The present invention concerns a method for obtaining a functional parameter of a muscle having a part, the method comprising the steps of: a) applying ultrasound waves to the muscle, b) collecting the ultrasound waves retrodiffused by the muscle at a plurality of times, to obtain collected ultrasound waves, c) determining a first plurality of values representative of stiffness values of one part at a first plurality of times by using the collected ultrasound waves, d) determining a second plurality of values representative of deformation values of said part at a second plurality of times by using the collected ultrasound waves, and e) deducing at least one functional parameter based on the first plurality of values and the second plurality of values. The invention also concerns a corresponding device.