Strenous poses are found throughout Bacon's dismembered sketchbook. These pages show careful variations alongside switches of scale and medium. Among the identifiable sources are the split-second photographs from Eadweard Muybridge's 'The Human Figure in Motion' (1901) which Bacon much admired. 'Figure with Arms Swung Out' is taken from a runner preparing for a race, while the 'Figures with Left Arm Raised' (one traced from the other) derive from photographs of fencers. Dispensing with their contexts, Bacon made the figures' actions inexplicable even as they remained credible. The less easily deciphered 'Figure in Grey Interior' shows a structure around the figure which Bacon also used in contemporary paintings.