Measure the anterior deltoid and the latissimus dorsi, and take both sides every time. Research using a handheld myotonometer in adhesive capsulitis patients found both muscles were significantly stiffer on the affected side. The pectoralis major was not. That pattern tells you where to put the probe.
Which Muscles Show a Measurable Difference?
The anterior deltoid and the latissimus dorsi. A study in JSES International measured muscle stiffness in 40 adhesive capsulitis patients with a handheld myotonometer, comparing the affected shoulder against the unaffected one in the same patient. Anterior deltoid stiffness was significantly higher on the affected side. Latissimus dorsi followed the same pattern. Pectoralis major did not differ significantly between sides. That is a useful negative result: it saves you a measurement point that will not tell you anything.
Why Measure Both Shoulders?
Because the within-patient comparison is the only one you can trust. Absolute stiffness values vary widely between individuals, and published normative data is still thin. A 2025 paper in the Journal of Manual and Manipulative Therapy reporting reference values for stiffness and asymmetry makes the same point: asymmetry is often more interpretable than a raw number. In a unilateral condition like frozen shoulder, you have a built-in control arm attached to the same patient. Use it.
| Measurement site | Evidence of side-to-side difference | Worth including? |
|---|---|---|
| Anterior deltoid | Significantly stiffer on the affected side | Yes. Primary site |
| Latissimus dorsi | Significantly stiffer on the affected side | Yes. Secondary site |
| Pectoralis major | No significant difference reported | Optional. Low yield |
| Upper trapezius | Not isolated in this study | Optional. Track if guarding is obvious |
| Glenohumeral capsule | Not reachable by surface measurement | No. Use range of motion or imaging |
Does the Reading Diagnose Frozen Shoulder?
No, and it should not be presented that way. Adhesive capsulitis is diagnosed clinically, from history and a capsular pattern of restriction, with imaging where indicated. What a stiffness reading may reflect is secondary muscular change around a joint the patient has stopped moving. That is worth tracking through rehabilitation, but the number is a monitoring tool, not a diagnostic one. The capsular restriction that defines the condition sits deeper than any surface device can read.
How Reliable Is a Handheld Device at the Shoulder?
Good for superficial muscle, with the usual caveats about depth. The JSES International work reported a very high correlation between handheld myotonometry and shear wave elastography on the same tissue. A 2024 reliability study of the MyotonPRO placed intra-rater and inter-rater agreement in the good to excellent range across measured muscles. The limitation is consistent across the literature: surface measurement reads what is under the probe, so deeper structures and heavier soft tissue coverage reduce what you can interpret.
Survey data: In a 2026 survey of 455 patients who stopped chiropractic care, 58% cited perception-based reasons: 36% felt no progress, and 22% felt better and stopped. Neither group was told their stiffness was still elevated.
Why Does This Matter Through a Long Rehabilitation?
Because frozen shoulder takes months, and pain is a poor guide across that timeline. The condition moves through phases, and a patient whose pain settles before their motion returns will reasonably conclude they are finished. A second channel of measured data, taken at the same points on both sides every four to six weeks, gives you something to put in front of them that is independent of how the shoulder felt that morning. Set the expectation early that stiffness, pain, and range of motion may move at different rates, because they often do.
Frequently Asked Questions
Which muscles should you measure in a frozen shoulder patient?
Start with the anterior deltoid and the latissimus dorsi, measured on both sides. A study in JSES International using a handheld myotonometer found both were significantly stiffer on the affected side in adhesive capsulitis patients, while the pectoralis major showed no significant side-to-side difference.
Why measure the unaffected shoulder too?
Because absolute stiffness values vary widely between people. The unaffected side gives you a within-patient comparison, which is more informative than comparing one patient against a population average. The adhesive capsulitis research is built on exactly this side-to-side design.
Does muscle stiffness diagnose frozen shoulder?
No. Adhesive capsulitis is a clinical diagnosis based on history, capsular pattern restriction, and imaging where indicated. A stiffness reading may reflect secondary muscular changes around the joint, but it is a tracking measure, not a diagnostic test.
Is a handheld myotonometer accurate enough for shoulder work?
For superficial muscles, the agreement with imaging is strong. The JSES International study reported a very high correlation between handheld myotonometry and shear wave elastography readings. Reliability studies of the MyotonPRO have generally placed intra-rater and inter-rater agreement in the good to excellent range.
Can you measure the joint capsule itself?
No, not with surface measurement. A handheld device reads the tissue directly under the probe, which for the shoulder means superficial muscle. The capsular restriction that defines frozen shoulder sits deeper and requires imaging or clinical range-of-motion testing instead.
How often should you re-measure during frozen shoulder rehabilitation?
At the same interval as your other re-examination measures, commonly every four to six weeks. Frozen shoulder moves through phases over months, so measuring too frequently produces noise rather than a trend.
What should you tell the patient about the numbers?
That the reading tracks the muscles around the joint, not the joint capsule, and that it may change at a different rate than pain or range of motion. Setting that expectation early avoids confusion when the three measures move independently.
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.