Apparatus comprises an acceleration unit, a processing unit and a display for continuous real time monitoring. The acceleration unit is attached or held by a body region of a mammal comprises a 3D-acceleration sensor and a wireless transmitter for transmitting a measurement signal provided by the acceleration sensor continuously. The processing unit processes the measurement signal continuously in a band of a medically defined movement of the body region, forms a movement index on the basis of a norm of values of acceleration in a first time window, and forms a value(s) of amplitude, and/or a value of frequency of the spatial movement of the body region on the basis of a power spectral density in second time window of a known duration. The display displays said movement index with said value of amplitude, and/or said value of frequency of the spatial movement continuously in real time.