SAITO, T, and OKI, F. The Strain-Energy Density Function of the Urinary Bladder. Tohoku J. exp. Med., 1982, 137 (4), 401-408 - In previous articles we proposed a finite deformation theory of the urinary bladder. The present paper is the third article in a series of these works. Our aim is to study more carefully the strain-energy density function W of the urinary bladder, because the determination of this function W is one of the central problems in the finite deformation theory of a hyperelastic continuum. We found that, except for an infinitesimally small deformation region where Hook's law is valid, the third term in W of the Valanis-Landel type takes much smaller values than the other two terms, so that this term can be neglected. Hence, the formula giving the true stress t₁ for the uniaxial extension test is reduced to the same one as the true stress t for the equal-biaxial extension test. This may be useful in practical applications. - neurogenic bladder; urodynamics; theory of elastic body; cystometrogram