Active Knee Extension (AKE) Test: How to Measure Hamstring Flexibility

Tight hamstrings are one of the most common findings in any flexibility assessment, but "can you touch your toes" isn't a very reliable measure: it depends on arm length, lumbar mobility, and a dozen other factors. The Active Knee Extension Test (AKE), also known as the 90/90 test, isolates the hamstring muscles much better and gives a value in degrees that's easy to compare over time.

If you work with injury rehab, runners, or simply want an objective measure of posterior chain flexibility, this test should be part of your protocol.

What does this test measure?

It measures the active knee extension deficit when the hip is fixed at 90° of flexion — that is, how far the leg is from reaching full extension (0°) due to hamstring resistance. The larger this deficit in degrees, the lower the hamstring flexibility.

Unlike a Sit and Reach, the AKE controls hip and pelvis position, so it better isolates the hamstring component and is less sensitive to spinal compensations.

Equipment needed

• A table or flat surface where the person can lie supine
• Goniometer (or a goniometry app on a phone)
• Optional: a square or strap to hold the thigh at 90°

Step-by-step protocol

1. The person lies supine, with both legs extended on the table
2. Flex the hip of the leg being tested to 90°, while also keeping the knee flexed (the "90/90" position)
3. The other leg stays extended and resting on the table
4. Ask the person to actively extend the knee as far as possible, without the hip moving away from 90° and without the pelvis lifting
5. Place the goniometer with the axis at the lateral femoral condyle, one arm toward the greater trochanter and the other toward the lateral malleolus
6. Measure the extension deficit angle relative to 0° (full knee extension)
7. Repeat 2-3 times per leg and record the best value

Common mistakes

• Letting the hip flex past 90° or the pelvis lift to "gain" range
• Not stabilizing the thigh properly during knee extension
• Confusing active with passive extension: here the movement is performed by the person themselves, without external help
• Not comparing both legs

How to interpret the results

Extension deficit	Interpretation
0-20°	Normal hamstring flexibility
20-30°	Reduced flexibility — pay particular attention in runners
> 30°	Significant tightness — flexibility/mobility work should be a priority
> 5-10° asymmetry between legs	Possible injury risk factor, especially in sprint-based sports

These ranges are a general guide: the most useful approach is usually to compare side to side and track each leg's progress separately over time.

How this test relates to others

The AKE pairs well with:

• Active Straight Leg Raise (ASLR) Test — measures something similar but adds a motor control and core stability component, useful for distinguishing a pure flexibility issue from a control issue
• Sit and Reach Test — for an overall measure of posterior chain and lower back flexibility

Track your progress

What makes the AKE great is that it gives you a number in degrees for each leg, ideal for tracking progress with a mobility program or spotting asymmetries that aren't improving. With Movalytics you can record the extension deficit of each leg at every assessment and automatically compare progress over the weeks — much more reliable than relying on memory or scattered notes.

FAQ

Is the AKE the same as the Sit and Reach? No. The Sit and Reach is an overall measure of posterior chain and lower back flexibility, while the AKE specifically isolates the hamstrings by fixing the hip position. What does "active" mean in this test? That the person extends the knee using their own muscles, without help from the evaluator. This gives a more functional measure than a passive stretch. How often should this test be repeated? Every 4-6 weeks is reasonable if you're working on hamstring flexibility — enough to see real changes without measurement noise distorting the result.