Fig. 5

Examples of image sequences of skeletal intra-muscular contraction patterns from a cross-sectional image plane A of the biceps brachii muscle at a constant low force level. B Represents a simulated (in silico, domain A) image sequence, and in C its corresponding variance map (Var map), computed as the variance of the time signals at each pixel in the image-sequence. D Represents an experimental (in vivo, domain B) image sequence, and E its corresponding variation map. In both sequences, the oscillating behaviour of different spatial regions can be seen (putative contractions of motor units). The experimental images presented different spatial features as compared to the simulated ones. The time between consecutive frames is here 2 ms and images show colour-coded tissue velocity