The single leg squat test is one of the most informative and most widely used movement screening assessments in sports medicine and physiotherapy. In approximately 30 seconds per leg, a trained observer can identify hip abductor weakness, hip external rotator insufficiency, quadriceps control deficits, and the dynamic knee valgus pattern that is the primary biomechanical risk factor for ACL injury, patellofemoral pain, and IT band syndrome.
It is the same movement as the single leg squat exercise covered in the single leg squats article on this site, but the purpose is fundamentally different: the exercise is a training stimulus, the test is an assessment tool. The training context allows modification and progression based on ability. The testing context requires a standardised protocol that produces comparable results over time and between individuals.
What the Single Leg Squat Test Assesses
The single leg squat test places the lower extremity under a controlled, standardised load (body weight on one leg through a squat movement) and reveals how well the neuromuscular system controls the position of the knee, hip, and pelvis under that load.
What the test specifically reveals:
Knee valgus control: The most important finding. The degree to which the knee drifts inward during the single leg squat reflects the combined sufficiency of the gluteus medius, hip external rotators, and quadriceps in controlling femoral and tibial position. As covered in the what is knee valgus article on this site, dynamic knee valgus during the single leg squat is associated with ACL injury risk, patellofemoral pain, and IT band syndrome.
Gluteus medius function: Pelvic drop on the non-standing side during the test (Trendelenburg sign) specifically indicates insufficient gluteus medius function on the standing side.
Overall lower extremity movement quality: The test provides a global view of how the entire lower extremity kinetic chain (hip, knee, ankle, foot) works together under single-leg loading.
Side-to-side asymmetry: Comparing test findings between sides identifies asymmetries that bilateral assessments miss and that may indicate elevated injury risk on the worse-performing side.
How the Single Leg Squat Test Differs From the Exercise
As an exercise: The single leg squat is modified to match the person’s current ability. Assistance is provided (box, TRX), depth is adjusted, and progressions are used based on the training goal. Form issues are corrected through cueing and the exercise is adapted.
As a test: The single leg squat test uses a standardised protocol so that findings can be compared across sessions and individuals. No coaching or cueing is provided during the test movement itself (cueing changes the movement and invalidates the natural assessment). The test reveals what the movement looks like without instruction.
Why this distinction matters: If you coach a person through their natural single leg squat before testing it, you will see their coached movement rather than their natural movement pattern. The test must be performed without correction to be a valid assessment.
How to Perform the Single Leg Squat Test
Standardised Protocol
The standard single leg squat test protocol used across most research and clinical settings:
Equipment needed:
- A firm, flat surface
- A camera or observer positioned directly in front of the athlete (frontal plane view)
- Optionally, a side view camera for sagittal plane assessment
Instructions to the athlete:
- Stand on one leg with the foot pointing straight ahead
- Place the hands on the hips
- The non-standing leg should be held with the knee bent at approximately 90 degrees and the foot behind the body, or extended to the front (protocol varies slightly between sources; the key is consistency within a testing session)
- Squat to approximately 60 degrees of knee flexion (a single-leg quarter to half squat)
- Return to standing
- Perform 5 repetitions per leg
- Rest 2 minutes between sides
What is observed:
The observer (or camera) watches from directly in front during all 5 repetitions on each side, specifically noting:
- Knee position relative to the second and third toe
- Pelvic level (does either hip drop?)
- Trunk position (does the trunk lean to one side?)
- Foot and ankle behaviour (heel rise, foot pronation)
Depth Standardisation
The standard depth for the single leg squat test is approximately 60 degrees of knee flexion. This corresponds to approximately a quarter to half squat position. The rationale for 60 degrees rather than full depth is that:
- It is a depth that most people can achieve, making it useful across populations
- The 60-degree range is the depth at which knee valgus typically becomes most apparent in people with control deficits
- It corresponds to the knee flexion angle that occurs during the stance phase of running and during landing tasks
Scoring the Test
Two primary scoring approaches are used in research and clinical practice:
Binary pass/fail: The most common clinical approach. The test is passed if the knee remains aligned over the second and third toe throughout all 5 reps, the pelvis remains relatively level, and the trunk remains upright. The test is failed if significant knee valgus, hip drop, or trunk lean is observed.
Ordinal scale (1 to 3):
- Score 1 (Good): Pelvis level, knee aligned, trunk upright. Minimal to no compensatory movements.
- Score 2 (Fair): Mild knee valgus, mild pelvic drop, or mild trunk lean that does not significantly affect the overall pattern.
- Score 3 (Poor): Significant knee valgus with the knee crossing the midline, significant pelvic drop (Trendelenburg sign), or significant trunk lateral lean.
