Fig. 4. Kinematic variables as a function of time. Body movement for 1.2 tail beats is shown for one individual moving with the typical pattern observed during steady swimming. Thick lines show trends found by least-squares curve-fitting and thin lines denote 95% confidence intervals (calculated by Matlab version 5.2, Mathworks). See Results for the functions fitted to these data. Negative values for curvature are directed concave-left and positive values are concave-right. (A) Graphs of curvature as a function of body position at five different instants separated by intervals of 0.2 tail-beat cycles. The values at each instant for concave-right curvature (
CR), concave-left curvature (CL) and the position of the inflection point (si) define the shape of this step function. (B,C) Variation in CR (B) and CL (C). Note that the amplitude of changes in concave-right curvature (CR) is smaller than the amplitude of concave-left curvature changes (CL). Oscillations in CR are of opposite sign and are half a tail beat out of phase with the changes in CR. (D) Variation in the inflection point in curvature (si) with time demonstrates a linear propagation of the inflection point down the length of the tail. (E) The angle between the trunk’s midline and the first anterior tail segment (see Fig.1) with time in phase with CR.
