Although Eratosthenes FGrH 241 fr. 8J writes that Astyanax won the periodos six times (Ἀ[ϲτ]υάναξ ὁ Μιλήϲιοϲ ϛ τὴν περίοδον ἀκονιτεί), Moretti (1957, no. 479) argues that this is impossible, as such a successful career length is highly implausible, because the dates of the presumed victories are in contradiction with other known victories at the periodos, and because the athlete is probably known from another source (Athenaeus) in which it is said he won the periodos three times.
Moretti discusses several possible interpretations and concludes that it is most likely that Astyanax was the sixth person to win the periodos ἀκονιτί (litt. 'without dust', i.e. 'effortless' acc. to LSJ) - CT