892 N). Now, if work is equal to Force x distance then, U = 892 N x 1.85 m = 1650 Nm.

We can calculate that lifting a 200 lb barbell overhead a distance of 1.85 m required 1650 J of work.

You will notice that the time it took to lift the barbell was not taken into account.
Let us only add up the positive part of the lift.

The concept of power however, takes time into consideration. If for example, it took .5 seconds to complete the lift, then the power generated is 1650 J divided .5 s = 3300 J/s.

If it took 2 seconds to complete the lift, then the power generated is 1650 J divided 2 s = 412.5 J/s.

Slow set,
412.5 x 6 = 2475Joules.

Fast set,
3300 x 25 = 99000Joules

Thank you for your time.

Wayne

Todd
What did I say wrong? I don't want to go around stating something that isn't true, like a total idiot!

### Ya'll are discussing slow twitch fibers with regards to "power" and 75% and 85% intensities.

That makes no sense! That's like discussing speed training for turtles. Or saying that if Manny the Marathoner improved his squat from 185 lbs. to 425 lbs. that he would shave a half hour off of his marathon time. Or slow tempo power cleans. They just have no place in the same sentence or discussion. It's not applicable.

I E-mail Roger M. Enoka, Ph.D. on the subject, and he gave some very interestin things.

One important point to emphasize in these types of discussions is the concept of slow and fast twitch muscle fibers. Unfortunately, this terminology is misleading because there are not two (or three) types of muscle fibers; rather, there is a continuous distribution in every muscle from the fibers with slow contractile kinetics through to those with fast kinetics. Because there are not distinct types of muscle fibers, it is not possible to design an exercise program that stresses either "fiber type".

A more appropriate functional distinction between muscle fibers is the force at which the motor units are activated during a muscle contraction, which is known as recruitment threshold. Motor units with low recruitment threshold can be either slow or fast twitch, whereas motor units with high recruitment thresholds are all fast twitch. But, recruitment thresholds decrease with contraction speed so that all motor units in a muscle are activated when rapid contractions are performed with loads 40% of maximum.

The force that a muscle must exert to move a load depends on two factors: the mass of the load and the amount of acceleration imparted to the load. The number of muscle fibers recruited during the lift increases with the speed the lift.

The rate at which any motor unit, low or high threshold, can discharge action potentials is not maximal during slow contractions. As contraction speed increases, so does discharge rate for all motor units.

The number of muscle fibers activated to lift a weight depends on two factors: (1) the amount of weight; and (2) the speed of the lift. Although more muscle fibers are activated during fast lifts, they are each generating MORE force. We know this because the rate at which the muscle fibers are activated by the nervous system increases with contraction speed.

Although your question seems relatively straight forward, it is not. Despite the popularization of the terms slow and fast muscle fibers, the characteristics of muscle fibers are not so black and white. Human muscle fibers are often classified as types I, IIa, and IIx. This distinction is NOT based on contraction speed (slow or fast) but is based on the activity of an enzyme that is related to contraction speed. When the enzyme activity is assessed with an histochemical stain, the fiber types appear quite distinct: black, grey, and white. When the enzyme activity is quantified, however, there is a continuous distribution of enzyme activity across the population. Furthermore, muscle fiber size (a measure of force capacity) varies continuously across the population and in some cases type I ("slow") fibers are actually the biggest.

I do not know how much work is performed by the different fiber types in the two scenarios you describe. I don't think this has been measured. The closest muscle physiologists have come to answering your question is to measure the size of muscle fibers in individuals who perform different types of training. The most common finding is that it is the intermediate fiber type (type IIa) that experiences the biggest increase in size (strength) in individuals who perform conventional weight lifting (heavy loads, slow reps) and body building (lighter loads, fast reps) training. Neither type of training appears to have a significant effect on the size of types I and IIx fibers.

Cheers.

Roger M. Enoka, Ph.D.
Professor and Chair
Department of Integrative Physiology
University of Colorado

Wayne

Umm, I have a few questions here...

"The most common finding is that it is the intermediate fiber type (type IIa) that experiences the biggest increase in size (strength) in individuals who perform conventional weight lifting (heavy loads, slow reps) and body building (lighter loads, fast reps) training. Neither type of training appears to have a significant effect on the size of types I and IIx fibers."

First, I concur that IIa fibers hypertrophy the most, as these are the ones most apt to be involved in fiber fusion.

But who says that heavy weights/slow reps is "conventional" for lifters? And who says that lighter loads/fast reps is "conventional" for bodybuilders?

High reps should, in fact, be done slowly, and heavy loads should, in fact, be done explosively. That is EXACTLY 180 degrees from what the author states is "conventional.

Ugh!

BTW, I wish someone would teach me how to format my text...I like to make bold characters, insert images, italicize, etc. Someone help!

Fred, here are the details...

http://drsquat.com/filter/tips/1#filter-bbcode-0

This isn't happening, it only thinks it's happening.

cool! Now let's try an image...