What is grueling?

Some articles on grueling:

WWE Tough Enough - Revival (Season 5) - Episodes
2011 3 Bill sends the contestants on a grueling run ... Bill puts her through a grueling workout ... The contestants also undergo a grueling outdoor obstacle course, which shows the lack of endurance some have ...
Michael Hossack
... After a grueling stint in upstate New York, the band relocated to the San Francisco bay area and signed with a production company that had also signed the newly ... After a grueling ten-month tour in 1973, Hossack left the Doobies ... After months of healing and grueling physical therapy, Mike was back with the band ...