At a macroscopic level of large bending motions, a continuum medium model is proposed describing a microtubule as an elastic rod. Compressional and shear deformations are excluded as less relevant biophysically. When the microtubule is subjected to a constant bending force, it is found that the dynamics of the angular deviation, with respect to the rectilinear configuration of the microtubule, is governed by a Sine-Gordon Equation. Particular analytical solutions of this equation are found which describe kink and anti-kink bending modes which may propagate at various subsonic speeds along the length of the microtubule. Kinetic energies of these modes are calculated for different propagation velocities and compared with thermal and ATP hydrolysis energies. Viscous damping is shown to be negligible for long microtubules and fast moving bending deformations.