Repetition Maximum Testing: Single Leg (SL) Leg Extension

The Single-Leg Leg Extension Repetition Maximum Test assesses machine-based knee-extension strength on one leg at a time. It is useful for tracking quadriceps strength, comparing sides and monitoring progress across lower-limb strength programmes.

Introduction

A client may show visible side-to-side difference during squats, step-downs or sit-to-stand tasks. Another client may be rebuilding knee-extension strength after a period of reduced training. The Single-Leg Leg Extension Repetition Maximum Test gives professionals a controlled way to assess unilateral knee-extension strength.

The result should be interpreted as machine-based knee-extension performance, not as a complete measure of knee function or lower-limb capacity.

Quick Summary

Test name: Single-Leg Leg Extension Repetition Maximum Test
Purpose: Assess single-leg knee-extension strength
What it assesses: Machine-based quadriceps/knee-extension performance
Equipment: Leg extension machine, load stack or plates, Measurz for recording
Key finding: Maximum load completed for the target repetition standard
Best used with: Squat testing, leg press, sit-to-stand, jump testing and knee ROM tests
Key limitation: It does not measure full lower-limb function on its own

What Is the Single-Leg Leg Extension Repetition Maximum Test?

The Single-Leg Leg Extension Repetition Maximum Test measures the maximum load a client can extend through a defined knee-extension range for a target number of repetitions on one leg.

The test may be performed as a 1RM, 3RM, 5RM or another repetition maximum. The chosen repetition target must be recorded.

Why It Is Used

This test is used to assess unilateral knee-extension strength, compare sides, guide training loads and monitor progress.

It may be useful for lower-limb strength testing, knee strength monitoring, gym programming and performance profiling.

What It Measures

The test measures single-leg leg extension performance.

It may reflect:

Quadriceps knee-extension strength
Load tolerance
Side-to-side difference
Strength progress
Pain response
Control through the tested ROM

It does not measure whole-leg strength, squat ability, jump ability, knee health or sport readiness.

Who It Is Useful For

This test may be useful for gym clients, field sport athletes, older adults, lower-limb strength clients and people needing measurable knee-extension strength tracking.

It may not be appropriate when the machine setup causes symptoms, the client cannot control the movement or maximal testing is not suitable.

Equipment Required

Leg extension machine
Load stack or plates
Adjustable seat/backrest
Adjustable shin pad
Measurz for recording
Optional metronome
Optional video

Step-by-Step Protocol

1. Set the machine

Adjust the seat, backrest and shin pad. Align the knee as closely as practical with the machine axis. Record all machine settings.

2. Define ROM

Decide the starting knee angle and finishing range. The same ROM must be used for both sides and retesting.

3. Define the RM target

Choose whether testing is 1RM, 3RM, 5RM or another repetition maximum.

4. Warm up

Use light warm-up sets and gradually increase load. Avoid testing maximal attempts without familiarisation.

5. Test one side

Ask the client to extend the knee through the agreed ROM with control. Avoid swinging, hip lift or shortened range.

6. Rest and progress

Allow adequate rest between attempts. Increase load only when the previous attempt meets the required standard.

7. Record the best successful result

The score is the heaviest load completed for the target repetition range with acceptable technique.

Scoring and Interpretation

Record side, load, reps and target RM. If estimating 1RM from submaximal reps, label the result as estimated.

Interpret using absolute load, side-to-side comparison, bodyweight context, symptoms, ROM and previous baseline.

A lower score may suggest reduced machine-based knee-extension strength under the tested setup, but it does not identify the cause or represent full knee function.

Normative Data, Benchmarks or Reference Values

Machine-based leg extension values vary widely by equipment, lever arm, ROM, age, sex, training history and body size. Avoid universal norms unless they match the machine and population.

Use the client’s baseline, side-to-side comparison and progress across sessions as the primary benchmarks.

Reliability and Validity

Repetition maximum testing can be reliable when procedures are consistent. A 2020 systematic review supports good-to-excellent reliability for 1RM testing across exercises when familiarisation and standardised protocols are used.  

For leg extension testing, setup consistency is especially important because seat position, pad placement and ROM affect the score.

Common Errors and Testing Limitations

Common errors include poor knee-axis alignment, changing pad position, using momentum, lifting the hips, shortening ROM, comparing results across different machines and ignoring pain.

The main limitation is that the test measures open-chain knee-extension performance only.

Practical Applications

Use this test to monitor knee-extension strength, compare sides, guide training loads and support lower-limb strength tracking.

It is most useful when combined with leg press, squat, sit-to-stand, jump, hop and knee ROM tests.

How to Record This in Measurz

Record side, machine type, seat setting, pad setting, knee angle/ROM, load, reps, RM target, RPE, pain score, symptom location, compensation notes, comparison side and retest date.

Useful notes include shortened ROM, hip lift, pain-limited effort, fast eccentric, poor control or side-to-side difference.

Related Tests or Internal Linking Suggestions

Single-Leg Leg Press Test
Back Squat 1RM Test
Single-Leg Sit-to-Stand
5-Time Sit-to-Stand Test
Vertical Jump Test
Knee Extension ROM Test

FAQs

What does the Single-Leg Leg Extension Test measure?

It measures machine-based knee-extension strength on one leg.

Is it a complete quadriceps test?

It provides useful knee-extension strength information, but it does not measure all lower-limb function.

Should the same machine be used for retesting?

Yes. Different machines can produce different results.

How should side differences be interpreted?

Side differences should be interpreted with pain, ROM, strength history and functional tests.

Should pain be recorded?

Yes. Pain score and symptom location are important for interpretation.

Key Takeaways

The test measures single-leg leg extension performance.
Machine setup and ROM must be standardised.
Do not treat the result as full lower-limb function.
Record side, load, reps and symptoms in Measurz.
Use with squat, leg press and functional tests.

References

Grgic, J., Lazinica, B., Schoenfeld, B. J., & Pedisic, Z. (2020). Test-retest reliability of the one-repetition maximum strength assessment: A systematic review. Sports Medicine - Open, 6, 31.

Suchomel, T. J., Nimphius, S., Bellon, C. R., & Stone, M. H. (2018). The importance of muscular strength: Training considerations. Sports Medicine, 48(4), 765–785.

Weakley, J., Mann, B., Banyard, H., McLaren, S., Scott, T., & Garcia-Ramos, A. (2021). Velocity-based training: From theory to application. Strength and Conditioning Journal, 43(2), 31–49.