Structure and function: muscle fiber type

aside from muscle fiber type what factors regarding muscles contribute to athletic success?

1. cardiovascular function 2. motivation 3. training habits 4. muscle size

describe how a muscle generates force

1. motor unit recruitment: type I to Type II (less to more) 2. frequency of summation (rate coding) - Twitch, summation, and tetanus.

describe the relation between muscle force and power. what is a training application of this concept?

1. peak force is not peak power. power is a combination of force and speed and is greatest 20% of max force. 2. a training application: to train fro power the weight must be reduced to 20% of the max force and done at speed.

What are the characteristic differences of Type I and Type II muscle fibers.

1. slow or fast myosin ATPase 2. type I and II have different types of myosin 3. Type II has a more highly developed SR -- Ca2 ions are released faster, and VO is 3-5 times faster. 4. different sizes of motor units

what is the optimal length for muscles fibers to generate maximal force?

100-130% of the muscle resting length (2-2.25µm sarcomere length), as this provides for the greatest cross-bridging interactions, and therefore maximum force.

What is the peak tension of type 1 muscle fibers?

110 ms

What is the peak tension of Type II muscle fibers?

50ms

Rate coding: Summation

A series of three stimuli in rapid sequence, before complete relaxation from the first stimulus, can elicit an even greater increase in force or tension. This is termed summation. - or Summation is the addition of post-synaptic potentials, that all add up to reach the threshold

muscle power vs muscle force

Force= strength power= (Force x Distance)/time

describe how type II fibers function during exercise.

General functioning - Fatigue quickly - produce ATP anaerobically Type IIa - produce more force but fatigue faster that type I fibers - used for short, intense endurance (i.e 1600 m run) Type IIx - seldom used for everyday activites - used for short explosive sprints (100 m run

what factors determine muscle fiber type?

Genetic factors: - which type of motor neuron innervates the fiber affect the differentiation. Training factors: - can induce 10% change in fiber type - differentiates endurance training, strength training, and detraining.

isometric contraction

Muscle contracts but there is no movement, muscle stays the same length

list everything that affects force generation.

The amount of muscle force developed is dependent on... 1. the number and type of motor units activated 2. the frequency of stimulation of each motor unit 3. the size of the muscle 4. the muscle fiber and sarcomere length (L-T relationship) 5. the muscle's speed of contraction (F-V relationship)

order the muscles from most powerful to least.

Type 2x, type 2a, type 1. (comes from motor units, SR, etc.)

what is the difference in motor unit size between type I and II muscle fibers?

Type I motor unit: smaller neuron, <300 fibers Type II motor unit: larger neuron, >300 fibers

what muscle fiber type would you expect to be most predominate in an endurance athlete? power athlete?

Type I; Type II

what are the two forms of type II muscle fibers?

Type IIA (fast oxidative glycolytic) and Type IIx (fast glycolytic)

how do muscles increase the amount of force applied? a. more fibers inside the motor are recruited b. more motor units are recruited c. type IIx muscles are recruited immediately when more force is needed d. more sarcomeres are recruited.

b. more motor units are recruited

How can the eccentric force-velocity be utilized in training?

because you can bear more load in an eccentric contraction you can increase the adaptation accordingly to over come plateau. this is termed an "eccentric workout" and they are more risky.

length-tension relationship

effect of muscle fiber length on the amount of tension the fiber can develop.

T/F all muscle fibers reach peak force at ~20% of peak power?

false

what is the effect of fast and slow myosin ATPase?

fast: fast contraction cycling slow: slow contraction cycling

describe how type I fibers function during exercise.

have high aerobic endurance: - can maintain exercise for prolonged periods - require Oxygen for ATP production - recruited for low-intensity aerobic exercise and daily activities. efficiently produce ATP from fat and carbohydrates.

force-velocity relationship

illustrates muscle force as a function of the speed of contraction. - concentric relationship: as the load increases velocity decreases. - Eccentric relation: as the load increases the velocity increases.

isotonic: eccentric contraction

muscle lengthens while maintaining tension - cross-bridging forms but the sarcomere lengthens

isotonic: concentric contraction

muscle shortens as it maintains tension - sarcomere shortens; filaments slide together

finish this sentence: as the intensity of the activity increases the....

number and type of muscle fibers recruited increases beginning with type I fibers.

size principle

order of recruitment of motor units is directly related to the size of their a-motor neuron. (smallest to largest)

rate coding (frequency of summation)

process by which the tension of a given motor unit can vary from that of a twitch to that of tetanus by increasing the frequency of stimulation of that motor unit

Rate coding: Tetanus

sustained maximal tension due to high frequency stimulation

Opisthotonos

tetanic spasm in which the head and tail are bent dorsally and the back is arched

how does the order of recruitment apply to endurance exercise?

the body begins by recruiting type I muscles predominately since endurance activities are done at a submaximal capacity. the body will also begin recruiting type II fibers according to the size principle as they fatigue. finally when type I and type IIa muscles are exhausted the body will recruit type IIx.

why does the body recruit the smallest muscles first?

the body is efficient and only fires the muscles that it needs to to accomplish a task.

what part of the body typically begins to atrophy first?

the distal portions of the body

Rate coding: Twitch

the effect of a single stimulus

Muscle Fiber Recruitment

the progressive recruitment pattern of muscle fibers, dependent on the intensity of activity or exercise from type I, to type IIa, to type IIx.

what muscle is purely composed for type I muscle fibers?

the soleus

principle of orderly recruitment

the theory that motor units generally are activated on the basis of a fixed order of recruitment, in which the motor units within a given muscle appear to be ranked according to the size of the motor neuron

what muscle is commonly used fro muscle biopsies?

the vastus laterales

what has the greatest cause of the different contraction speeds of type I and type II muscle fibers.

this results from the different types of myosin ATPase. - Type I have a slow Myosin ATPase - Type II have a fast Myosin ATPase ATP is split faster in Type II fibers allowing for faster cross bridges.

T/F all muscle fibers reach peak power at ~20% of peak force?

true

T/F one training adaptation is an increase in rate coding?

true

t/f The ability of the muscle to develop force also depends on the speed of contraction.

true

t/f type IIa and type IIx motor units contain more muscle fibers than type I motor units do

true

t/f type IIa muscle fibers have a high recruitment threshold than type I muscle fibers?

true, this is according to the orderly recruitment priciple and the size principle since type IIa motor neurons are bigger than type I.

when aging what type of motor units are typically lost?

type II motor units

how does a motor unit vary the amount of force it exerts? what are the names for this?

varying the frequency it is stimulated at; this is referred to as rate coding and takes three forms: twitch, summation, and tetanus.

Rahbdomyolysis

when damaged muscle tissue releases its proteins and electrolytes into the blood. These substances can damage the heart and kidneys and cause permanent disability or even death.

approximately what percentage of muscle fibers in the average muscle are Type 1?

~50%