Read the trial, pain DID reduce across the entire study function...

Read the trial, pain DID reduce across the entire study function was increased with those who reported LBP Within 5 years, those who reported LBP for more than 5 years showed no improvement in function but showed significant reduction in pain.

if you've been living with LBP for more than 5 years it's reasonable to assume you won't have complete or improved function, but pain is manageable, almost as if your body has grown accustomed to the reduced function, study shows less than 5 years it's the sweet spot.

which is why it specifies "across the entire study"' as they have recruited people of varying degrees of LBP