We describe the procedure for obtaining Hamiltonian equations on a manifold with so(k, m) Lie-Poisson bracket from a variational problem. This implies identification of the manifold with base of a properly constructed fiber bundle embedded as a surface into the phase space with canonical Poisson bracket. Our geometric construction underlies the formalism used for construction of spinning particles in [24][25][26][27], and gives precise mathematical formulation of the oldest idea about spin as the "inner angular momentum".