Rectus Abdominis
Erector spinae
Erector spinae muscles
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.
The erector spinae
erector spinae group
Erector Spinae
erectus spinae
The erector spinae
Erector spinae
Erector Spinae are extensor muscles encompasing the neck and trunk. Extensor movement is antagonistic to flexor movement. Therefore, find a muscle of the neck and a muscle of the trunk that act as flexors. That should answer your question without giving away all of the milk and honey!
erector spinae group
Erector Spinae (Lower back)