All this is from memory, so please correct me if I misstate something...
Lendl was an early adopter of composite frames among the pros. He rose to prominence with the Kneissl White Star Pro, even then considered barely a mid at about 77 sq. in. He signed in the early 80's with Adidas, who used the Kneissl mold to make the GTX Pro, basically the same racket except foam-filled and painted silver and blue.
Toward the end of his career he signed a golden parachute of a contract with Mizuno, who – again – made for him more or less the same racket, this time painted gold, black, and red. During this period he experimented with some true midsize frames provided by Mizuno, but I don't know if he used them in competition.
Something you don't hear noted often about Lendl is that he played well into the 90's near the top of the game using what was essentially a standard-size racket, many years after everyone else had gone to mid, midplus, and oversize frames.
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