The shoes came in the colors of a tropical drink, lime and orange and pink, as if the logo ought to be an umbrella instead of a Nike swoosh. You half expected the insoles to smell of rum and coconut.

If the color scheme suggested frivolity, race results did not. The shoes cushioned the feet of all three medalists in the men’s marathon at the Rio Olympics last summer. Later, in the fall, they were worn by the winners of major marathons in Berlin, Chicago and New York.

The latest shoe designs have produced fast times and impressive results in international races. But they have also spurred yet another debate about the advance of technology and the gray area where innovation meets extremely vague rules about what is considered unfair performance enhancement for the feet.

Where to draw the line of permissible assistance?

Many sports have struggled with the answer. Swimming allowed record-setting, full-body suits, then banned them after the 2008 Beijing Olympics because they gave an unfair advantage in buoyancy and speed. And track and field wrestled with the issue of prosthetic blades worn by the South African sprinter Oscar Pistorius.