The only vaulters who I have seen who jumped 'like Bubka before Bubka' were folk like Warmerdam whose technique was conceptually the same, and Slusarski of Poland, the 1976 Olympic Champion, who demonstrated perhaps the most critical of the Petrov/Bubka characteristics - an unloaded pole at take off.
So I would really appreciate it if someone could post film of US vaulters - or anyone other than Slusarski - who jumped 'like' Bubka before 1980 - i.e. before Bubka!

