A three-point bending test under quasi-static load conditions is usually used in studies on the bones' mechanical properties. On its basis, the bone strength is determined, corresponding to the maximum force required for the fracture. In natural conditions, bone fractures most often occur as a result of an impact or fall, i.e. under dynamic loads, when a large force acts on the bone in a concise time. This work presents the results of a dynamic two-point bending test of rat bones. Two groups of the humerus were analyzed: healthy (as a control) and ovariectomized rats (as an osteoporosis model). During the bending test in the analyzed bone cross-section, a complex state of the surface density of internal forces appeared, characterized by the simultaneous occurrence of normal and tangential stresses. The obtained results determined the influence of osteoporotic changes on the transmitted dynamic forces values. The values of tensile and compressive stresses occurring at bone fracture were dependent rather on the bone asymmetry, the moment of inertia of its cross-section, and material properties than the loading force.