National's Alfred Ngaro has posted a video pretending to outlift Labour's Stuart Nash, using tiny weights.

It follows Mr Nash, a Minister of the Crown, posting a video on Tuesday evening of himself lifting weights in the Parliamentary gym.

He said he did five sets of 12 reps with 45kg dumbbells, subtly pointing out that there were no heavier weights available in the gym.

"Not bad for an old geezer," he said.

The video was filmed at 11pm in between reading papers, Mr Nash said on the video posted to his Facebook page.