Contraction

Muscle tension

Force exerted by contracting muscle on an object

Load

Force exerted by the object on the muscle, but only enough is generated to move the object. When moved, muscles experience both types of contraction (isometric and isotonic)

Muscle twitch

The muscle fibers contractile response to a single ATP

Has 3 phases, latent, contraction, and relaxation

Latent phase

E-C coupling starts

Contraction phase

Active cross bridges

Relaxation phase

Calcium returns to the SR and the number of cross bridges declines

All or none response

Each twitch generates equal force

Muscle tone

Sustained partial contraction that happens when theres another stimuli before the muscle relaxes fully, more cross bridges are added, or recruitment of motor units occurs.

Tetanus

No relaxation between stimuli

Recruitment

Increase in the number of motor units activated to achieve greater contraction force/strength

Threshold stimulus

The 1st stimulus where there is an observable contraction

Strength changes

Increase in stimulus frequency or strength of stimulation increases, which then causes the fiber tension to increase

Muscle fatigue

Physiological inability to contract despite stimulation that causes a decline in performance and alters muscle chemistry.

Caused by ion imbalances interfering with E-C coupling because AP is not conducted down into t-tubule, which stops the release of calcium

Leads to a buildup of potassium if there is prolonged, repetitive, high-frequency APs

Central fatigue

When less motor signals are issued from the brain

Exercise → amonia buildup → inhibit brain cells → decreased motor signals

Psychological fatigue

A type of central fatigue caused by depression, disease, being female, and genetic vulnerability

Recovery

Removal or conversion of lactic acid

Replace glycogen, ATP, and CP stores

Replenish oxygen reserves in the myoglobin

Super-compensation theory

The body's performance change after recovery from training or physical stress.