There is a group of exercises, called Kegel exercises (named after the doctor that developed them), that can help you to strengthen the muscles that -- among other things -- control your sex organs....
thighmaster, or any excercise the provides resistance while squeezing your legs together.the most efficient way is to keep your body completely parallel, lying down being the simplest task.
Voluntary muscles are skeletal muscles (under somatic control) and involuntary muscles involve the heart, smooth muscles and anything under autonomic control.