LegsPin machineIsolation — knee flexion

Single-Leg Seated Leg Curl

Reviewed by Bryan Cortez, MS

Pin the thigh, curl one side, and let the weaker leg set the dose.

Rep Sweet Spot

8-15

per side

Sets

2-4

sets per side

RIR

1-3

Canonical coaching profile

Complete coaching guidance, with the evidence boundary visible

This profile is served from the canonical Airtable coaching library. Its theory tier and evidence confidence remain separate source-truth fields.

Theory

Theory tier S

Evidence confidence

Mechanics-led evidence confidence (D)

The tier is a reasoned biomechanics judgment. Evidence grade D is mechanics-led and is not direct hypertrophy proof; the full category evidence-control program remains pending.

Why it ranks: Single-Leg Seated Leg Curl is ranked for Hamstrings because its named path directly expresses loaded knee flexion or hip extension with long hamstring excursion; external support reduces balance and bracing demands. The main limitation is individual joint fit and execution consistency.
Primary limiter: Machine axis, thigh-pad pressure, and pelvic position; poor alignment can make the knee or calf the limiting factor instead of the hamstrings.
Safety and fit: Align the machine pivot with the knee, secure the thigh without excessive compression, and use a pain-free curl and return range.
What would change the call: Reverse or lower the placement if a corrected line-of-force model shows that another limiter owns the task, or if the declared range cannot be progressed repeatably.

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Demonstration

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Physique Skool is filming one canonical demonstration per exercise. Until this movement is published, use the setup, execution, common errors, programming, and substitutions below.

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How to do it

Setup

Align the knee joint with the machine pivot
Set the ankle pad above the heel
Secure the thigh pad and keep the pelvis against the seat
Move the nonworking leg clear without twisting

Execution

Curl the working heel down and back
Keep the thigh heavy under the pad
Pause at the shortest controlled position
Return until the hamstrings are lengthened without the stack resting

Common Errors

Turning the pelvis toward the working leg
Lifting the thigh under the restraint
Pointing the toes to manufacture range
Giving the stronger side extra reps

Cues That Work

Thigh stays pinned; heel curls under; match the weaker side

No-Fly Zone

Avoid rotating the pelvis, lifting the working thigh, or forcing the pad beyond the knee's comfortable flexion range.

Programming

Sequence priority

Flexible

Stable unilateral isolation works well after hip hinges or as the primary knee-flexion slot when correcting a meaningful side-to-side dosing difference.

Progression

Model — Double

Fallback model — Double

Begin with the weaker or less coordinated side, cap the stronger side at the same clean reps, and add load only when both reach the top of the range.

Best program fit

Legs

Load increments

Standardthe smallest selector step matched to the weaker side

Smaller incrementadd reps to the weaker side first or use a fractional stack plate

Larger incrementone full selector increment only when both sides keep the same range

If it hurts

Pain is information, not a challenge to push through. Stop the set if pain is sharp, worsening, or changes how you move. These are exercise-selection options, not medical diagnosis or rehabilitation advice.

Work down this list in order. Stop at the first change that removes the pain.

Step 1
Setup tweaks
Recheck seat depth, knee-axis alignment, and ankle-pad position before changing load.
Step 2
ROM / tempo / bias
Add a controlled two-second return or a one-second curl pause to both sides.
Step 3
Implement swap
Bilateral seated leg curl, lying leg curl, or unilateral cable leg curl.

Substitutions

Approved fallback

Bilateral seated leg curl, lying leg curl, or unilateral cable leg curl.

The Evidence

Unilateral loading reveals and manages side differences, but it does not prove an asymmetry needs correction. Machine fit and individual knee tolerance can change the best curl choice.

SFR — 4.5

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