A change counts once it exceeds the minimal detectable change for that muscle and device. That threshold is the amount a reading can drift from measurement noise alone. Any difference smaller than it may reflect nothing real in the tissue. Knowing the number keeps you from calling ordinary variation "progress" in front of a patient.
What is minimal detectable change?
It is the smallest difference between two readings that is unlikely to be error. Every measurement tool has some built-in wobble, so two readings of an unchanged muscle will rarely be identical. Minimal detectable change, often written as MDC, is calculated from the tool's reliability and typical variability. It marks the line below which a difference could just be noise and above which you can reasonably call the change real.
A 2022 study in Scientific Reports laid out a protocol and reference values for the minimal detectable change of muscle and tendon stiffness measured with a handheld device, giving clinicians muscle-specific thresholds rather than one blanket number.
How consistent are the readings in the first place?
Consistent enough that small real changes are detectable. A 2024 systematic review of 48 studies covering 31 muscle groups reported a typical coefficient of variation for stiffness at or below 5.2%, with intra-rater reliability frequently above 0.90. The tighter the variability, the smaller the change you can trust, which is why a repeatable tool matters as much as the reading it produces.
Why is the threshold different for each muscle?
Because tissue depth, resting tone, and baseline variability differ from muscle to muscle. A large superficial muscle sits closer to the sensor and behaves differently than a smaller or deeper one. That means the minimal detectable change is muscle-specific, and a difference that is meaningful in one site may be noise in another. Applying a single threshold everywhere will mislead you.
| Reading scenario | Difference vs baseline | Interpretation |
|---|---|---|
| Below minimal detectable change | Small | May be measurement noise, not real |
| At or above minimal detectable change | Larger | Likely a real change in the tissue |
| Within coefficient of variation | Very small | Expected wobble on repeat readings |
How do you use this with a patient?
Measure a baseline, re-measure later, and check whether the difference clears the minimal detectable change for that muscle. If it does, you can tell the patient the change is real and show them the number. If it does not, you hold off rather than dress up noise as improvement. That discipline is what makes an objective reading more trustworthy than a subjective impression, and it protects your credibility over a course of care.
Survey data: In a 2026 survey of 455 patients who stopped chiropractic care early, 58% cited perception-based reasons: 36% felt no progress, and 22% felt better and self-discharged. A reading that clears the meaningful-change threshold gives the no-progress group evidence they can see, and gives the felt-better group a reason to finish care.
Should you compare to reference values instead?
Reference values give rough context, but within-patient change is the stronger tool. Population ranges for stiffness are wide, so a single reading against them says less than a tracked change from a patient's own baseline. Watch the patient against themselves, and use the minimal detectable change as your bar for what counts.
Frequently Asked Questions
How much does a stiffness reading need to change to be meaningful?
Enough to exceed the minimal detectable change for that muscle and device. That threshold is the amount a reading can move from noise alone. Below it, a difference may not reflect any real tissue change.
What is minimal detectable change?
It is the smallest difference between two readings that is unlikely to be measurement error. It is calculated from the tool's reliability and variability, and it sets the floor for calling a change real.
How consistent are myotonometry stiffness readings?
A 2024 systematic review reported a typical coefficient of variation for stiffness at or below 5.2%, with intra-rater reliability frequently above 0.90. That consistency is what makes small but real changes detectable.
Why does the threshold differ between muscles?
Each muscle has its own depth, resting tone, and baseline variability, so the minimal detectable change is muscle-specific. A large superficial muscle does not share the same threshold as a small or deeper one.
How do I use this with a patient?
Compare a re-measurement to the patient's own baseline and check whether the difference clears the minimal detectable change. If it does, the change is real. If it does not, you avoid overselling noise as progress.
Can I compare a patient's reading to normal reference values?
You can use them as rough context, but within-patient change from a personal baseline is more useful. Reference ranges are wide, so a single reading against them says less than a tracked change over time.
Citations
- Protocol and reference values for minimal detectable change of muscle and tendon stiffness (2022). Scientific Reports.
https://www.nature.com/articles/s41598-022-17507-2 - Evaluating the Reliability of MyotonPro in Assessing Muscle Properties: A Systematic Review of Diagnostic Test Accuracy (2024). PubMed PMID 38929468.
https://pubmed.ncbi.nlm.nih.gov/38929468/ - The Utility of Myotonometry in Musculoskeletal Rehabilitation and Human Performance Programming (2023). Journal of Athletic Training. PubMed PMID 37418563.
https://pubmed.ncbi.nlm.nih.gov/37418563/
One approach is to add a second channel of objective data alongside subjective pain reports. Options include soft tissue stiffness measurement (such as MuscleMap), range-of-motion testing, and posture analysis. Each gives you something concrete to show the patient rather than asking them to take your word for it.