Home > Knee Injury, Movement Dysfunction > Single Leg Squat Is a Valid and Reliable Assessment of Hip Muscle Function

Single Leg Squat Is a Valid and Reliable Assessment of Hip Muscle Function

Crossley KM, Zhang WJ, Schache AG, Bryant A, Cowan SM.  Performance on the single-leg squat task indicates hip abductor muscle function.  Am J Sports Med. 2011 Apr;39(4):866-73. Epub 2011 Feb 18.

http://www.ncbi.nlm.nih.gov/pubmed/21335344

Purpose and Rationale:  Several recent studies have demonstrated altered hip muscle function in people with anterior knee pain (patello-femoral pain).  Thus, hip muscle function has been identified as an important factor to address during the prevention and rehabilitation of knee injuries (e.g. patello-femoral pain, ACL injury).  However, many other factors have also been shown to be associated with anterior knee pain (e.g. foot structure, ankle dorsiflexion motion, vastus medialis activation, etc…).  Each of these factors associated with anterior knee pain will likely require a different intervention strategy for successful prevention / rehabilitation of knee injury.  To more efficiently implement knee injury prevention / rehabilitation programs there is a need for a valid and reliable clinical assessment of hip muscle function so that they may receive the most appropriate prevention / rehabilitation strategy.  The purpose of this study was to evaluate reliability of the single leg squat test as a measure of hip muscle dysfunction.  This study also compared hip muscle strength and activation between those with “poor” and “good” hip muscle function during the single leg squat test.

Overview of Research Methods:  The single leg squat test was performed by having subjects stand on top of a 20-cm high box.  The subject’s crossed their arms across their chest and used their dominant leg (kicking leg) was used to lower the opposite foot toward the ground.  This was repeated 5 times in consecutive manner at a rate of approximately 1 squat every 2 seconds.

The following criteria (5) were used to evaluate the subject’s performance on the single leg squat test:

1) Overall Impression Across 5 Trials: 1) Ability to maintain balance; 2) Perturbation of the person (smooth movement); 3) Depth of the squat (at least 60 deg); 4) Speed of the squat (performed at appropriate speed)

2) Trunk Posture (does not commit the following errors): 1) Trunk/thoracic lateral deviation or shift; 2) Trunk/thoracic rotation; 3) Trunk/thoracic lateral flexion; 4) Trunk thoracic forward flexion

3) Pelvis “in space” (does not commit the following errors): 1) Pelvic shunt or lateral deviation; 2) Pelvic rotation; 3) Pelvic tilt

4) Hip Joint (does not commit the following errors): 1) Hip adduction; 2) Hip internal rotation

5) Knee Joint (does not commit the following errors): 1) Apparent knee valgus; 2) Knee position relative to foot position (knee center does not remain over foot center)

Subjects were categorized into 1 of 3 categories based on their single leg squat performance:

Good: Must achieve all of the requirements for 4 of 5 criteria on all 5 trials

Poor: Did not meet all requirements for at least 1 criterion for all of the trials

Fair: Those who were not good or poor were classified as Fair

Reliability of the single leg squat test was performed by comparing the ratings of 5 separate physical therapists after watching a video that demonstrated how to properly score the single leg squat test.  Validity of the single leg squat test was performed by comparing the strength of the hip abductors, hip external rotators, and lateral trunk musculature between the Good and Poor groups.  Validity was also assessed by comparing the muscle activation patterns of the anterior and posterior gluteus medius muscles between the Good and Poor groups.

Key Findings:

  • Overall, there was excellent to substantial agreement across the raters using the scoring criteria outlined above
  • Hip abduction strength and lateral trunk strength (assessed with the side bridge test) were 29% and 23%  lower in the Poor group compared to the Good group.  There was no difference in hip external rotation strength between groups.
  • Onset of anterior and posterior gluteus medius activation was slower in the Poor group compared to the Good group

Clinical Implications:  These findings indicate that after viewing a training video raters are able to reliably score the single leg squat test using the criteria outlined above.  Thus, the single  leg squat test as described by Crossley et al appears to be a reliable clinical assessment tool.

Individuals who performed “Poor” on the single leg squat test had significantly weaker hip abductor and lateral trunk musculature combined with slower onset of the gluteus medius muscle during a step up task.  These findings indicate that the single leg squat test is a valid indicator of hip muscle function as those who score “poor” do appear to have hip muscle dysfunction (weaker and slower muscle activation onset).

Based on this study the single leg squat test appears to be a reliable and valid clinical assessment of hip muscle function.  Individuals who demonstrate “Poor” hip muscle function may benefit from exercises to improve hip neuromuscular control and strength.  Future research is needed to determine if such an exercise program in those with “poor” hip muscle function can improve knee injury prevention / rehabilitation efforts.

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