needing and using much energy and thought

difficult, hard to endure

heavy and awkward to carry

clumsy, awkward

requiring much effort, strength, skill or ability

hard on someone; hard to do

needing a lot of (mental or physical) effort

demanding

having (a lot of) weight; difficult to carry or move; of more than usual size, amount etc

having great weight

needing, showing, great effort

hard, difficult

needing much effort

difficult; requiring hard labor

slow and heavy; (of written style) serious and dull

heavy, cumbersome

careful and determined; harsh; severe

severe; exact

annoying

irritating, exasperating

causing worry, unhappiness, difficulty

bothersome, worrisome

awkward to move or control because of shape, size or weight

awkward, bulky

(moving) in the opposite direction to the stream or current

hard on someone; hard to do

very heavy; having strong influence

heavy

causing worry

troublesome