Fritz Lang was a perfectionist and the film was considered state-of-the-art regarding special effects. I have so far found nothing about that particular scene, but did find a few thing sthat could have worked.
From the Metropolis wikipedia article, I found this reference to a camera on a swing
Among the effects used are miniatures of the city, a camera on a swing, and most notably, the Schüfftan process, in which mirrors are used to create the illusion that actors are occupying miniature sets.
From this article on camera movement techniques, I found a reference to cranes and dollies being used in this time period.
However, cameramen eventually became more adventurous. Cranes and dollies were widely used by the 1920s, and the steadicam became a standard item by the 1960s
I haven't yet found a definitive answer. When I saw the reference to a sing, I thought the swing may have been used, since the scenes are short. But they last about 4 seconds and the camera movement is straight, not curved.
My original assumption, and what I strongly suspect was used, was a camera mounted on a crane being moved along a dolly track beside the runners. This could allow the camera to be above and in front of the runners, but the tracks would be out of frame to one side.
I will continue to look for something definitive and update the answer if I find it.