Reciprocating fluid pumps include a reinforced shaft including an inner shaft and a protective cover. The protective cover at least substantially encapsulates the inner shaft. The inner shaft exhibits a greater resistance to mechanical deformation than the protective cover, and the protective cover exhibits a greater resistance to chemical corrosion by the subject fluid than the inner shaft. Methods of forming a reciprocating fluid pump include forming a reinforced shaft and positioning the reinforced shaft within a subject fluid chamber and between two plungers.