Convicted dope cheats such as sprinter Justin Gatlin could still be benefiting from having taken banned substances long after their bans have expired.
Research by University of OsloÂ scientists has established that muscles can retain the advantages given by anabolic steroids decades after the point at which they were taken.
The data casts another shadow over once-banned athletes such as controversial US athlete Gatlin, Tyson Gay – the second fastest man in history – and Britain’s Dwain Chambers.
This summer, 32-year-old Gatlin ran the fastest ever 100m and 200m times by a man in his thirties despite twice having served suspensions.
The study has vast implications for the existing anti-doping system, where a first-time offender is unlikely to be suspended for more than two years and may well serve less than half that.
Kristian Gundersen, Professor of Physiology at the University of Oslo, who conducted the research in October 2013, told BBC Sport: “I think it is likely that effects could be lifelong or at least lasting decades in humans.
“Our data indicates the exclusion time of two years is far too short. Even four years is too short.”
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