WordNet sense 1 (in or of a state of physical or nervous tension):

tense

WordNet sense 2 (lacking natural ease):

labored, laboured

WordNet sense 3 (lacking grace or skill in manner or movement or performance):

awkward

WordNet sense 4 (lacking spontaneity; not natural):

constrained, forced

WordNet sense 5 (struggling for effect):

agonistic

WordNet sense 6 (speaking or behaving in an artificial way to make an impression):

affected, unnatural