Changes in Force of Muscle Contraction

A comprehensive set of vocabulary flashcards based on lecture notes regarding the types of muscle contraction, fiber classification, motor unit dynamics, and muscle pathologies.

Concentric contraction

A type of isotonic contraction where the muscle produces tension and shortens, such as the biceps brachii during the upward phase of an exercise.

Eccentric contraction

A type of isotonic contraction where the muscle produces tension and lengthens, slowing the lowering of the forearm and controlling elbow extension.

Isometric contraction

A contraction where the muscle develops tension and stays the same length with no movement, such as holding a weight still.

Slow-oxidative fibers (Type I)

Also known as red muscle fibers, these have a small diameter, many capillaries and mitochondria, high myoglobin content, and use oxidative phosphorylation for ATP.

Fast-glycolytic fibers (Type IIb)

Also known as white muscle fibers, these have a large diameter, high glycogen content, high myosin ATPase activity, and use glycolysis for quick ATP synthesis.

Type IIa fibers

Intermediate fibers that have high myosin ATPase activity and high both oxidative and glycolytic capacity.

Motor Unit

The functional unit of skeletal muscle activity consisting of one motor neuron and all the muscle fibers it innervates.

Recruitment

The stimulation of additional motor units to increase the strength of contraction, serving as a large-range adjustment of muscle activity.

Starling law

The principle stating that, within limit, the strength of muscle contraction is directly proportionate to the initial length of the muscle.

Passive tension

The tension exerted by the physical properties of elastic elements when an unstimulated muscle is progressively stretched.

Active tension

The amount of tension generated specifically by the contractile process, calculated as the difference between total tension and passive tension.

$L_{\text{max}}$ (Optimal length)

The sarcomere length between $2 - 2.2\,\mu m$ at which active tension is maximal due to the maximum number of cross bridges formed.

Force-Velocity Relationship

The relationship where the velocity of shortening is inversely related to the load; velocity is maximal ($V_{\text{max}}$) at zero load.

Multiple fiber summation

Increasing the intensity of muscle contraction by increasing the number of motor units contracting simultaneously.

Frequency summation

Increasing the intensity of muscle contraction by increasing the frequency of contraction, which can lead to tetanization.

Complete tetanus

A sustained contraction with no relaxation between stimuli because action potentials are so close that $Ca^{2+}$ does not get re-sequestered in the SR.

Treppe (Stair-case phenomena)

A successive increase in the amplitude of contractions when a rested muscle is stimulated with constant intensity, caused by warming up and increased $Ca^{2+}$ concentration.

Muscle Hypertrophy

An increase in muscle fiber diameter due to an increased amount of contractile proteins and cross bridges, typically resulting from short duration, high intensity exercise.

Muscle Atrophy

A decrease in muscle size and contractile proteins (actin and myosin) occurring due to damage to the motor nerve supply.

Muscle Fibrillation

Fine, irregular contractions of individual fibers that are invisible to the naked eye but recordable by electromyography, caused by denervation hypersensitivity.

Muscle Fasciculation

Jerky, visible contractions of a group of muscle fibers (motor unit activity) resulting from pathological discharge of spinal motor neurons.