Graphical representation of MTrPs and IZ location in the upper trapezius according to the ACS in 48 subjects. A) Active MTrPs are represented as green circles and latent as white circles, and the colours indicate MTrP spatial densities (dark red spot indicates high trigger point density). B) IZ distribution, colour represents IZ density (dark blue area indicates high IZ density). C) Each IZ loction is represented by different colours link IZs detected on the matrix columns. AC, acromial angle; C7, spinous process of the seventh cervical vertebrae.