effortful

from WordNet (r) 3.0 (2006)

effortful
    adj 1: requiring great physical effort [ant: {effortless}]

from The Collaborative International Dictionary of English v.0.48

effortful \effortful\ adj.
   1. requiring great physical effort. Opposite of {effortless}.
      [Narrower terms: {arduous, backbreaking, back-breaking,
      grueling, gruelling, hard, heavy, laborious, labourious,
      punishing, slavish, strenuous, toilsome}; {exhausting,
      tiring, wearing, wearying}] Also See: {difficult}, {hard}.
      [WordNet 1.5]