Here's a 1981 ad for some old school Mizuno running shoes featuring the RB midsole which supposedly had a longer life span. According to this ad "Laboratory tests show that it retains its strength and resiliency when other materials have lost theirs."
Ad info is below:
There are two ways to pick a running shoe: With your feet, or with your head.
Your feet can tell you a lot about a running shoe. But if you're a serious runner, you need to know more. You need to know how well a shoe protects you from injury. You need to know how well it will stand up to your running program. And you need to know how it will feel once you start running in it.
That's why you also need to use your head. And that's why Mizuno has created a line of running shoes unlike any other in the world. Mizuno is one of the world's leading manufacturers of baseball, volleyball, and all-purpose athletic shoes. This experience has helped us develop uniquely durable materials and incorporate them into a new line of technologically advanced running shoes.
In the store they'll impress you. Down the road they'll amaze you. For example, only Mizuno shoes have the exclusive RB* midsole. Laboratory tests show that it retains its strength and resiliency when other materials have lost theirs. So the shock absorption you feel when you first run in a pair of Mizunos stays with you after other shoes have gone flat. Mizuno has specially designed features to protect you from injury. Like an extended medial heel counter of extra-firm leather board material. A removable conformal footbed cup insole. And a carbon black compounded rubber outsole.
In addition, an 8° last design in the sole guides your foot to its most natural position each time it lands. The result is a shoe with lightweight flexibility, exceptional fit, outstanding cushioning, and protection from the kinds of injuries that can be caused by improper shoe design. One other reason to use your head when buying running shoes is price. While Mizuno shoes are not inexpensive, they are priced to compete with shoes that we believe offer you far less. We hope we convinced you that Mizuno is an outstanding new running shoe. And if so, we hope you'll see your Mizuno dealer—and let us convince your feet.
Marketed and Distributed exclusively by Curley-Bates Co., 860 Stanton Road, Burlingante, CA 94010 • (415) 697-6420 .
*RB sole not available in beginner model MZ TR-50
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The Exclusive RB Midsole
After equal wear, cells of the RB midsole stand up far better than cells of the less expensive EVA midsoles which are used by many leading manufacturers.
The Impact Life of a Running Shoe / Impact Force Resiliency
While the average training shoe has a "prime" life of about 350 miles, you can expect that Mizuno shoes will retain their superior impact characteristics and give you many more miles of wear. Quality you would expect from Mizuno, one of the world's leading suppliers of athletic footwear