Behavioral Properties of the Musculotendinous Unit

1) extensibility: ability to be

Behavioral Properties of the Musculotendinous Unit

2) elasticity: ability to return to

parallel elastic component -

series elastic component -

Behavioral Properties of the Musculotendinous Unit

3) irritability: ability to

4) ability to develop tension: (the contractile component of

muscle function)

Behavioral Properties of the Musculotendinous Unit

Parallel Elastic

ComponentSeries Elastic Component

Contractile Component

From a mechanical perspective, the musculotendinous unit behaves as a contractile component (muscle fibers) in parallel with one elastic component (muscle membranes) and in series with another elastic component (tendons).

Structural Organization of Skeletal Muscle

How are muscle fibers organized?

• parallel fiber arrangement:

•pennate fiber arrangement: short fibers attach to

Parallel vs pennate

Parallel vs Pennate

Structural Organization of Skeletal Muscle

Comparison of fiber architecture

•Effective force to tendon: •parallel __ pennate

•fibers per unit volume:•parallel __ pennate

•joint ROM:•parallel __ pennate

Structural Organization of Skeletal Muscle

What is a motor unit?

• single motor neuron and all fibers it innervates

• considered the functional unit of the neuromuscular system

• innervation ratio (# of fibers per motor neuron) dictates fine vs gross control

Structural Organization of Skeletal Muscle

Structural Organization of Skeletal Muscle

Fast twitch fibers both reach peak tension and relax more quickly than slow twitch fibers.

Tw

itch

Ten

sion

Time

FT ST

Skeletal Muscle Fiber Characteristics

TYPE IIAType I Fast-Twitch Type IIB

Slow-Twitch Oxidative Fast-Twitch Oxidative Glycolytic Glycolytic

CHARACTERISTIC (SO) (FOG) (FG)Contraction Speed slow fast fast

Fatigue rate slow intermediate fast

Diameter small intermediate large

ATPase concentration low high high

Mitochondrial high high lowconcentrationGlycolytic enzyme low intermediate highconcentration

Skeletal Muscle Function

How are motor units (MUs) recruited?• slow twitch (ST) fibers are easier to activate than fast twitch (FT) fibers• ST fibers are recruited first• increasing speed, force, or duration (fatigue) of movement involves progressive recruitment of MUs with higher activation thresholds (i.e. FT)

Skeletal Muscle Function

Skeletal Muscle Function

Muscles apply tension at origin and insertion

Actions of muscles dictated by:

•

•

Muscle tries to bring attachment points closer

Skeletal Muscle Function

What terms are used to describe types of muscle contractions?

• concentric:_________, muscle __ resistance

• eccentric: _________, muscle __ resistance

• isometric: _________, muscle __ resistance

Skeletal Muscle Function

What roles are assumed by muscles?• agonist:• antagonist:

• stabilizer:

• neutralizer:

Stabilizing scapula

Neutralizing

Qualitative anatomical analysis

• Divide the activity into phases• Identify joints involved and joint

movements• Determine type of contraction

– Against gravity (__) or with gravity (__)?– Increasing (__) or decreasing (__) velocity?– Overcoming resistance (__) or giving with

resistance (__)?

• What muscle(s) primarily active?

Posterior CompartmentHamstring

Skeletal Muscle Function: which muscles need to be active?

What joint motion?What muscles active and what type of contraction in each example?

What phase?What type of contraction?

Skeletal Muscle Function

What are characteristics associated with muscles that cross more than one joint?• active insufficiency:

• passive insufficiency:

Skeletal Muscle Function

Factors Affecting Muscular Force Generation

The force-velocity relationship for muscle tissue: When resistance (force) is negligible,

Velocity

Forc

e(Low resistance, high contraction velocity)

Factors Affecting Muscular Force Generation

The force-velocity relationship for muscle tissue: As the load increases,

Velocity

Forc

e

isometric maximum

Factors Affecting Muscular Force Generation: length-tension curve

Factors Affecting Muscular Force Generation

The length-tension relationship: Tension present in a stretched muscle is the sum of the active tension provided by the muscle fibers and the passive tension provided by the tendons and membranes.

Ten

sion

Length (% of resting length)

50 100 150

Active Tension

Passive Tension

Total Tension

Factors Affecting Muscular Force Generation

What is electromechanical delay? (force-time relationship)• time between arrival of a neural stimulus and tension development by the muscle

Factors Affecting Muscular Force Generation

Twitch vs tetanusTemporal vs spatial summation

Muscular Strength, Power, and Endurance

How do we measure muscular strength?•

Muscular Strength, Power, and Endurance

What factors affect muscular strength?• tension-generating capability of the muscle tissue, which is in turn affected by:

•

•

•

Muscular Strength, Power, and Endurance

What factors affect muscular strength?• moment arms of the muscles crossing the joint (mechanical advantage), in turn affected by:

• •

Muscular Strength, Power, and Endurance

What is muscular power?• the product of muscular force and the velocity of muscle shortening • the rate of torque production at a

joint• the product of net torque and angular velocity at a joint

Where does peak power occur

Muscular Strength, Power, and Endurance

What is muscular endurance?

• the ability of muscle to exert tension over a period of time• the opposite of muscle fatigability