gruelling

/G R UW1 L IH0 NG/
noun
  1. 1

    (racing) A race in which the animal being raced finishes in a state of physical exhaustion.

  2. 2

    A gruelling ordeal.

adjective
  1. 1

    So difficult or taxing as to make one exhausted; backbreaking.

Source: https://en.wiktionary.org/wiki/gruelling