text: Richard Parks had been attempting to become the first person to take blood and muscle samples at the summit to investigate the effects of altitude.
  But Parks, 38, who was climbing without using supplemental oxygen, has returned to Wales after becoming at "high risk of life-threatening complications".
  He has previously climbed Everest and trekked solo to the South Pole.
  The former Wales rugby international, originally from Pontypridd, had reached Camp Two, which is 6,400m (21,000ft) above sea level - the summit is 8,848m (29,029ft).
  But he ended the expedition after results over the weekend showed he had abnormal blood readings, putting him at greater risk of a stroke or heart attack.
  The climb had been 18 months in the planning and was part of the collaborative British research expedition called Project Everest Cynllun.
  It was hoped data from the project would allow researchers to explore the mechanisms underpinning dementia and resilience.
  On ending the world-first bid, Parks said it had "been a bitter pill to swallow".
  "I am confident of my process to make the decision. It's the right one. I'm at peace, but it's been a brutal few days," he said.
  "I am not prepared to risk my life over and above the risks I have considered, trained and prepared for, or risk the lives of those around me."
  Parks was a back-row forward who played for Pontypridd, Leeds, Perpignan and Newport Gwent Dragons and won four caps for Wales.
target: A Welsh adventurer has been forced to end his expedition on Mount Everest due to "medical complications".