Possible meanings are 1) "strong legs" is a metonym that represents how swiftly a man can run. Alternate translation: "men who can run swiftly" or 2) "strong legs" represents the strength of the whole man. Alternate translation: "how strong a man is" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-synecdoche]])