1) Arduous 2) Backbreaking 3) Difficult 4) Dragging 5) Exhausting 6) Grueling 7) Gruelling 8) Hard 9) Heavy 10) Labor-intensive 11) Labored 12) Laborious 13) Labour-intensive 14) Laboured 15) Leaden 16) Marked by effort or exertion 17) Plodding 18) Punishing 19) Sisyphean 20) Straining 21) Strenuous 1) Arduous 2) Difficult 3) Dragging 4) Grueling 5) Gruelling 6) Hard 7) Laborious 8) Plodding 9) Punishing 10) Straining 11) Tiring 12) Toilsome 13) Wearing 14) Wearying 
[adj] - requiring great physical effort
adjective requiring great physical effort
marked by effort or exertion; labored.