The most common causes of generalized weakness are Deconditioning due to inactivity (disuse atrophy) resulting from illness or frailty, especially in older patients Generalized muscle wasting due to prolonged immobilization in an intensive care unit (ICU) —a condition called ICU myopathy Critical illness polyneuropathy (ICU neuropathy) Common myopathies (eg, alcoholic myopathy, hypokalemia, corticosteroid myopathy) Use of paralytic drugs in a critical care patient Table Fatigue Many patients report weakness when their problem is fatigue.