Terminology & Definitions

Basic Definitions

Myo in the body relates to muscle. If it has myo as the prefix then we are looking at a structure involved in muscle anatomy or physiology. Examples include: myoglobin, myosin, myofibril, myofascia, myotatic...
Agonist refers to the primary mover of a muscle, such as the biceps in a bicep curl, or the triceps in a tricep extension. Antagonist refers to the opposite muscle, such as the biceps in a tricep extension.

It is useful to learn your muscles in agonist and antagonist pairs.

A synergyst assists the agonist muscle and or helps stabilise the joints through the movement. Synergysts will become active either as the agonist fatigues or as resistance increases and help is needed.

In the image you have the brachioradialis, rhomboids, and teres major - these muscles can act as synergysts to the brachialis, trapezius, and latissimus dorsi respectively.

A co-contraction is when two opposing muscle groups contract around a joint to increase stability.

In the image if the antagonist muscle were to contract at the same time then it would oppose the agonist and there would be no movement - this increases stability around the joint. Imagine how you might brace the muscles around your knees, hips and core as you prepare to ski down a hill, basically in a quarter squat position maintaining strength around all the joints. This is called co contraction.

All muscles connect to bone via tendons. We will call these attachment points origin (the proximal attachment), and insertion (the distal attachment). All muscles groups will have one insertion, but may have many origins.
Fascia is a layer of tissue which wraps around many differnt parts of the body. Myofascia refers to the layers which wrap around the muscle. There are three specific layers (epimysium, perimysium, & endomysium - knowing these individual layers will not make or break your exam).