Directional Preference: What's Happening in the Tissue?
By: Embodia Team ∙ Estimated reading time: 8 minutes

MDT Is a Pattern, Not a Diagnosis

If you've spent time with McKenzie Method / Mechanical Diagnosis and Therapy (MDT), you already know how to find a directional preference (DP). You repeat or sustain an end-range movement and watch for centralization, reduced pain, or restored range. But a question that comes up constantly among practitioners working through this material is a different one: what's actually happening at the tissue level when that happens?

This question came up recently from a practitioner working through the course, Managing Mechanical LBP and PGP – Telerehabilitation Friendly with Carolyn Vandyken, BHSc (PT), CredMDT, CCMA. It's a fair question to sit with, because the honest answer is more nuanced than a single mechanism.

The Short Answer: Nobody has Fully Nailed it Down

MDT is a clinical classification system, not a tissue diagnosis. You're not identifying a structure. You're identifying a reproducible behavioral pattern: symptoms that centralize, reduce, or abolish with a specific direction of repeated or sustained movement, and worsen or peripheralize with the opposite direction. That pattern is clinically useful and well-documented. 

The original theory: disc mechanics.

Robin McKenzie's early explanation centered on the intervertebral disc. The idea that repeated end-range loading could shift nucleus pulposus material within the disc, and that this shift explained why symptoms would centralize in one direction and peripheralize in the other. It's an intuitive model, and it's still the explanation many clinicians learned first.

Why that explanation has lost ground.

The tighter the research has looked at correlating imaging findings (disc bulges, degeneration, annular changes) with directional preference and pain behavior, the weaker that correlation has turned out to be. Asymptomatic disc pathology is extremely common, DP and centralization show up in patients without notable discogenic findings on imaging, and the rate at which symptoms centralize (sometimes within a single assessment session) is hard to explain purely through slow mechanical fluid shifts within a disc. This is consistent with what your course material touches on: for the large majority of low back pain presentations, no single structural cause is identifiable, which is a big part of why the field describes most LBP as "non-specific."

So What are the More Current Explanations?

None of these are settled science, and MDT researchers themselves are careful not to overclaim here, but a few mechanisms show up regularly in discussion of why repeated/sustained end-range movement changes pain:

• Mechanical loading of pain-sensitive structures beyond the disc. Facet joints, ligaments, and the posterior annulus are all richly innervated, and directional loading changes the strain and compressive load on these structures, not just the disc.
  
  
• Neurophysiological modulation. Repeated movement into a specific direction may influence nociceptive signaling through mechanisms similar to those seen with graded movement and exposure more broadly, altering the sensitivity of the system rather than "fixing" a structure.
  
  
• Motor control and movement pattern changes. Patients often move differently once given a clear, specific movement strategy, which can change loading patterns throughout the session and beyond.
  
  
• Central and psychosocial contributors. Giving a patient an active, self-directed strategy that reliably changes their symptoms, in real time, in front of them, builds self-efficacy and a sense of control. That's not "just" psychological; there's a reasonable argument that this contributes to the outcome alongside whatever is happening mechanically.

The summary: DP and centralization are a reliable, reproducible clinical phenomenon with strong outcome data behind them. The precise combination of tissue-level, neurophysiological, and psychosocial mechanisms that produce that phenomenon is still an open question, and that's true of most mechanical low back pain, not just the MDT model.

What the Evidence Does Support Clearly

Even without a fully resolved tissue-level explanation, the outcome evidence for using DP to guide treatment is worth knowing well.

Long, Donelson & Fung (2004), Spine: a multicentered RCT of 312 LBP patients. This is one of the studies most often cited here. In it, 74% of patients demonstrated a directional preference on standardized mechanical assessment. Those patients were randomized to exercises matching their DP, exercises in the opposite direction, or non-directional "evidence-based care" (general mobility and strengthening). At two weeks:

• The matched-direction group showed significantly greater improvement than both other groups across every outcome measured: pain, disability (Roland-Morris), medication use, and activity interference.
  
  
• On self-rated outcome, 44.4% of the matched group reported their back problem had fully resolved and another 50% reported improvement — a combined 94.4% reporting resolved-or-improved, compared with about 25% in the opposite-direction group and 44% in the evidence-based-care group.
  
  
• Not a single subject in the matched-direction group reported worsening symptoms or symptoms spreading further into the leg. Both other groups did.

Namnaqani et al. (2019), Journal of Musculoskeletal and Neuronal Interactions: a systematic review of five RCTs comparing MDT to manual therapy for chronic LBP. This study found that MDT produced greater short-term pain reduction (2–3 months) across all five included trials, and better long-term disability outcomes (6–12 months) in most of them, compared to manual therapy. The review is upfront about its limits: patient and therapist blinding isn't achievable in this kind of trial, a few of the included studies were small, and the authors note the evidence base, while consistent, isn't yet large or high-powered enough to be the final word.

The Practical Takeaway

You don't need a fully resolved tissue-level mechanism to use directional preference well. The clinical reasoning and outcome data stand on their own. But it's worth being precise with patients (and with yourself) about what you actually know: DP identifies a pattern that predicts who responds to what, not a confirmed structural diagnosis. Communicating it that way: "we've found a movement direction that reliably changes your symptoms, and we're going to build your program around that"  tends to land better than reaching for a specific tissue explanation you can't fully back up.

If you want to go deeper into the classification system itself, including leg-dominant vs. back-dominant pain, repeated test movements, and how to build a program around what you find, that's exactly what the Directional Preference Matters module inside Managing Mechanical LBP and PGP – Telerehabilitation Friendly walks through.

MDT Exercises on Embodia

Once you've identified a patient's directional preference, you need a way to actually prescribe it. Embodia's exercise library includes a range of MDT-aligned exercises, including content from Carolyn Vandyken herself, ready to build directly into a home exercise program alongside your own instructions on reps, sets, and hold times.

Carolyn's Managing Mechanical LBP and PGP course includes 17 exercises and 1 patient education resource as part of its own resource package, available to browse from the course's exercises tab. Plus, Embodia has a complete MDT library available to all Tier 2 and 3 Members.

Here's a sample from the library

Related Learning

• Embodia's home exercise program library: learn more about prescribing exercises on Embodia, including MDT-aligned content
  
  
• The McKenzie Method: Clearing Up the Misconceptions: a deeper look at what MDT actually is (and isn't), including the same point this post makes about the disc model being one useful explanation rather than the whole story
  
  
• Managing Mechanical LBP and PGP – Telerehabilitation Friendly with Carolyn Vandyken
  
  
• Browse all of Carolyn Vandyken's courses on Embodia: for practitioners who want to go further into her work across orthopaedics and pelvic health

References

Long A, Donelson R, Fung T. Does it matter which exercise? A randomized control trial of exercise for low back pain. Spine. 2004;29(23):2593–2602.

Namnaqani FI, Mashabi AS, Yaseen KM, Alshehri MA. The effectiveness of McKenzie method compared to manual therapy for treating chronic low back pain: a systematic review. J Musculoskelet Neuronal Interact. 2019;19(4):492–499.*