IAAF changes testosterone rules

The rules, which start on 1 November 2018, would apply to women who race in track events from 400m up to the mile.

The IAAF believes the new measures will stop women with high testosterone levels gaining a competitive advantage.

Olympic 800m champion Caster Semenya is expected to be among those affected.

The South African runner has previously been asked to undertake gender testing by athletics chiefs but no results have ever officially been made public.

Russian athletes told to prove they are clean

The warning comes as part of new guidelines issued by the IAAF, which has set out the criteria athletes must meet in order to compete as neutrals. 

Russia has been banned from IAAF competition since 2015 following allegations of state-sponsored doping.

The recent McLaren report claimed more than 1,000 Russians benefited from a doping programme in the country between 2011 and 2015.