(a–p) RMA regression suggested positive linear relationships between m.s.e. (y axis) and Froude number in 11 out of 16 subjects, and CV (z axis) and Froude number in 15 out of 16 subjects. However, R2 and p-values (r2 > 0.75, p = <0.05) strongly support linear increases in variability with Froude in only four subjects when assessed by m.s.e. in four subjects, and in 11 subjects when assessed by CV (table 3). Froude number is (Fr = v2/g × LL), where v2 is speed squared, g is gravity (9.81 m s−2) and LL is each subject's leg length measured from the superior apex of the iliac crest to the where the heel meets the floor.