Critically ill patients with a predicted prolonged ICU stay will receive neuromuscular electrical stimulation (NMES) of one quadriceps muscle. Whether the dominant or non-dominant side will be stimulated is chosen randomly by using opaque sealed envelopes. The patients will receive electrical stimulation for 1h for 7 consecutive days. The stimulated and non-stimulated side will be compared for it's thickness (by using ultrasound imaging), muscle strength if the patients are awake and cooperative (using the medical research council scale and handheld dynamometry) and a muscle biopsy will be taken. As a primary outcome the investigators hypothesize that electrical stimulation will preserve muscle mass with respect to the non-stimulated quadriceps. As secondary outcomes the investigators hypothesize that electrical stimulation can reduce muscle strength loss and leads to a better protein balance and thicker muscle fibers in the stimulated quadriceps.