Fig. 6

Spz velocity during circling. a Velocity heatmaps of a sharp (top) and slight turn (bottom). The start of the tracks is marked with a green dot and the end with a red dot. The velocity of the spz fluctuated along the tracks. b The velocity of the spz tracks depicted in A are plotted over time, including a line for the average velocity per 15 s. c The velocity distribution of the spz circling on a glass surface in the different formulations. In PBS enriched with BSA, the spz did not circle. In HBSS and RPMI enriched with BSA, the spz circled on average with a velocity of 1.6 µm/s. In the solutions enriched with FBS, the spz circled faster, on average: 2.5 µm/s (p = 0.002; Mann–Whitney U test). Although the median velocity differed between the solutions enriched with BSA and FBS, the velocity ranges were the same (p = 0.796; Mann–Whitney U test)