Muscle Physiology: Tension, Performance, and Muscle Types

Vocabulary flashcards covering Modules 10.7, 10.8, and 10.9: motor units, muscle contractions, fiber types, physical training adaptations, fatigue, and muscle tissue comparisons.

Motor Unit

A single motor neuron and all the muscle fibers it innervates; when the neuron fires, all fibers within the unit respond and produce tension.

Fine Control

Motor control achieved via small motor units to provide precise movements.

Gross Control

Motor control achieved via large motor units to provide powerful contractions.

Motor Unit Recruitment

The activation of a small number of motor units at the initiation of a contraction, followed by the activation of additional motor units as greater force is required.

Muscle Tone

A baseline level of tension present in a resting muscle due to background motor unit activity; provides posture, joint stability, and readiness to respond to movement.

Isotonic Contraction

A contraction that causes the muscle to change in length as tension rises.

Concentric Contraction

An isotonic contraction that occurs when muscle tension exceeds the resistance, causing the muscle to shorten.

Eccentric Contraction

An isotonic contraction that occurs when muscle tension is less than the resistance, causing the muscle to lengthen.

Isometric Contraction

A contraction where muscle tension cannot overcome the resistance, resulting in no change in muscle length.

Length-Tension Relationship

The mechanical principle demonstrated when a flexed wrist shortens the muscle, an extended wrist keeps the muscle at natural length, and a hyperextended wrist stretches the muscle.

Type I Muscle Fibers

Small-diameter, slow-twitch oxidative fibers that contract slowly, produce less force for longer durations, possess high numbers of mitochondria and myoglobin, have a well-developed blood supply ('dark muscle'), and predominate in postural muscles.

Type II Muscle Fibers

Large-diameter, fast-twitch glycolytic fibers that fatigue quickly, have high myosin ATPase activity, rely primarily on glycolytic catabolism for ATP, and have fewer mitochondria, less myoglobin, and a less extensive blood supply ('white muscle').

Endurance Training

Physical conditioning involving long duration, more repetitions, and less weight; increases mitochondria and blood supply to produce high amounts of ATP, primarily utilizing Type 1 fibers.

Resistance Training

Physical training characterized by quick bursts of energy using Type 2 fibers, resulting in decreased mitochondria, lower ATP amounts, and decreased oxygen relative to endurance training.

Disuse (Atrophy)

A condition resulting from lack of muscle use that leads to a decrease in mitochondria, strength, and endurance.

Muscle Fatigue

The decline in muscle ability caused by depletion of key metabolites (glucose, glycogen, CP), decreased oxygen, accumulation of lactic acid, decreased blood pH, and environmental heat leading to dehydration.

Recovery Period

The post-exercise phase during which ventilation increases to restore oxygen levels, clear lactic acid, and raise blood pH back toward normal.

Smooth Muscle

Spindle-shaped, nonstriated muscle tissue with a differing number of nuclei that uses actin, myosin, and the powerstroke mechanism to generate tension.

Cardiac Muscle

Striated, autorhythmic (pacemaker) muscle tissue containing T-tubules, shorter cells, a single nucleus, and intercalated discs.

Intercalated Discs

Specialized structures in cardiac muscle cells that facilitate the rapid transmission and production of action potentials between adjacent cells.