Intensive Care Unit Acquired Weakness (ICUAW) describes muscle weakness that occurs in around 40% of patients during an intensive care stay. The morbidity and mortality of these patients is significantly increased over a 5-year period. The aim of this study is to investigate the combined effect of early enteral high-protein nutrition and early muscle activation on muscle atrophy in critically ill patients. The study will include 40 patients (20 intervention, 20 observation) with requirement for enteral nutrition at time of inclusion. In the intervention group the maximum possible level of mobilization is carried out and muscles are activated twice a day using neuromuscular electrical stimulation (NMES). The nutrition plan of the intervention group is based on the applicable guidelines for intensive care medicine with exception of increased protein intake. The control group receives therapy without deviating from the standard according of the DGEM guideline. The study aims to show that the decrease in muscle mass is significantly less than in the control group (primary hypothesis) via ultrasound of the rectus femoris muscle and in case of given consent muscle biopsy. As secondary hypothesis it is examined whether the combination of early high protein intake and muscle activation improves muscle strength and endurance.