Leaders Debate: Decoding the body language

More than a million people watched the Newshub Leaders Debate on Monday night, but there was more to it than just what was said.

National's Bill English and Labour's Jacinda Ardern faced off for a fiery hour and 20 minutes, broadcast on TV, Facebook, YouTube and the Newshub website.

Rather than just what they said, it's how they said it which has captivated viewers - around 90 percent of communication is non-verbal, experts say.

From eye rolls to nervous smiles to hand gestures, body language can betray the words coming out of your mouth.

So how did the leaders stack up in the debate? Three's The Project asked body language specialist Suzanne Masefield for the good, the bad and the ugly.

When it came to Ms Ardern's steadfast declaration she had never lied in politics, Ms Masefield agreed her body language lined up, describing her as "very earnest".

"Everything matches with that, it's very earnest and very sincere. It's very connecting for people," she said.

Mr English's comments on rebuilding the economy after the recession was praised as being "the most emotional part in the debate for him", Ms Masefield said.

But not everything was sunshine when it came to posture.

Watch the video for The Project's full report.