This is 1958 (via Wikipedia):
This is 1964 (via Getty):
This is 1968 (via Getty):
High jump has always iterated in style but prior to 1968 each iteration was limited by the landing. When participants landed in sand they landed on their feet. As the pit changed from sand to wood chips to foam the form changed with it.
Normally we focus on the stakeholders and reducing the restricted action section. Sometimes limits are malleable but sometimes they have to be structural changes. Technology, even just foam, is an external change that might mean this time is different.