A system (100) for assessing a subject at risk of a soft tissue abnormality such as deep vein thrombosis (DVT), comprises a motion sensor (108) which is adapted to be fixed, in use, to a muscle (106) of the subject. The motion sensor includes a transmitter (206) configured to transmit a signal (400) representing motion of the sensor. A receiver (118) is configured to receive the signal from the transmitter of the motion sensor. A signal processor (112) is coupled to the receiver and configured to analyse first and second data sets received via the receiver from the motion sensor. The first and second data sets represent respective first and second oscillatory mechanical responses of first and second muscles of the subject resulting from mechanical stimuli. The analysis comprises determining first and second parameter sets characterising the first and second oscillatory mechanical responses, and comparing the first parameter set with the second parameter set to assess a possible presence of DVT in the subject.