grueling

 gruel·ing

[ˈɡro͞oəliNG]

ADJECTIVE

1. extremely tiring and demanding:

   "a grueling schedule"
2. Dr Fredrick mentioned in the article that " After studying medicine and then doing a grueling residency and fellowship training for a total of ten years before even starting to see patients independently, it can be hard to say “I don’t know” when faced with certain questions".