burdensome

Synonyms: These adjectives apply to what imposes a severe test of bodily or spiritual strength. Burdensome is associated with both mental and physical hardship: The burdensome task of preparing her tax return awaited her.
Onerous connotes the figuratively heavy load imposed by something irksome or annoying: My only onerous duty was having to greet the guests.
Something oppressive weighs one down in body or spirit: "Old forms of government finally grow so oppressive that they must be thrown off" (Herbert Spencer).
Arduous emphasizes the expenditure of sustained and often exhausting labor: Becoming a doctor is an arduous undertaking.
Demanding, rigorous, and exacting imply the imposition of severe and uncompromising demands: Music is a demanding art. "Yet out of this unflattering, rigorous realism . . . Swift made great art" (M.D. Aeschliman). Archaeology is exacting work.