Anker: Shoulder Internal Rotation Strength Test – 0° Shoulder Abduction

The Shoulder Internal Rotation Strength Test measures the maximum isometric force produced during shoulder internal rotation with the shoulder positioned at 0° of abduction. Using the Anker, the assessment provides an objective and repeatable measure of internal rotator strength in a standardised position.

Internal rotation strength is essential for pushing movements, lifting, climbing, swimming, throwing acceleration and many activities of daily living. It also contributes to dynamic glenohumeral stability by helping maintain humeral head position during upper-limb movement.

The primary muscles assessed include the subscapularis, pectoralis major, latissimus dorsi, teres major and anterior deltoid.

When used with Measurz, the Anker records peak force and can calculate additional metrics including force relative to body weight, impulse, torque (when the lever arm is entered), rate of force development, time to peak and fatigue index.

The assessment measures muscle force only and should always be interpreted alongside symptoms, shoulder mobility and functional performance.

What Is the Shoulder Internal Rotation Strength Test?

The Shoulder Internal Rotation Strength Test is an isometric assessment where the client attempts to rotate the forearm towards the body while the elbow remains flexed to 90° and the upper arm stays against the trunk.

Testing with the shoulder at 0° abduction places the rotator cuff in a neutral position and provides a practical assessment of internal rotator strength without placing the shoulder in more demanding overhead positions.

The fixed resistance of the Anker allows repeatable testing when the same client position, anatomical landmarks and instructions are maintained.

Step-by-Step Protocol

1. Prepare the client

Explain that the assessment measures how strongly they can rotate their forearm towards their stomach without moving the elbow away from the body.

Record any:

• shoulder pain

• neck pain

• previous shoulder injury

• previous surgery

• neurological symptoms

• stiffness

• fatigue

Complete one or two familiarisation contractions before maximal testing.

2. Position the client

Position the client:

• seated upright

• feet flat on the floor

• trunk supported

• shoulder adducted against the side of the body

• elbow flexed to 90°

• forearm in neutral rotation

A towel may be placed between the arm and trunk to help maintain a consistent shoulder position throughout testing.

Maintain the same setup during every reassessment.

3. Position the testing limb

Ensure:

• the humerus remains against the trunk

• the elbow stays flexed to 90°

• the forearm begins in neutral

• the wrist remains relaxed

Position the Anker load cell against the volar (anterior) aspect of the distal forearm, approximately 3–5 cm proximal to the radial and ulnar styloid processes.

Avoid placing the load cell directly over the wrist joint.

Record the contact point to improve repeatability during future testing.

4. Stabilise the client

Prevent movement of:

• trunk

• shoulder girdle

• scapula

• elbow

The movement should occur only as an isometric shoulder internal rotation effort.

5. Testing instructions

Use consistent verbal cues.

"Rotate your forearm towards your body."

"Increase the pressure smoothly."

"Push as hard as you can."

"Hold."

"Keep breathing."

Repeat the same instructions during every reassessment.

6. Record the assessment

Use:

• 1–2 familiarisation trials

• 2–3 maximal trials

• 3–5 second contractions

• 30–60 seconds rest between trials

Record either:

• highest force value, or

• average of recorded trials

Maintain the same scoring method during future testing.

7. Repeat the trial if

• the elbow lifts away from the trunk

• the trunk rotates

• the shoulder elevates

• the forearm changes position

• the load cell slips

• pain limits maximal effort

• the client starts before instructed

Why It Is Used

The assessment may be useful for:

• baseline shoulder strength assessment

• side-to-side comparison

• monitoring strength over time

• athlete performance profiling

• objective reporting using Measurz

• monitoring response to exercise

• client education

The assessment should support broader clinical reasoning and should not be used as a stand-alone diagnostic or return-to-sport assessment.

What It Measures

The primary outcome is peak isometric shoulder internal rotation force.

