Fig. 1

The flagellar beat pattern of human sperm displays a second-harmonic component. a Four snapshots of a tethered human sperm that rotates clockwise around the tethering point with rotation velocity Ω(t). Each color corresponds to a different snapshot taken at the indicated time. White and gray lines below the blue snapshot show the tracked flagellum at consecutive frames acquired at 2 ms intervals. Scale bar represents 5 µm. b Rotation velocity of the cell around the tethering point. The gray area indicates the time interval that is further analyzed in c, d. c Kymograph of the flagellar curvature during approximately 10 beat cycles (0.5 s). The curvature corresponding to the two horizontal lines is plotted in d. d Curvature of the flagellum at segments located at 15 μm (blue) and 25 μm (red) from the head. The curvature displays a sawtooth-like profile. e Power spectrum of the curvature at 15 μm and 25 μm. The fundamental frequency is ω_o = 20 Hz