Skeletal Muscle Structure and Function

What are muscle biopsies used to study?

Muscle enzyme activity, glycogen, capillary density, and fiber characteristics.

What are the three main muscle fiber types?

Type I (slow), Type IIa (fast oxidative), Type IIx (fast glycolytic).

What determines a person's muscle fiber type?

Genetics, hormones, and training habits.

What are the contractile and metabolic properties used to identify fiber types?

Speed, force, myosin ATPase activity, oxidative enzymes, and motor neuron type.

Which fiber type has the highest endurance?

Type I (slow-twitch).

Which fiber type fatigues the fastest?

Type IIx.

What does oxidative capacity depend on?

Number of mitochondria, capillaries, and myoglobin.

What determines contraction speed?

Myosin ATPase activity.

What determines maximal force production?

Muscle cross-sectional area (CSA).

What determines maximal power output?

Force × velocity.

What is muscle fiber efficiency?

How much energy a fiber uses to produce force.

What motor neuron controls Type I fibers?

α2 motor neuron.

What motor neuron controls Type II fibers?

α1 motor neuron.

What does Henneman's size principle state?

Motor units are recruited from smallest to largest as more force is needed.

What is asynchronous firing?

Motor units taking turns during submaximal contractions.

What is synchronous firing?

All motor units firing together during maximal effort.

What factors influence muscle force production?

Muscle size, contraction type, recruitment, velocity, length, and fiber type.

How does muscle architecture affect performance?

Short thick muscles create more force; long muscles contract faster.

What is pennation angle?

The angle of muscle fibers relative to the tendon.

What are the three types of muscle actions?

Concentric, isometric, and eccentric.

Which muscle action produces the most force?

Eccentric.

Which muscle action uses the most energy?

Concentric.

What are the two main components of strength gains?

Neural adaptation and contractile protein adaptation.

What changes occur during neural adaptation?

Increased motor unit recruitment, synchronization, rate coding, and reduced inhibition.

When do neural adaptations occur?

During the first few weeks of training.

What is hypertrophy?

Increase in muscle size due to protein synthesis.

What protein limits muscle growth?

Myostatin.

What are the two main types of hypertrophy?

Transient and myofibrillar (and possibly sarcoplasmic).

Which fiber type experiences the greatest absolute hypertrophy?

Type II fibers.

What is hyperplasia?

Increase in number of muscle fibers (not proven in humans).

What causes exercise-induced muscle cramps?

Either electrolyte depletion or altered neuromuscular control.

How does passive stretching relieve cramps?

It activates Golgi tendon organs, causing relaxation through the inverse stretch reflex.

Which fibers are more efficient?

Type I slow-twitch fibers.

Which fibers generate the most power?

Type IIx fast glycolytic fibers.

Which adaptations occur before visible muscle growth?

Neural adaptations.