can't read euler angles and acceleration by mpu6050evb

Hello,
I configured the library for mpu6050a2. I want to read the euler angles and the acceleration by calling the function inv_get_euler_angles_x and the function inv_get_linear_accel_float. Before calling these two functions, I have firstly called umplInit and umplStartMPU. There is no error but they give me always the initial values. Il seems that they read nothing from the fifo. (I don't use the ustore in the project)
Any idea? Thanks.