That's a bit slow
Måske "han" er et lille barn.
In (UK) English we would more often say: he runs AT one metre per second. This should be an acceptable translation.
Why is he saying SEKUNDS?
It is actually not an S in the end but an aspiration (in English one has it in words "t_ea", "p_ark", "k_een" and many, many others.
at one metre a second