Fig. 6. (A) Variation in whole wingbeat, upstroke and downstroke durations across flight speeds (inter-individual means ± S.D.; N=5 for each speed) as measured via muscle lengthening and shortening. Consistent with the modest change in wingbeat frequency versus speed (Fig. 5), wingbeat duration varies slightly but significantly (P<0.05; Table 2) with speed. Changes in wingbeat duration across speeds is due entirely to changes in upstroke duration, as downstroke duration does not vary significantly with speed (P>0.1; Table 2). (B) Variation in wingbeat duration measured via a 125 Hz, three-dimensional kinematic reconstruction. Although the general pattern is similar to that shown in A, the relative durations of upstroke and downstroke have shifted such that downstroke is shorter than or equal to, rather than longer than or equal to, upstroke.