Mckenzie method (or Mechanical Diagnosis and Therapy, MDT) is a system to both diagnose and treat musculoskeletal disorders. With Mckenzie, the pain is categorized into four classifications - posture syndrome, dysfunction syndrome, derangement syndrome, and non-mechanical syndrome. These classifications will determine what treatment type to use. 

The most common classification is derangement syndrome. This includes sciatica, pinched nerve, numbness and tingling into your arms and legs, disc herniations, etc. When these conditions present, the doctor will work with you to discover your directional preference. This is a specific direction identified by the patients body, that when done repeatedly, can help decrease pain or centralize the pain. Centralization is the process of the pain closer to the spine, which is typically the source of the pain. This is the key to confirming the directional preference. However, if the repeated loading does the opposite -  aka peripheralization (pain moving towards the periphery or further from the spine), then we can conclude that the direction is not the patient's directional preference.

Once your directional preference is determined, it is repeated several times at end-range loading. This means as much range of motion in that direction as the patient can at the moment. As they move through repeated, end-range loading, the inflammation or pressure that is hitting the affected nerve root will decrease, resulting in less numbness, tingling, burning, and pain.