Clue: Long-distance runner, not fully fresh as of old (5)
Answer: VIREN
Explanation: Long-distance runner, not fully fresh as of old (5)
VIRENT (verdant, fresh) truncated; the runner is Lasse Virén, who won gold medals in the 5000m and 10000m at the 1972 and 1976 Olympics. Again I misguessed here, and spent ages trying to justify SIREN.