Olympic champion Jessica Ennis-Hill leads after four events in her first heptathlon since winning gold in last year's World Championships.
Former world and Olympic champion Christine Ohuruogu withdraws from the British Championships - also the Olympic trials - with a virus.
Rio's anti-doping Laboratory is suspended by Wada just six weeks before the Brazilian city hosts the Olympic Games.
Olympic champion Greg Rutherford pulls out of this weekend's British Championships in Birmingham because of fitness concerns.
Audio & Video
BBC Sport counts down to the 2016 Rio Olympics with the moment Ethiopian barefoot long-distance runner Abebe Bikila won the 1960 marathon.
How to get into Athletics
How to get into athletics - one of the widest ranges of choice in sport, from jumps and throws to sprints or distance running.
What's on BBC Sport this week
This week's sport on the BBC includes Euro 2016, England v Sri Lanka ODIs, tennis from Eastbourne and the British Athletics Championships.