During a Functional Capacity Evaluation (FCE), lumbar range of motion may provide useful information about an evaluee's physical abilities and impairments. But measuring forward flexion is not always as simple as recording how far someone bends.

Forward trunk flexion is a combined movement involving both the lumbar spine and movement of the pelvis over the hips.

Older editions of the AMA Guides to the Evaluation of Permanent Impairment recognized this and incorporated an additional comparison: passive Straight Leg Raise (SLR).

The purpose was not to diagnose lumbar radiculopathy.

Instead, the Straight Leg Raise provided a second biomechanical measurement that could be compared with the pelvic contribution observed during lumbar flexion and extension.

This makes the SLR comparison an interesting example of a much broader principle in Functional Capacity Evaluation:

A measurement becomes more useful when it can be compared with other related findings obtained under different testing conditions.

This Is Not the Diagnostic Straight Leg Raise Test

The first distinction is important.

Physical therapists commonly associate the Straight Leg Raise with the neurological examination of the lumbar spine and assessment of possible nerve-root involvement.

That is not what is being discussed here.

Within the older ROM-based AMA methodology, passive SLR was used as an accessory validity comparison for lumbar range-of-motion measurement.

The examiner is asking a biomechanical question:

Does the amount of pelvic and hip excursion demonstrated during standing lumbar movement make sense when compared with the available excursion demonstrated during passive Straight Leg Raise?

That is a very different purpose from using SLR as a neurological provocative test.

Why Lumbar Flexion Requires More Than One Measurement

When someone bends forward in standing, all of the observed movement does not occur through the lumbar vertebrae.

Forward bending involves a coordinated relationship between:

• lumbar spine flexion
• anterior pelvic rotation
• hip flexion

This is commonly described as lumbo-pelvic rhythm.

Conceptually:

Total forward trunk movement = lumbar movement + pelvic/hip movement

This is one reason inclinometer-based spinal testing commonly uses more than one measurement location. The evaluator is attempting to distinguish movement occurring through the lumbar spine from movement occurring through the pelvis.

You can read more about the measurement tools themselves in Goniometer versus Inclinometer and Range of Motion Testing with an Inclinometer.

How the Straight Leg Raise Cross-Check Works

During inclinometric lumbar range-of-motion testing, the examiner measures the pelvic or sacral contribution to sagittal movement.

Conceptually, lumbar flexion is determined by separating total trunk movement from the movement occurring through the pelvis.

The examiner also measures sacral movement during extension.

The two sacral measurements are then considered together:

Sacral flexion + sacral extension = total sagittal sacral excursion

Passive Straight Leg Raise is then measured on both sides.

The lower, or tighter, of the two valid SLR measurements becomes the comparison value.

The cross-check can therefore be represented simply as:

Tightest SLR ↔ Sacral Flexion + Sacral Extension

The numbers do not have to be identical.

The tests are not measuring exactly the same activity.

However, because both findings provide information about available hip, pelvic, and posterior-chain excursion, the relationship should be biomechanically plausible.

Why Does This Provide an Internal Validity Check?

Consider an evaluee who demonstrates very restricted pelvic movement during active forward bending.

The standing measurement appears to suggest that only a small amount of hip and pelvic excursion is available.

The evaluee is then positioned supine and demonstrates substantially greater excursion during passive Straight Leg Raise.

Now the evaluator has two related findings obtained under different conditions that do not appear to tell the same story.

That does not immediately tell the evaluator why they are different.

It does tell the evaluator that the standing range-of-motion result deserves further consideration.

An Example of the SLR Comparison

Imagine the following measurements:

Standing Lumbar ROM Testing

• Sacral flexion: 40°
• Sacral extension: 10°
• Total sacral excursion: 50°

Passive Straight Leg Raise

• Right SLR: 72°
• Left SLR: 75°
• Tightest SLR: 72°

The difference between the tightest SLR and the measured sacral excursion is therefore:

72° − 50° = 22°

Under the accessory validity criteria used in the older AMA ROM methodologies, a discrepancy of this magnitude would cause the lumbar flexion measurement to fail that particular internal validity check.

That finding should trigger another question:

Why do these two related measurements differ?

