Imagine tiny swimmers that break the rules of classical physics—welcome to the world of human sperm. 
A groundbreaking study led by Kyoto University’s Kenta Ishimoto reveals that sperm don’t follow Newton’s third law (“every action has an equal and opposite reaction”) when propelling themselves through the viscous fluids of the reproductive tract (Republic World).
Instead of relying on passive bending, sperm flagella inject energy directionally, creating an “odd elasticity”: internal, non‑reciprocal forces that push certain parts of the tail harder than others. Researchers captured this with a new metric, the odd‑elastic modulus, showing a precise match between injected energy sites and resulting motion (Republic World).
This discovery not only revolutionizes our understanding of cellular locomotion but also paves the way for real‑world innovations. Biomedical engineers can now design biomimetic microswimmers—tiny devices that mimic sperm’s strategic motion—to deliver drugs or perform diagnostics inside the body. In fertility research, measuring odd elasticity could help diagnose why some sperm fail to swim efficiently (Republic World).
In essence, human sperm are living proof that biology can bend the laws of physics—and with this insight, science is one step closer to mastering motion at the microscopic scale.
Source: Republic World
Credit: Shubham Verma, Republic World
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