 Patients that are on mechanical ventilators in medical intensive care units MICU have extremely weak leg muscles. Currently there is no treatment to prevent or reverse this weakness. Treatments with a thigh muscle stimulator, called an All Stim 2, can improve leg muscle strength and help patients regain leg function after knee surgery. The purpose of the present study is to determine if treatments with the All Stim 2 device can also improve leg muscle strength in patients on mechanical ventilation. 