Repetition Maximum Testing: Leg Curl Test

The Leg Curl Repetition Maximum Test assesses machine-based knee-flexion strength using a standardised leg curl setup. The client completes a maximum-repetition effort with a selected load, then the completed load and repetitions are entered into Measurz so the app can calculate an estimated 1RM.

Introduction

A field sport athlete may need to monitor hamstring strength across a training block. A gym client may want a clear way to track knee-flexion strength. A lower-limb strengthening programme may use the leg curl machine to assess hamstring-focused strength without requiring a hip-hinge pattern.

The Leg Curl Repetition Maximum Test provides a controlled way to assess loaded knee-flexion strength using a standardised machine setup. Rather than requiring a true 1RM attempt, the test can be performed using a submaximal repetition maximum, such as a 3RM, 5RM, 8RM or 10RM. The load and reps are then entered into Measurz to calculate the estimated 1RM.

The result is useful for strength tracking, but it should not be interpreted as a complete measure of hamstring function, sprint performance, running performance, injury risk or return-to-sport readiness.

What Is the Leg Curl Repetition Maximum Test?

The Leg Curl Repetition Maximum Test measures the heaviest load a client can complete for a defined number of repetitions using a leg curl machine.

Depending on the protocol, this may be a 3RM, 5RM, 8RM, 10RM or another repetition maximum. The repetition target should be clearly recorded.

The test may be performed using:

Seated leg curl machine
Prone leg curl machine
Standing leg curl machine
Selectorised leg curl machine
Plate-loaded leg curl machine
Single-leg or double-leg leg curl setup
Other standardised knee-flexion machine setup

In Measurz, the professional records the load and completed repetitions. Measurz then calculates the estimated 1RM from that result. This estimated 1RM can be used to monitor progress over time and guide loading decisions.

If the client performs a true single-repetition maximum, the result should be labelled as a directly measured 1RM. If the result is calculated from a submaximal load and repetitions, it should be labelled as an estimated 1RM.

Why It Is Used

This test is used to assess machine-based knee-flexion strength and track strength changes over time.

It may be useful for athletes, gym clients, lower-limb strength clients and programmes where hamstring-focused strength is a meaningful monitoring variable.

It is especially useful when the professional wants a strength estimate without requiring a true maximal 1RM attempt. A submaximal RM test can be more practical for many clients while still giving a useful estimated 1RM through Measurz.

What It Measures

The test measures leg curl performance under the selected machine setup.

It may reflect:

Machine-based knee-flexion strength
Hamstring-focused loading capacity
Load tolerance
Control through the selected ROM
Pain or symptom response
Estimated 1RM progress across training blocks
Training load progression

It does not measure complete hamstring function, hip-extension strength, sprint performance, running performance, eccentric hamstring capacity, lower-limb injury risk or sport readiness on its own.

Who It Is Useful For

This test may be useful for field sport athletes, gym clients, jumping athletes, runners, lower-limb strength clients and people completing hamstring-focused strengthening programmes.

It may not be appropriate when loaded knee flexion causes unacceptable pain, the client cannot maintain a repeatable machine setup, the test cannot be performed through a consistent ROM, symptoms increase during loaded knee flexion, or the client is not ready for maximal or near-maximal repetition testing.

Equipment Required

Leg curl machine
Load stack or plates
Adjustable seat, bench, pad or lever settings depending on machine type
Measurz for recording load, reps and estimated 1RM
Optional metronome
Optional video
Optional ROM marker or machine-setting note

Step-by-Step Protocol

1. Choose the leg curl setup

Decide whether the test will use a seated, prone, standing, selectorised, plate-loaded, single-leg or double-leg leg curl setup.

2. Record the machine setup

Record machine type, seat or bench position, hip position, knee axis alignment, pad position, ROM, tempo and load method.

3. Choose the repetition target

Select the repetition maximum target, such as 3RM, 5RM, 8RM or 10RM. Use the same target for retesting where possible.

4. Define valid ROM

Set a clear start and finish range. A valid repetition should use the same knee-flexion range each time without hip lift, pelvic rotation, trunk movement, momentum or shortened ROM.

5. Warm up

Complete light warm-up sets. Increase load gradually before testing.

6. Perform the test

Ask the client to complete the selected repetition maximum with controlled movement and the defined ROM.

7. Stop the attempt

Stop when the client reaches the target reps, cannot complete another valid rep, loses ROM, uses unacceptable compensation, reports limiting symptoms or cannot maintain control.

8. Record the maximum successful set

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

9. Enter load and reps into Measurz

Record the completed load and repetitions in Measurz. Measurz calculates the estimated 1RM from the entered result.

Scoring and Interpretation

Record the load, reps and exact leg curl setup. Measurz uses the completed load and reps to calculate the estimated 1RM.

