British heptathlete Jessica Ennis-Hill has admitted that it is difficult to "comprehend" the number of athletes that are alleged to have committed doping offences.
A Germany television documentary has claimed that doping is rife within Russian sport, as well as alleging that as many as 150 suspicious blood samples weren't investigated between 2006 and 2008.
The 28-year-old told BBC Sport: "It's hard as an athlete to comprehend.
"It's an incredible amount of athletes, if true, and it's disappointing because we train incredibly hard to win medals. If you think about people cheating, it's really frustrating."
Ennis-Hill, who won gold in the heptathlon at the 2012 Olympics in London, has recently returned to training after giving birth in July.