Research has found that the single leg squat test has moderate to good reliability when performed by trained observers using a standardised protocol. Non-trained observers show significantly less reliability, which is why the test is most accurate when performed by physiotherapists, sports scientists, or coaches familiar with the movement patterns being assessed.
Interpreting Results: What Each Finding Means
Finding 1: Knee Valgus (Knee Crossing Medially)
What it looks like: The standing knee drifts inward during the descent or return, medial to the line of the second and third toes.
What it indicates:
- Insufficient gluteus medius and hip external rotator strength to control femoral adduction and internal rotation under single-leg loading
- Potentially insufficient ankle dorsiflexion (which can drive a compensatory valgus)
- Potentially insufficient VMO function relative to the lateral quad and IT band tension
Clinical significance:
Research by Meeuwisse, Powers, and others has established dynamic knee valgus during the single leg squat as a significant predictor of patellofemoral pain, IT band syndrome, and ACL injury in prospective studies. Female athletes showing significant knee valgus during the single leg squat have been found to have substantially elevated ACL injury risk compared to those with normal alignment.
Severity grading:
- Mild: Knee drifts slightly medially but does not cross the midline of the foot
- Moderate: Knee crosses the midline of the foot but not the great toe
- Severe: Knee crosses the line of the great toe or collapses significantly inward
Finding 2: Pelvic Drop (Trendelenburg Sign)
What it looks like: The non-standing hip drops below the level of the standing hip during the squat.
What it indicates:
- Insufficient gluteus medius strength on the standing side
- The gluteus medius is not producing adequate abduction force to maintain pelvic level against the adduction moment created by body weight over a single leg
Clinical significance:
Pelvic drop during the single leg squat is strongly associated with running-related injuries including IT band syndrome, patellofemoral pain, and hip pain. Research on runners consistently finds greater Trendelenburg angles during running gait in those with IT band syndrome and patellofemoral pain compared to pain-free runners.
Distinguishing pelvic drop from trunk lean:
Pelvic drop involves the non-standing hip dropping below the standing hip. Trunk lean involves the trunk tilting toward the standing side without pelvic drop. Both indicate gluteus medius insufficiency but through slightly different mechanisms:
- Pelvic drop: the gluteus medius cannot maintain pelvic level (classic Trendelenburg)
- Trunk lean: the body compensates for gluteus medius weakness by shifting the centre of mass toward the standing leg to reduce the abductor demand (compensated Trendelenburg)
Finding 3: Trunk Lateral Lean
What it looks like: The trunk tilts toward the standing leg side during the squat.
What it indicates:
- Compensatory Trendelenburg: the body is reducing the abductor demand by shifting the centre of mass, as a compensation for insufficient gluteus medius force production
Clinical significance:
Same as pelvic drop: indicates gluteus medius insufficiency and is associated with the same injury patterns.
Finding 4: Heel Rise
What it looks like: The standing heel lifts off the floor during the descent.
What it indicates:
- Insufficient ankle dorsiflexion range to allow the knee to travel over the toes at the squat depth attempted
Clinical significance:
Heel rise itself is not directly injury-causing but it forces compensatory patterns (excessive trunk lean, toe-dominant foot strike) that transfer abnormal forces to the knee and hip. As covered in the ankle mobility exercises for squats article (from earlier batches on this site), ankle dorsiflexion restriction is a common and addressable contributor to poor single leg squat mechanics.
Finding 5: Normal Single Leg Squat (Pass)
What it looks like: Knee tracks over the second and third toe, pelvis remains level, trunk remains relatively upright, heel flat throughout.
What it indicates:
- Adequate neuromuscular control of the lower extremity for single-leg loading at the tested depth
- Does not guarantee adequate control at greater depths, higher speeds, or under fatigue
Clinical Applications
Pre-Season Athletic Screening
The single leg squat test is used in pre-season athletic screening to identify athletes with movement control deficits before the competitive season. Athletes with significant valgus or pelvic drop are flagged for targeted hip strengthening and movement retraining before their injury risk is elevated by training and competition load.
Research basis: Several prospective studies have found that athletes with greater knee valgus during the single leg squat test at pre-season screening have significantly higher rates of knee injury during the subsequent season compared to those with normal alignment.
ACL Injury Prevention Programmes
As covered in the what is knee valgus article on this site, dynamic knee valgus is the primary ACL injury risk factor. The single leg squat test provides a practical, equipment-free assessment of knee valgus control that can be used to:
- Identify high-risk athletes before injury
- Monitor the response to targeted intervention programmes
- Assess readiness for return to sport following ACL reconstruction
Return-to-Sport Criteria Following Knee Injury
The ability to perform the single leg squat test without significant valgus or pelvic drop is included as a criterion for return to sport in many clinical protocols following ACL reconstruction, patellofemoral pain management, and knee replacement surgery.