The estimated 1RM should be interpreted as an estimate, not the same as a directly tested 1RM. If a true 1RM was performed, label it as directly measured. If the result comes from a submaximal load and repetitions, label it as estimated.

Interpretation should include:

Absolute load
Completed repetitions
Estimated 1RM
ROM
Machine setup
Tempo
RPE
Pain or symptoms
Compensations
Previous baseline

A lower estimated 1RM may suggest reduced leg curl strength under the tested setup, but it does not identify the cause. Pain, fatigue, machine fit, hip position, knee angle, ROM, confidence, recent training and technique may all influence the result.

Normative Data, Benchmarks or Reference Values

No universal normative value should be applied across leg curl machines and populations. Leg curl results vary by machine design, seated versus prone position, pad position, lever arm, ROM, tempo, training history and whether the 1RM is directly measured or estimated.

Use baseline comparison and progress across sessions as the primary benchmarks.

If a single-leg version is tested, side-to-side comparison can be useful, but it should not be treated as a strict pass/fail rule. A noticeable difference between sides should be interpreted alongside symptoms, training history, sprinting or running demands, lower-limb function and related strength findings.

Machine-based leg curl scores should not be compared across different machines unless the setup is carefully matched.

Common Errors and Testing Limitations

Common errors include changing seat or bench settings, changing pad position, using inconsistent ROM, lifting the hips, rotating the pelvis, using momentum, changing tempo, testing while fatigued, not recording symptoms and comparing results across different machines.

A common recording error is failing to distinguish between a directly measured 1RM and an estimated 1RM. When load and reps are entered into Measurz, the result should be described as an estimated 1RM unless a true 1RM was directly tested.

The main limitation is that the test measures machine-based knee-flexion strength only. It does not fully assess complete hamstring function, hip-extension strength, sprinting, running, jumping, eccentric hamstring capacity, injury risk or sport readiness.

Practical Applications

Use this test to monitor hamstring-focused knee-flexion strength, guide training loads and track response to lower-limb strengthening programmes.

The estimated 1RM can help track progress across training blocks, adjust loading and compare results across retests when the same setup is repeated.

It is most useful when interpreted alongside deadlift, hip thrust, sprint exposure, calf strength, hop testing, lower-limb symptoms and movement quality.

How to Record This in Measurz

Record protocol type, machine type, seated/prone/standing setup, seat or bench position, pad position, ROM, tempo, load, reps, RM target, estimated 1RM, RPE, pain score, symptom location, compensation notes, reason for stopping and retest date.

Useful notes include shortened ROM, hip lift, pelvic rotation, cramping, hamstring discomfort, momentum, pain-limited stop, tempo failure, fatigue-limited attempt, side-to-side difference or machine setup change.

The key Measurz workflow is:

Enter the completed load
Enter the completed reps
Review the estimated 1RM calculated by Measurz
Record machine setup, ROM, symptoms, RPE and compensations
Use the same protocol for retesting

FAQs

What does the Leg Curl Repetition Maximum Test measure?

It measures machine-based knee-flexion strength under the selected leg curl setup.

How does Measurz calculate the result?

The professional enters the completed load and reps into Measurz. Measurz uses this information to calculate the estimated 1RM.

Is the Measurz result a true 1RM?

Not unless the client completed a true 1RM. If the result is based on load and multiple repetitions, it should be labelled as an estimated 1RM.

Is this a hamstring strength test?

It provides useful hamstring-focused knee-flexion strength information, but it does not measure all hamstring functions.

Can results be compared across seated and prone leg curl machines?

Only cautiously. Seated, prone and standing leg curl setups can produce different scores and should not be treated as interchangeable.

Should pain or cramping be recorded?

Yes. Pain score, symptom location, cramping, ROM and whether symptoms limited the result should be recorded.

Is a true 1RM always required?

No. A 3RM, 5RM, 8RM or 10RM may be more appropriate for many clients. Measurz can use load and reps to estimate 1RM.

Key Takeaways

The Leg Curl Repetition Maximum Test measures machine-based knee-flexion strength.
Measurz calculates the estimated 1RM from the recorded load and reps.
Machine setup, pad position and ROM must be repeated for meaningful retesting.
Do not treat an estimated 1RM as the same as a directly measured 1RM.
Do not treat the result as a complete hamstring or lower-limb function profile.
Record load, reps, setup, ROM, symptoms and RPE in Measurz.

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. https://doi.org/10.1186/s40798-020-00260-z

Hoeger, W. W. K., Hopkins, D. R., Barette, S. L., & Hale, D. F. (1990). Relationship between repetitions and selected percentages of one repetition maximum. Journal of Strength and Conditioning Research, 4(2), 47–54.

Kellis, E., Galanis, N., & Natsis, K. (2021). Hamstring muscle activation during strength exercises: Implications for exercise selection. Journal of Functional Morphology and Kinesiology, 6(4), 83.

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.