Peak propulsion forces and swimming velocities of different microswimmers (n =15 microswimmers for each group). Boxes plot minimum, first quartile, median, third quartile and maximum values. The sperm-motor trains, consisting of multiple tubes, show no significant difference from the one-tube sperm-motor in the propulsion force measured at a speed of 0 m/s. This is consistent with the fact that the elastic force of the cantilever picospring accurately equals the propulsion force provided by the sperm when there is no fluid drag (otherwise the drag force is typically proportional to velocity with a coefficient of friction determined by geometry). Thus, in the static state, the influence of the volume and friction of the synthetic part of the sperm-motor can be neglected on the picospring-based measurement of the sperm's propulsion force.
