Exercise Overview

The single leg squat (SLS) is one of the most challenging and revealing exercises in ACL rehabilitation. It demands quad strength, hip stability, balance, and neuromuscular control—everything needed for safe return to sport.

                            Why Single Leg Squats Matter
                            Assessment tool: Reveals strength deficits and movement quality
Return-to-sport criteria: Often part of testing batteries
Maximum demand: Full bodyweight on one leg
Knee control: Shows whether you can control knee valgus
Sport transfer: Running and jumping are single-leg activities

                        

Prerequisites

Before attempting single leg squats, you should be able to:

Perform full depth double-leg squats with good form
Do step-ups on a high box (12"+) with control
Complete lunges without knee valgus
Have quad LSI of at least 70%

How To Perform

1

Starting Position

Stand on one leg with arms extended forward for counterbalance. The non-stance leg is held slightly forward.

2

Initiate the Squat

Push your hips back slightly and begin bending your knee. Keep your chest up and core engaged.

3

Lower with Control

Descend slowly, keeping your knee tracking over your toes. Don't let your knee cave inward. Go as deep as you can maintain good form.

4

Watch Your Alignment

Your knee should stay aligned with your second toe. Pelvis stays level (no dropping on the free leg side).

5

Stand Up

Drive through your heel to return to standing. Maintain balance throughout.

Quality Criteria

A good single leg squat demonstrates these qualities:

Knee Alignment

Knee stays over toes throughout—no inward collapse (valgus) or excessive outward drift.

Pelvis Level

Hips stay level—no dropping on the free leg side (Trendelenburg sign).

Trunk Control

Torso stays relatively upright—no excessive forward lean or lateral shift.

Depth

Can achieve at least 60° knee flexion with good form (deeper is better when controlled).

Recording Yourself

Video your single leg squats from the front and side. Compare your surgical and non-surgical legs. Look for asymmetries in depth, knee control, and stability. This is a common return-to-sport assessment.

Common Mistakes

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Knee Valgus

The knee collapses inward—the most concerning compensation. Stop, regress, and work on hip strength.

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Hip Drop

The pelvis drops on the free leg side, indicating weak hip abductors. Do more clamshells and side-lying exercises.

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Trunk Lean

Excessive forward or lateral lean compensates for weakness. Work on core stability.

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Limited Depth

Can't get to 60° without form breakdown. May indicate quad weakness or ankle mobility issues.

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Speed/Bounce

Using momentum instead of strength. Slow, controlled movement reveals true ability.

Progressions

Assisted SLS

Hold a doorframe, TRX, or pole for support. Use as little assistance as possible. Great starting point.

Beginner

Box Single Leg Squat

Squat down to touch a box behind you. Adjust box height to control depth. Progress to lower boxes.

Intermediate

Skater Squat

Rear leg goes behind you (like a curtsy). Less ankle mobility needed than pistol squat.

Intermediate

Full SLS (No Box)

Free-standing single leg squat to at least 60°. The standard for testing.

Advanced

Pistol Squat

Full depth with front leg extended. Requires significant strength, mobility, and balance. Long-term goal.

Expert

Weighted SLS

Add dumbbells or weight vest once bodyweight SLS is solid. Builds serious strength.