Factors that influence muscle contraction

Strength

Force of muscle contraction that depends on the number of muscle fibers recruited, size of muscle fibers, frequency of stimulation, and the degrees of muscle stretch

Ideal length tension relationship

The initial length of the muscle when a stimulus is first applied will affect the force generated

Contractile force increases = more cross bridges are attached

Velocity

How fast

Duration

How long

Fast glycolytic

Fast-twitch muscle fibers that produce powerful contractions quickly but fatigue rapidly because they rely mainly on anaerobic glycolysis for energy

Low myoglobin, so light in color

Slow oxidative

Slow-twitch muscle fibers that contract slowly, resist fatigue, and use aerobic respiration (oxygen) to produce energy.

High myoglobin, so dark in color

Fast oxidative

The middle fibers

Fast-twitch muscle fibers that contract quickly, resist fatigue moderately well, and use both aerobic and anarobic for energy

Load effect on velocity and duration

Greater load = shorter and slower period of muscle shortening

Latent period increases with a greater load

Aerobic exercise

Endurance

More capillaries, mitos, and myoglobin

Slow oxidative fibers

Resistance

For large muscle

Increase fiber size, myofibrils, myofilaments, glycogen, and CT

Fast glycolytic fibers

Hyperplasia

An increase in the number of cells in a tissue or organ, causing it to grow larger.

Increases force generation

Formation of new muscle fibers

Testosterone

Stimulates muscle growth

Why men tend to develop larger muscles

Erythropoietin

Increased number of RBC’s to increase oxygen delivery to muscles, which enhances endurance

Steroid Hormones

Increase muscle mass

Can prematurely close growth plates and stunt growth in adolecent’s

Hypertrophy

An increase in the size of existing cells, causing a tissue or organ to become larger.

Increases force generation, actin, and myosin

Myofibrils split

Lengthening

Occurs alongside normal growth

Increase shortening capacity and max contraction velocity

Atrophy

Weakening and shrinking of a muscle

Caused by immobilization, loss of neural stimulation, injury, disuse, and decreased muscle preformance

Muscle repair and regeneration

1. Destruction

2. Inflammation

3. Repair

4. Remodeling or modeling

Destruction phase

The 1st phase

• Muscle fiber is damaged

• Necrosis (death) of damaged muscle tissue occurs

• Blood vessels may rupture, causing inflammation

Inflammation phase

The 2nd phase

• Macrophages and other immune cells enter the damaged area

• Dead tissue and debris are removed

Repair phase

The 3rd phase

• Satellite cells are activated

• Satellite cells divide (mitosis) and differentiate into myoblasts

• Myoblasts fuse to repair existing fibers or form new muscle fibers

Remodeling phase

The 4th and final phase

• New muscle fibers mature

• Connective tissue reorganizes

• Muscle regains strength and function