Fig. 11. (A) Forward-directed thrust per foot relative to forward swimming velocity, with higher thrust and velocity for synchronous kicks relative to asynchronous kicks. (B) Mass-specific momentum per foot relative to forward velocity and (C) duration of the power stroke, with the horizontal line in C representing the approximate average mass-specific momentum per foot for Rana esculenta calculated from fig. 3 in Nauwelaerts and Aerts (2003).