Latest: Cyclist Chris Froome needs scientific proof for spike of asthma drug in system

Update 4.35pm: Chris Froome's defence against a doping ban will hinge on his ability to prove there is a scientific reason for the spike in his Salbutamol readings at La Vuelta, experts have said.

The 32-year-old rider has been asked to explain why a urine sample he gave during September's race in Spain contained twice the permitted concentration of the widely-used asthma drug.