The general aim of an ICU respiratory rehabilitation programme is to improve the patient's measured quality of life. It can be done by applying advanced therapeutic modalities in order to improve the remaining functions and to decrease the patient's dependency as well as the risks associated with an ICU admission. A number of physiological changes involve all the body systems as a consequence of a bed-rest period and play an important role in the weaning failure of ventilated patients. Inactivity muscle mass declines from the first week of ICU admission, as well as the muscle's ability to perform aerobic exercise. The respiratory muscles strength and endurance decreases, also the ventilatory pump and the cardiovascular response to exercise may be alterated. Disorientation, and disfunction of the Central Nervous System may occur. The aim of this review is to analyse the usefulness of skeletal and respiratory muscle training in improving strength, endurance and decreasing dyspnea at rest and during exercise and the role of rehabilitation in obtaining maximal functional capacity of ICU patients.