Severe critical illness is often complicated by Intensive Care Unit - Acquired Weakness (ICU-AW), which is clinically characterized by bilateral and symmetrical limb weakness and is related to a myopathy and/or axonal polyneuropathy. ICU-AW affects between 25% to 60% mechanically ventilated patients more than 7 days and is associated with increased in and post-ICU mortality, with delayed weaning from mechanical ventilation and with long-term functional disability. Most patients who develop an ICU-AW have been admitted for a sepsis episode and the main risk factors of ICU-AW include the severity of critical illness, immobilization, hyperglycemia and the use of some medications including steroids and neuromuscular agents, although this is somewhat controversial.