Rarely in the human body do muscles work
in isolation. Most of the time, especially with the skeletal muscles,
pairs of muscles (and sometimes even more than pairs) work together to
create smooth and diverse movements. One typical model for muscle
functioning is the push/pull muscle pattern, such as can be found in the
biceps/triceps pairings of the arms. In truth, muscles can only
contract to exert force. They can also relax, but this doesn't exert a
force, so it is necessary for the body...