intransitive verb
Definition: To lose physical fitness or conditioning, often due to a lack of exercise or activity.
Example: After several months of inactivity, I began to decondition and felt weaker than before.
transitive verb
Definition: To make someone or something lose their physical fitness or to eliminate a learned response, often through lack of use or exposure.
Example: After several months of inactivity, he began to decondition and lost his athletic abilities.