Anker: Shoulder Abduction Strength Test

The Shoulder Abduction Strength Test measures the maximum isometric force produced as the arm moves away from the side of the body in the frontal plane. Using the Anker, the assessment provides an objective and repeatable measure of shoulder abductor strength in a standardised position.

Shoulder abduction strength is essential for overhead reaching, lifting, carrying, throwing, racquet sports and many occupational tasks. It also contributes to glenohumeral stability by maintaining appropriate humeral head positioning during arm elevation.

The primary muscles assessed include the middle deltoid and supraspinatus, with assistance from the upper trapezius and serratus anterior to stabilise the scapula.

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 Abduction Strength Test?

The Shoulder Abduction Strength Test is an isometric assessment where the client attempts to lift the arm away from the body while maintaining a stable shoulder girdle and trunk.

The assessment is commonly performed with the shoulder abducted to approximately 90° in the scapular plane, where the glenohumeral joint is positioned comfortably while allowing consistent force production.

The fixed resistance provided by the Anker enables repeatable testing when the same client position, anatomical landmarks and verbal instructions are maintained.

Step-by-Step Protocol

1. Prepare the client

Explain that the assessment measures how strongly they can lift their arm out to the side.

Record any:

• shoulder pain

• upper arm pain

• neck pain

• previous shoulder injury

• previous surgery

• neurological symptoms

• fatigue

Perform 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 abducted to approximately 90° in the scapular plane

• elbow extended or comfortably flexed according to the Anker setup

• thumb pointing upwards if using the scapular plane

Maintain identical positioning during every reassessment.

3. Position the testing limb

Ensure:

• the scapula remains neutral

• the humerus remains aligned in the scapular plane

• the elbow remains stable

• the wrist remains relaxed

Position the Anker load cell against the lateral aspect of the distal humerus, approximately 5 cm proximal to the lateral epicondyle.

Avoid direct contact over the elbow joint.

Record the contact point for consistent retesting.

4. Stabilise the client

Prevent movement of:

• trunk

• pelvis

• opposite shoulder

• excessive scapular elevation

The effort should occur through shoulder abduction rather than trunk side flexion.

5. Testing instructions

Use consistent verbal instructions.

"Lift your arm out to the side."

"Increase the pressure smoothly."

"Push as hard as you can."

"Hold."

"Keep breathing."

Repeat the same wording 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:

• the highest force value, or

• the average of the recorded trials

Maintain the same scoring method for future assessments.

7. Repeat the trial if

• the trunk leans

• the shoulder elevates

• the elbow changes position

• the scapula excessively elevates

• the load cell slips

• pain limits maximal effort

• the client starts before instructed

Why It Is Used

The assessment may be useful for:

• establishing baseline shoulder strength

• comparing left and right limbs

• monitoring strength over time

• athlete performance profiling

• objective reporting using Measurz

• monitoring response to exercise

• client education

The assessment should support broader assessment reasoning and should not be used as a stand-alone diagnostic or clearance assessment.

What It Measures

The primary outcome is peak isometric shoulder abduction 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 stability

• shoulder mobility

• movement quality

• overhead performance

• readiness for work or sport

Understanding the Result, Reference Values and What to Look For

Higher force values generally indicate greater shoulder abduction strength.

Lower force values may reflect:

• pain

• fatigue

• previous injury

• reduced effort

• inconsistent positioning

• movement compensation

Interpret results by considering:

• previous assessment results

• left versus right differences

• symptoms during testing

• movement compensations

• occupational, sporting and daily-life demands

Published Anker-specific normative values are currently unavailable.

Shoulder abduction dynamometry has demonstrated excellent repeatability when testing position, lever arm and stabilisation are standardised. Repeated testing using the same protocol provides more meaningful information than comparison with external reference values.

A side-to-side difference of approximately 10% or greater may warrant further assessment when consistent with symptoms or reduced function.

Assessing Different Client Populations

Youth

Interpret relative to growth, coordination and sporting participation.

Adults

Useful for baseline assessment and monitoring progress.

Older adults

Interpret alongside reaching ability, lifting tasks and daily activities.

Athletes

Particularly useful for overhead athletes, swimmers, climbers, volleyball players, tennis players and strength athletes.

Clients with persistent symptoms

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

Common Errors and Limitations

Common errors include:

• trunk leaning

• shoulder elevation

• scapular shrugging

• elbow movement

• 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

• side-to-side comparison

• athlete profiling

• objective reporting within Measurz

• educating clients using measurable outcomes

FAQs

What does the Shoulder Abduction Strength Test measure?

It measures maximal isometric shoulder abduction strength.

Why is the scapular plane commonly used?

Testing in the scapular plane places the shoulder in a comfortable position that is often better tolerated while maintaining good repeatability.

Which metric should be used routinely?

Peak force is the primary outcome measure.

Should both shoulders be tested?

Yes. Bilateral testing allows meaningful comparison.

Can this assessment diagnose rotator cuff pathology?

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

Key Takeaways

• Measures maximal isometric shoulder abduction strength.

• Primarily assesses the middle deltoid and supraspinatus.

• Peak force is the primary routine outcome measure.

• Consistent positioning and load cell placement improve repeatability.

• Measurz provides additional force-time metrics.

• Compare results with previous assessments and the opposite shoulder.

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.