When analysed in Measurz, additional metrics may include:

• Peak force

• Force relative to body weight

• Impulse

• Torque

• Rate of force development

• Time to peak

• Fatigue index

The assessment does not directly measure:

• rotator cuff integrity

• shoulder joint stability

• movement quality

• shoulder mobility

• throwing mechanics

• readiness for sport or work

Understanding the Result, Reference Values and What to Look For

Higher force values generally indicate greater shoulder internal rotation strength.

Lower force values may reflect:

• pain

• fatigue

• previous injury

• reduced confidence

• poor familiarisation

• inconsistent positioning

• movement compensation

Interpret results by considering:

• previous assessment results

• left versus right differences

• symptoms during testing

• movement compensations

• occupational, sporting or daily-life demands

Published Anker-specific normative values are currently unavailable.

Shoulder internal rotation strength has demonstrated excellent reliability using handheld and fixed dynamometry when shoulder position, elbow position and lever arm are standardised. Because testing protocols differ between devices, the client's own baseline and repeated assessments performed using the same setup are generally more meaningful than comparison with published force values.

A side-to-side difference of approximately 10% or greater may warrant further investigation, particularly when accompanied by symptoms, previous injury or reduced functional performance.

Assessing Different Client Populations

Youth

Interpret findings relative to growth, coordination and sporting participation.

Adults

Useful for baseline assessment and monitoring strength over time.

Older adults

Interpret alongside upper-limb function, lifting ability and activities of daily living.

Athletes

Particularly useful for throwing sports, swimming, racquet sports, combat sports and strength athletes.

Clients with persistent symptoms

Interpret alongside pain, confidence and functional capacity rather than muscle strength alone.

Common Errors and Limitations

Common errors include:

• elbow lifting away from the trunk

• shoulder abduction during the effort

• trunk rotation

• shoulder elevation

• inconsistent load cell placement

• inconsistent verbal cueing

Limitations include:

• results are specific to the testing position

• pain may reduce maximal force production

• muscle strength alone does not determine shoulder function

• published Anker-specific normative values remain limited

Practical Applications

The assessment may be useful for:

• establishing baseline shoulder strength

• monitoring progress over time

• comparing left and right limbs

• athlete performance profiling

• objective reporting using Measurz

• educating clients using measurable outcomes

FAQs

What does the Shoulder Internal Rotation Strength Test measure?

It measures maximal isometric shoulder internal rotation strength with the shoulder positioned at 0° abduction.

Why test with the shoulder at the side?

Testing at 0° shoulder abduction provides a comfortable and repeatable position while minimising unnecessary shoulder loading.

Which metric should be used routinely?

Peak force is the primary outcome measure.

Should both shoulders be tested?

Yes. Bilateral testing allows meaningful side-to-side comparison.

Can this assessment diagnose rotator cuff injuries?

No. It measures muscle force only and should always be interpreted alongside symptoms and other assessment findings.

Key Takeaways

• Measures maximal isometric shoulder internal rotation strength.

• Performed with the shoulder adducted and the elbow flexed to 90°.

• Primarily assesses the subscapularis and larger shoulder internal rotators.

• Peak force is the primary routine outcome measure.

• Consistent positioning and forearm contact point improve repeatability.

• Baseline comparison and repeated testing are generally more valuable than broad population norms.

References

Bohannon, R. W. (1997). Reference values for extremity muscle strength obtained by hand-held dynamometry from adults aged 20 to 79 years. Archives of Physical Medicine and Rehabilitation, 78(1), 26–32.

Stark, T., Walker, B., Phillips, J. K., Fejer, R., & Beck, R. (2011). Hand-held dynamometry correlation with the gold standard isokinetic dynamometry: A systematic review. PM&R, 3(5), 472–479.

Mentiplay, B. F., Perraton, L. G., Bower, K. J., Adair, B., Pua, Y. H., Williams, G. P., McGaw, R., & Clark, R. A. (2015). Assessment of lower limb muscle strength and power using hand-held and fixed dynamometry: A reliability and validity study. PLOS ONE, 10(10), e0140822.