but getting nowhere
This poem is specifically about a person trying to lose weight by walking on a treadmill. Over time, the person walks many miles but loses no weight. The “getting nowhere” part refers to the person not achieving what they desired, but also to the idea that they are in the same place while walking on the machine. The idea was to use the phrase symbolically and literally.
More generally, the poem is about effort without result and could be symbolic of many experiences.