The speaker feels trapped in a cycle of endless effort. Life is pictured as a circle they keep walking, lap after lap, getting nowhere new. The walking is tiring and painful: the body gasps and overheats, and the speaker says nobody sees this suffering or even gives it a name. Each lap wears them down, yet a stubborn inner strength, "clenched power," keeps them going.
The mood is weary and bitter at first. There is a quiet frustration in the line about growing old without growing wise, as if experience has brought exhaustion rather than insight. The ending shifts the tone. Breaking the circle seems to mean death, and only then, the speaker suggests, will others understand that nothing was in vain. It's a hopeful note, but a sad one too, since the meaning arrives only when the struggle is over.