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Updated: Jul 7, 2025

Biophysical Characterization of Flagellar Motor Functions
Published on: January 18, 2017
Viscous Loading Regulates the Flagellar Energetics of Human and Bull Sperm
Farin Yazdan Parast1, Shibani Veeraragavan1, Avinash S Gaikwad2,3
1Department of Mechanical and Aerospace Engineering, Monash University, Clayton, Victoria, 3800, Australia.
Abstract:
The viscoelastic properties of the female reproductive tract influence sperm swimming behavior, but the exact role of these rheological changes in regulating sperm energetics remains unknown. Using high-speed dark-field microscopy, the flagellar dynamics of free-swimming sperm across a physiologically relevant range of viscosities is resolved. A transition from 3D to 2D slither swimming under an increased viscous loading is revealed, in the absence of any geometrical or chemical stimuli. This transition is species-specific, aligning with viscosity variations within each species' reproductive tract. Despite substantial drag increase, 2D slithering sperm maintain a steady swimming speed across a wide viscosity range (20-250 and 75-1000 mPa s for bull and human sperm) by dissipating over sixfold more energy into the fluid without elevating metabolic activity, potentially by altering the mechanisms of dynein motor activity. This energy-efficient motility mode is ideally suited for the viscous environment of the female reproductive tract.
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