The specific criterion varies between protocols but a common benchmark is: single leg squat to 60 degrees with no knee valgus and no pelvic drop for 5 consecutive reps, symmetrical between sides, before returning to full contact sport.
Patellofemoral Pain Assessment
As covered in the patellofemoral pain syndrome physical exercise article on this site, PFPS is associated with the same hip abductor and external rotator deficits that produce valgus during the single leg squat test. The test is used to:
- Confirm the presence of biomechanical contributors to PFPS
- Monitor improvement during the rehabilitation programme
- Guide exercise selection (focus on the specific deficit revealed by the test)
Running Gait Screening
For recreational and competitive runners, the single leg squat test provides a quick assessment of the hip control quality that determines running mechanics. Runners who fail the test (valgus or pelvic drop) are likely displaying similar patterns during every running stride and are at elevated risk for IT band syndrome, patellofemoral pain, and stress fractures.
Limitations of the Single Leg Squat Test
Observer reliability: The test requires a trained observer to produce reliable results. Self-assessment without video is unreliable. Video from a fixed camera position is the minimum required for accurate self-assessment.
Speed dependency: The test is performed slowly and voluntarily. Sports injuries typically occur at much higher speeds and under reactive conditions. A person who passes the slow, controlled single leg squat test may still demonstrate poor mechanics during high-speed athletic movement.
Depth standardisation: Achieving consistent 60-degree depth across testers is difficult without goniometric measurement. Different depths produce different findings.
Not a diagnostic tool: The single leg squat test identifies movement control deficits but does not diagnose the specific structural cause of those deficits. A positive test (significant valgus, pelvic drop) indicates a need for further assessment rather than a specific structural diagnosis.
Does not account for fatigue: The test is performed fresh. In sport, the most injury-critical moments often occur under fatigue when movement control degrades. A sport-specific fatigue-state assessment (repeated single leg squats or the test performed after a fatigue protocol) may be more relevant for athletic injury risk assessment.
Acting on Test Findings
For Knee Valgus
Priority exercises:
- Clamshell with band: 3 x 15 per side
- Lateral band walk: 3 x 15 steps per direction
- Single-leg glute bridge: 3 x 10 per side
- Fire hydrant: 3 x 12 per side
- Lateral step down: 3 x 10 per side (as covered in the lateral step down exercise article on this site)
Re-test: After 6 to 8 weeks of consistent targeted hip strengthening, re-test using the same protocol to assess improvement.
For Pelvic Drop
Priority exercises:
Same as for knee valgus, as the underlying cause (gluteus medius insufficiency) is the same. Add:
- Monster walk: 3 x 12 steps per direction (as covered in the monster walk resistance bands article on this site)
- Single-leg RDL: 3 x 8 per leg (as covered in the single-leg romanian deadlift article on this site)
For Heel Rise
Priority: Ankle dorsiflexion mobility work. As covered in the ankle mobility exercises for squats article (from earlier batches on this site), consistent ankle dorsiflexion stretching and joint mobilisation typically produces meaningful improvement within 4 to 6 weeks.
Immediate accommodation: A heel elevation of 1 to 2 centimetres allows single leg squat training to continue while ankle mobility is developed.
Frequently Asked Questions
Is the single leg squat test the same as the single leg squat exercise?
They use the same movement but for different purposes. The exercise is used to develop strength and control, with modification, coaching, and progression. The test is used to assess natural movement quality without coaching or modification. The test should always be performed before coaching to capture the athlete’s natural pattern.
How many reps should the single leg squat test include?
Five repetitions per side is the standard used in most research protocols. The first rep or two may show better mechanics as the athlete is fresh and concentrating; later reps under mild fatigue may reveal deficits that do not appear on the first rep. Assessing across all five reps and noting any degradation in quality provides more complete information than a single-rep assessment.
Can I self-test the single leg squat?
You can get useful information from self-testing but with significant limitations. Video from a fixed camera positioned directly in front (frontal plane) and from the side (sagittal plane) provides much better assessment than a mirror, which requires head turning that alters the movement. Slow-motion playback is the most useful self-assessment tool. For accurate clinical assessment, a trained physiotherapist or sports scientist is required.
Does passing the single leg squat test mean I am injury-free?
No. The test assesses a specific movement quality under controlled, slow, low-load conditions. It does not predict injury with certainty in either direction. Athletes who pass the test can still be injured and athletes who fail the test may not be injured. The test provides useful information about one aspect of movement quality that is associated with injury risk, not a definitive prediction.
How often should I re-test?
For athletes in targeted rehabilitation or injury prevention programmes, re-testing every 4 to 6 weeks tracks the response to the programme and guides progression. For healthy athletes not in a specific programme, annual pre-season testing provides a baseline and identifies any changes in movement quality over time.