In pictures: US candidates' body language

She says Mr Romney benefits in terms of likeability from being handsome, as well as from his height, a "power cue". History has shown the taller of the last two candidates in a presidential race usually wins.

Making a fist is another power cue, a masculine gesture designed to show the candidate is tough.

Ms Wood says President George W Bush began using this power cue more during his 2000 election campaign, when critics questioned his military service in the Vietnam War.