Muscle

Anatomy of muscle

Belly of the muscle contains fibers; tendons attached to bones. The bone which remains relatively fixed in the movement is called the “origin” and the bone which moves is called the “insertion.” These are relative terms which change depending on the motion.

Functions of muscle

Muscles are either undergoing concentric shortening or eccentric lengthening. Both terms indicate the use of muscle to oppose gravity. In shortening, the upward force generated by the muscle is used to overcome it. In lengthening, the upward force is less than gravity, so it is used as a “controlled brake” (Source: Google Gemini).

Types of application, or: use of the functions of muscle

• Isotonic (rare): shortening of muscle under a constant load
• Isometric: holding still under resistance

Muscle as an actor, or: Muscles in relation to one another

An agonist is a muscle which is primarily responsible for movement (and is aided by muscles called synergists). An antagonist muscle opposes these movements, which is helpful in limiting movement and smoothing it.

Stretching

Stretching has to be done slowly, otherwise the muscles will tense and resist stretching.