Lesson 4 - Skeletal Muscle Fiber Types

What characteristic of a muscle fiber determines its peak tension? Explain.

*Contractile Force* -Related to the size of the muscle fiber (larger muscle = more force = higher peak tension) -Fast Twitch are generally larger muscle fibers than Slow Twitch. Therefore they have more sarcomeres = more contraction = greater peak tension.

Describe how skeletal muscle adapts to detraining.

-*Increase in Type IIx* (you are fat and out of shape, so your body helps you out by giving you fast twitch muscle for a rainy day) -Loss of muscle mass (sarcopenia) and strength

Describe how skeletal muscle adapts to strength training.

-Increase # of Type IIa muscle fibers -Decreased # of hybrid muscle fibers -Hypertrophy of muscle -Increase in actin and myosin (more contraction)

Describe how skeletal muscle adapts to aerobic training.

-Increase Mitochondria (ability to utilize oxygen for energy) -Increase Myoglobin -Increase in Capillary-to-Fiber ratio -Increase in Type I muscle types -Decreased # of hybrid muscle fibers -A little bit of hypertrophy, but not as much as strength training

Understand the concept that muscle characteristics lie on a continuum.

-Muscle fibers can transform from one type to another on the continuum -All muscle fibers contain more or less of each characteristic

Name the three key characteristics that contribute to the oxidative capacity of a muscle cell.

1. *Capillary-to-Fiber Ratio* 2. *Mitochondrial Density* (The use of oxygen to create energy takes place in the mitochondria. More mitochondria = more oxidative capacity) 3. *Myoglobin* (myoglobin binds to oxygen. More myoglobin = more oxygen to bind and help create energy in the mitochondria)

What are the different names used to describe the three pure fiber types?

1. Type I (slow-twitch) 2. Type IIa(fast-twitch) 3. Type IIx (fast-twitch)

What is DOMS? What kind of exercise results in DOMS?

DOMS: Delayed Onset Muscle Soreness Any lengthening type contractions cause DOMS

Define a hybrid muscle fiber.

Fiber types that are a mix between Type I and Type II Example: Type I/IIa or Type IIa/IIx

Describe the repeated bout effect.

If you do a workout that results in Delayed Onset Muscle Soreness (DOMS), repeating that same workout a few days or weeks later would result in less muscle soreness than the first bout of exercise.

Explain how force of contraction of intact whole skeletal muscle is increased above that of a single twitch.

More motor units are recruited

Describe what is meant by skeletal muscle is highly plastic.

Plasticity: The capacity for adaptive change. The ability to alter gene expression.

How does the size of the motor neuron relate to recruitment of motor units?

Smaller motor units are recruited before larger motor units

How does capillary-to-fiber ratio affect the delivery of oxygen to muscle?

The more capillaries (blood vessels) that are available, the more oxygen will get delivered to the muscle cell.

What characteristic of a muscle fiber determines its time-to-peak tension? Explain.

Time-to-Peak Tension is the time from when the stimulus occurs to peak tension. -*Shortening Velocity* corresponds to Time to Peak tension -Shortening Velocity is the speed at which a muscle fiber can shorten

Which of the skeletal muscle fiber types are least abundant in human skeletal muscle?

Type IIx

Tell how muscle fibers are typed.

You remove a small piece of muscle from the whole muscle, wash it, freeze it, and then analyze it.

The generally accepted model for the enlargement of skeletal muscle fibers as a result of strength training is that _____. a. existing muscle fibers get bigger causing enlargement of the whole muscle b. there is an increase in the number of muscle cells causing enlargement of the whole muscle c. there is an enlargement of type II muscle fibers but not type I muscle fibers d. there is an enlargement of type IIx muscle fibers but not type IIa muscle fibers

a

What does "rate coding" refer to? a. The increase in force of contraction due to high frequencies of stimulation b. The rate at which muscle fibers fatigue during contractions c. The rate at which muscle fibers produce force (i.e., shortening velocity) d. The classification of muscle fibers based on time-to-peak tension.

a

Which muscle fiber type is always presented on the left of the continuum of muscle fiber types? a. Type I b. Type IIa c. Type IIx d. Cardiac muscle cells

a

As a result of strength training, which muscle fiber type typically increases? a. type I b. type IIa c. type IIx d. type IIa and IIx

b

The force of contraction of single twitches of an isolated skeletal muscle fiber _____. a. can be graded b. cannot be graded

b

What does "number coding" refer to? a. The nomenclature used to describe muscle fibers (i.e., type I, type IIa, type IIx). b. The increase in force of contraction due to recruitment of more motor units c. The number of different muscle fiber types in a motor unit d. The number of muscle fibers in a motor unit

b

Which of the following is another accepted name for a type I muscle fiber? a. Aerobic fiber b. Slow oxidative (SO) c. White fibers d. Slow glycolytic (SG)

b

During the downward movement of the squat exercise, the quadriceps are contracting _____. a. concentrically b. statically c. eccentrically

c

Which of the following is the correct order of motor unit recruitment (first to last)? a. Type IIx, type IIa, then type I. b. Type IIa, type IIx, then type I. c. Type I, type IIa, then type IIx. d. Type I, type IIx, then type IIa

c

Which of the following is true about the color of skeletal muscle fibers? a. ST fibers are whiter (more pale) than FT fibers. b. ST fibers are the same color as FT fibers c. ST fibers are more red than FT fibers d. All the muscle fiber types are the same color.

c