Nike's controversial Vaporfly shoes make runners faster — so runners sponsored by other brands are blacking them out to wear in secret

· Nike's Vaporfly shoes have been involved in nearly every major running victory and milestone since 2016.
· Research suggests the Vaporfly soles give runners more energetic efficiency: at least a 4% boost over shoes from competing brands.
· Vaporflys are so advantageous that some runners sponsored by other brands have taken...