Possible explanations need to be investigated rather than assumed.

The AMA Edition Matters

There is not one universal "AMA 10-degree rule."

The criteria changed between editions of the AMA Guides.

In the Third Edition Revised, the comparison between the summed sacral flexion and extension measurements and the tightest Straight Leg Raise used an approximately 10° allowable difference.

In the Fifth Edition, the accessory SLR validity procedure allows a difference of up to approximately 15° when that accessory validity test is indicated.

That distinction matters when teaching or applying the procedure.

Clinicians should identify which edition and jurisdictional methodology they are working under rather than referring generically to an "AMA rule."

It is also important to recognize that this Straight Leg Raise cross-comparison comes from the older ROM-based spinal impairment methodology. It should not be presented as a universal requirement of every contemporary Functional Capacity Evaluation.

Repeatability and Cross-Validation Are Not the Same Thing

This is where the concept becomes particularly useful for FCE clinicians.

Repeatability asks:

Can the evaluee produce reasonably consistent results when the same measurement is repeated?

Cross-validation asks:

Does this result make sense when compared with a different but related measurement?

An evaluee could theoretically demonstrate three highly repeatable lumbar flexion measurements.

If those measurements are all substantially inconsistent with another related biomechanical finding, repeatability alone does not resolve the discrepancy.

That is why repeated measurements and cross-comparisons provide different information.

The same principle appears elsewhere in FCE practice.

An evaluator may compare:

• repeated grip-strength trials
• dynamic and isometric force production
• heart-rate response and perceived exertion
• reported ability and demonstrated ability
• physical examination findings and functional performance
• performance of similar movements during different activities

For more on repeat testing, see Why Do We Measure More Than Once in a Functional Capacity Evaluation?.

A Failed SLR Cross-Check Does Not Mean the Evaluee Is "Invalid"

This may be the most important clinical point.

If the Straight Leg Raise comparison does not satisfy the accessory validity criterion, the conclusion should not automatically be:

The evaluee is malingering.

It should not even automatically be:

The entire FCE is invalid.

The more precise conclusion is that the specific lumbar flexion measurement has demonstrated an inconsistency that requires interpretation.

Possible contributors may include:

• measurement variability
• pain
• fear or guarding
• difficulty understanding the test
• changes associated with warm-up
• differences between active and passive movement
• strength deficits
• technical measurement error
• self-limited active performance

The evaluator then determines what weight should be placed on that measurement when interpreting the complete evaluation.

Active and Passive Motion Consistency in Modern FCE Practice

The same general principle remains relevant even when an evaluator is not performing an AMA impairment rating.

The 2022 Functional Capacity Evaluation and Disability Determination monograph specifically identifies active and passive motion consistency as one of the findings that may contribute to performance-validity interpretation.

It also cautions clinicians against oversimplifying that comparison.

Active and passive movement may differ for legitimate clinical reasons. Pain, fear-avoidance, muscle weakness, pathology, motor control, and other factors can affect active performance.

The existence of a difference is therefore not the conclusion.

The difference is a finding that must be explained.

Performance Validity Requires the Preponderance of Evidence

Current Functional Capacity Evaluation best-practice guidance takes an even broader approach.

The Current Concepts in Functional Capacity Evaluation guideline recommends that conclusions regarding performance or effort be based on the preponderance of data.

The evaluator considers information including:

• physiological endpoints
• biomechanical endpoints
• psychophysical endpoints
• reported symptoms
• clinical examination findings
• movement consistency
• performance consistency
• observed pain behaviours

No single measurement should be asked to answer a question it cannot answer.

This is also why measures such as coefficient of variation, repeated range of motion, grip testing, heart-rate response, and biomechanical observations are most useful when interpreted together rather than independently.

The Bigger FCE Principle: Does Everything Fit Together?

The value of the Straight Leg Raise comparison extends beyond the specific AMA formula.

It demonstrates a fundamental principle of high-quality Functional Capacity Evaluation:

Do not rely on one measurement when another part of the evaluation can help you test whether that measurement makes sense.

The physical examination, functional testing, observed biomechanics, symptoms, physiological responses, and repeated measurements should gradually build a coherent picture of the evaluee's abilities and limitations.

