The sternocleidomastoid muscles are the ones that flex when the intercostals are flexed. This will also cause the scalene muscles to flex.
The gastronemius muscle is one of the calf muscles and it plantar flexes the foot or flexes the knee.
Internal Intercostals
Intercostals, sternocostals, subcostals
intercostals
You may be thinking of the diaphragm. There are others such as the intercostals.
gastrocin
it flexes and rotates the head
sternocleidomastoid
quadricep
i THE ILIOPSOAS
Voluntary muscles can be flexed.
Abductor muscle - moves a limb away from the midlineAdductor muscle - moves a limb towards the midlineExtensor muscle - increase the angle at a joint - extends a limbFlexor muscle - decreases the angle at a joint - flexes a limbPronator muscle - turns a limb to face downwardsSupinator muscle - turns a limb to face upwardsRotator muscle - rotates a limbIn the human body, these are the responsible muscles.*Muscles which move the thigh and their action*Gluteus maximus - Extends and rotates thigh laterally.Adductor longus - Adducts, medially rotates and flexes the thighAdductor brevis - Adducts, laterally rotates and flexes the thighAdductor magnus - Adducts, flexes, laterally rotates and extends the thigh.Rectus femoris - Extends knee and flexes hipVastus lateralis - Extends kneeVastus medialis - Extends kneeVastus intermedius - Extends kneeSartorius - Flexes knee. Flexes hip and rotates femur laterallyBiceps femoris - Flexes leg and extends thighSemitendinosus - Flexes leg and extends thighSemimembranosus - Flexes leg and extends thigh