Deconditioning is adaptation of an organism to less demanding environment, or, alternatively, the decrease of physiological adaptation to normal conditions. Decondition may result from decreased physical activity, prescribed bed rest

Bed rest

Bed rest is a medical treatment involving a period of consistent recumbence in bed. It is used as a treatment for an illness or medical condition, especially when prescribed or chosen rather than resulting from severe prostration or imminent death...

, orthopedic cast

Orthopedic cast

An orthopedic cast, body cast or surgical cast, is a shell, frequently made from plaster, encasing a limb to hold a broken bone in place until healing is confirmed...

ing, paralysis

Paralysis

Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...

, aging, etc.
A particular interest in the study of deconditioning is in aerospace medicine, to diagnose, fight, and prevent adverse effects of the conditions of space flight.

Deconditioning due to decreased physical effort results in muscle loss, including heart

Heart

The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

 muscles.

Deconditioning due to lack of gravity or non-standard gravity action (e.g., during bed rest

Bed rest

Bed rest is a medical treatment involving a period of consistent recumbence in bed. It is used as a treatment for an illness or medical condition, especially when prescribed or chosen rather than resulting from severe prostration or imminent death...

) results in abnormal distribution of body fluids.