Sometimes the evidence aligns.

Sometimes it does not.

When it does not, the evaluator's responsibility is not to jump immediately to a behavioural conclusion.

The responsibility is to investigate the inconsistency, determine whether there is a reasonable explanation, repeat or modify testing when appropriate, and explain how the finding affects confidence in the final opinion.

That approach is more consistent with contemporary FCE best-practice principles than allowing any single "validity test" to determine the outcome of the evaluation.

Frequently Asked Questions

Why is Straight Leg Raise compared with lumbar flexion?

Older AMA Guides methodologies use passive Straight Leg Raise as an independent comparison of available hip and posterior-chain excursion. The tightest SLR is compared with the sacral excursion measured during lumbar flexion and extension to determine whether the measurements demonstrate a reasonably consistent biomechanical relationship.

Is this the same Straight Leg Raise used to test for radiculopathy?

No. The movement may look similar, but the purpose is different. In this context, Straight Leg Raise is being used as an accessory measurement-validity comparison rather than as a neurological provocative test.

What is compared with the Straight Leg Raise measurement?

The tightest valid passive Straight Leg Raise is compared with the sum of measured sacral flexion and sacral extension.

Does a failed SLR comparison prove poor effort?

No. It demonstrates an inconsistency between related measurements. The evaluator must investigate possible explanations and interpret the finding with the rest of the physical examination and functional testing data.

Does a failed SLR comparison make the entire FCE invalid?

No. The comparison relates to the credibility of a specific lumbar range-of-motion measurement. Overall FCE performance validity should be determined from the preponderance of evidence across the evaluation.

What is the AMA Straight Leg Raise validity threshold?

The criterion depends on the AMA Guides edition. The Third Edition Revised used an approximately 10° relationship, while the Fifth Edition accessory procedure permits approximately 15°. Clinicians should confirm the requirements of the edition and jurisdiction they are applying.

Why compare active and passive range of motion during an FCE?

Comparing active and passive movement can help identify whether findings are internally consistent and whether additional investigation is required. Differences may be caused by pain, weakness, guarding, pathology, fear, measurement variability, or other clinical factors, so the comparison must be interpreted rather than treated as a standalone validity test.

Is repeatable range of motion automatically valid range of motion?

Not necessarily. Repeatability demonstrates consistency across repeated measurements. Cross-validation asks whether those measurements are also consistent with other related clinical findings. Both can contribute useful information.

Related Functional Capacity Evaluation Articles

• Goniometer versus Inclinometer
• Range of Motion Testing with an Inclinometer
• Why Do We Measure More Than Once in a Functional Capacity Evaluation?
• Understanding Coefficient of Variation in Functional Capacity Evaluations
• Intent and Scope of the FCE Best Practice Guidelines
• Occupational Rehabilitation

Learn More About Functional Capacity Evaluation Training

Metriks Functional Capacity Evaluation Certification teaches rehabilitation professionals how to design, perform, interpret, and report Functional Capacity Evaluations using an evidence-informed clinical reasoning process.

The course addresses physical examination, range-of-motion measurement, test selection, biomechanics, performance consistency, progressive functional testing, performance-validity interpretation, and defensible report writing.

Learn more about Metriks Functional Capacity Evaluation Certification.

References

• American Medical Association. Guides to the Evaluation of Permanent Impairment. 3rd ed., revised. Chicago: American Medical Association; 1990.
• American Medical Association. Guides to the Evaluation of Permanent Impairment. 5th ed. Chicago: AMA Press; 2001.
• Allison S, Galper J, Hoyle D, Mecham J. Current Concepts in Functional Capacity Evaluation: A Best Practices Guideline. 2018.
• MacMasters W, Allison S, Wickstrom R, McMenamin P. Functional Capacity Evaluation and Disability Determination. Academy of Orthopaedic Physical Therapy, APTA; 2022.
• Zuberbier OA, Hunt DG, Kozlowski AJ, et al. Commentary on the American Medical Association Guides' lumbar impairment validity checks. Spine. 2001;26(24):2735-2737. doi:10.1097/00007632-200112150-00023. PubMed.