Muscle-force generation

What is a latent period

A very brief delay between stimulus and contraction

What does the latent period represent

The time required for excitation, excitation-contraction coupling, and tensing of elastic components of muscle (generating internal tension)

What is the contraction phase

The time when muscle generates external tension

What does the contraction phase represent

That the force generated can overcome the load and cause movement

What is the relaxation phase

The time when tension declines to baseline

What does the relaxation phase represent

When the SR reabsorbs calcium, myosin releases actin and tension decreases, this phase takes longer than contraction

The entire twitch duration varies between what

7ms and 100ms

What does subthreshold stimuli represent

There is no muscle contraction at all

What does at threshold stimuli represent

There was enough stimuli to produce a contraction

What does maximal stimuli represent

All of the available motor units were recruited due to the amount of stimuli

Even if the same voltage is delivered what causes different muscle twitches

The different stimuli cause varying strength

What does a muscles starting length do

It influences the tension generated

Does muscle fatigue have a role on twitch strength

Yes muscle fatigue plays a role in twitch strength

What happens with warmer muscles

There enzymes work faster

What does a muscle cell’s hydration levels do

Influence cross bridge formation

What does increasing the frequency of stimulus delivery do

It increases the tension output

Different task require what of muscle contraction

They require variable strength

What does stimulating the nerve with higher voltages do

It produces stronger contractions

Higher voltages do what

They excite more nerve fibers which stimulate more motor units to contract

What is recruitment/ Multiple motor units

The process of bringing more motor units into play with stronger stimuli

Why does recruitment occur

It occurs according to the size principle

What is the size principle

Weak stimuli (low voltage) recruit small units, while strong stimuli recruit small and large units for powerful movements

Muscles contract more vigorously as stimulus strength does what

Increases above threshold

What happens when contraction force is precisely controlled by recruitment

It activates more and more muscle fibers

Does anything happen after maximal stimulus

No there is no increase in the force of contraction

What kind of twitches do low frequency stimuli produce

They produce identical twitches

What do higher frequency stimuli produce

Temporal (wave) summation

What happens with Temporal (wave) summation

Each new twitch rides on the previous one generating higher tension

What does the partial relaxation between stimuli result in for Temporal (wave) summation

It results in fluttering and incomplete tetanus

What do unnaturally high stimulus frequencies cause

A steady contraction called complete (fused) tetnus

Where do we see unnaturally high stimulus frequencies

In lab experiments

What is isotonic muscle contraction

The muscle changes length with no changes in tenson

What does isotonic contraction allow you to do

It allows you to move the load

What are the two types of isotonic muscle contraction

Concentric contraction and Eccentric contraction

What is concentric contraction

The muscle shortens as it maintains tension

• Ex: Lifting weight

What is eccentric contraction

The muscle lengthens as it maintains tension

• Slowly lowering a weight

What is isometric contraction

The muscle produced internal tension but external resistance cause it to stay the same length

What does isometric contraction prevent

The movement of a load

What is isometric contraction important for

Postural muscle function and antagonistic muscle joint stabilization

What phase happens at the beginning of contraction

Isometric phase- The muscle tension rises but the muscle does not shorten

What happens when the tension overcomes the resistance of the load

The tension levels off

What phase happens as muscle begins to shorten and move the load

The isotonic phase

What is muscle tone

The constant, slightly contracted state of all muscles

What does muscle tone do

It keeps muscles firm, healthy, and ready to respond

What is muscle tone a result of

Spinal reflexes- Groups of motor units alternatively activate in response to input from the stretch receptors in muscle