Pectorals, triceps, biceps and deltoids. These muscles are located in your shoulders, arms and thorax. Method
Lie down on the bench, make sure your comfortable as you do not want to be adjusting during reps. Grip barbell roughly 8 inches apart, again make sure your grip is secure and comfortable. Lower the bar slowly and smoothly directly over your chest and in the same rhythm up to the top again. Try to remain smooth in your transaction from the down to the up as if you are doing it in a jerking action you my cause injury. Your back should remain in contact with the bench at all times and your arms should not lock. Notes
Your biceps and pectorals are agonist when your on the way down with bar and on the way up they are antagonist. your biceps are synergist with your triceps because when your biceps are agonist your triceps are antagonist and vice versa. Deltoids are agonist when the bar is on the way up and antagonist when the bar is on the way down.
Standard sit ups consist of lying flat on your back with your legs bent up at the knees in a triangle shape. You then bring your chest up too your knees, this should be done with your arms across you chest because if they are behind your head it is easy to pull your head up and strain your neck. Obviously you then reverse the action going back down trying to keep your back slightly of the ground each time as to feel the full effects of each sit up.
The rectus abdominis is agonist on the way up in the standard sit up and is antagonist on the way back down. This means that on the way up it shortens to allow the movement to take place and then on the way down the muscle will relax again. The best example of agonist and antagonist movements is in a twist sit up. This is because when your internal oblique is agonist your external oblique is antagonist and vice versa.
Rectus femoris, vastus...