underactivity

un·der·ac·tive

U5049650 (ŭn′dər-ăk′tĭv)adj. Characterized by insufficient or abnormally low activity: an underactive area of the brain.
un′der·ac·tiv′i·ty (-ĭ-tē) n.

underactivity

(ˌʌndərækˈtɪvətɪ) ninsufficient activity