Question

a rock climber grasps onto a ledge on a rock wall how do the bones and muscles interact to allow him to hold on?
1: all of the muscles in his are contract to hold his arm in position
2:his arm muscles work in pairs so that the one contracts while the other one relaxs to hold his arm in position
3:his arm muscles work independently of each other to hold his arm in position
4:all of his are muscles relax to hold his arm in position