- Acute (less than 7 days), sub-acute (7 days to 7 weeks), or chronic (more than 7 weeks) LBP matching classifications 1, 2, or 3 of the Quebec Task Force (QTF) Classification system - QTF 1: Pain without radiation, QTF 2: Pain + radiation to proximal extremity, QTF 3: Pain + radiation to distal extremity, QTF 7: Spinal stenosis