jaw
Synergists
Synergists help steady movements and fixators help stablize the prime movers origin.
Of all the muscles contracting simulataneously, the one that is mainly responsible for producing a particular movement is called the prime mover for that movement. The other muscles that help in producing the movement are called synergists. As prime movers and synergists muscles at a joint contract, other muscles, called antagonist muscles, relax.When antagonist muscles contract, they produce a movement opposite to that of the prime movers and their synergist muscles. -- I wrote kind of alot so you can under stand it just in case if you don't :)
Antagonists are muscles that work in the opposite direction from prime movers and synergists.
Synergists as well as fixator muscles.
your rectus abdominis is the prime mover in a crunch exercise or spinal flexion
femur
Rectus abdominis is the prime agonist and the superior and inferior oblique muscles are synergists. Erector spinae is an antagonist including a number of other muscles of the back.
prime movers : muscle that initiate a particular movement synergism : muscles that have the same action of the prime mover antagonist : muscles that come into play to oppose a certain movement
The atissimus obrsi abdominals is the prime mover in a sit up.
The Main muscles used when you do elbow curls are the bicep muscles.
Well it's first important to understand that muscles shorten. So you have a muscle that is longer when its relaxed, but then when you use that muscle it shortens pulling the bone(s) that it is attached to with it. So if you hold out your arm palm side up and then bend your elbow so your hand comes toward your shoulder, your biceps are shortening and causing the movement. Now when you reverse the movement and go back to your arm straight and your palm up, your triceps are shortening. There are many muscles that work this way in the human body. There are prime movers which preform a a function, and antagonists which do perform the opposite of that function. Also, there are synergists muscles which help the prime movers by performing the same movement as them or making sure that you don't perform an undesirable movement. Then there are fixators which are a type of synergists which hold bones still while the prime mover is contracting.