Admission to the intensive care unit (ICU) with critical illness is typically associated with profound physical impairments including peripheral skeletal muscle wasting and dysfunction. These effects demonstrate a rapid onset from the point of ICU admission, affect those with higher illness acuity to greater levels, and contribute to the development of intensive care unit-acquired weakness (ICU-AW) defined as severe upper and lower limb muscle weakness. Clinically patients present with significant limitations in exercise capacity and performance of physical functional activities, with deficits persisting for many years following resolution of the original illness.