Background

One of the most common functional movement screens used by clinicians is the single leg squat. A single leg squat requires balance, strength, coordination, and dynamic control of many parts of the body. Due to the high demands of the SLS it can be beneficial in identifying poor movement patterns and compensations in those currently injured or potentially at risk for an injury.

Nakagawa et al 1 found that individuals with Patellofemoral pain performed the SLS with greater ipsilateral trunk lean, contralateral pelvic drop, hip adduction, and knee abduction than those without PFP

Up until this study the position of the non-stance limb had not been assessed on the influence in has on the movement. The purpose of this current study was to compare trunk, pelvis, hip, knee, and ankle kinematics and hip, knee, and ankle kinetics of three variations of the SLS using different non-stance leg positions. This can be beneficial in clinicians during both the assessment and as exercise prescription to target specific muscles  

Methods

16 healthy young women average age of 23 years. No current or recent hx of low back or lower extremity injury in the past 2 weeks. 3d movement was captured using 10 camera motion capture system. 42 retroreflective markers were placed on the trunk, pelvis, and lower extremities.  Participate stood on a force plate and perform a single leg squat with the non-stance leg held in front of the body (SLS front), held in line with the body (SLS middle), or held behind the body line (SLS back). 5 trials of each were collected, and a trial was recollected if the participant lost their balance, did not perform in a fluid motion, or did not hold the stance leg in the proper location for that trial.

Results

 

SLS front

SLS middle

SLS back

Least amount of trunk flexion

Less ankle DF

Greater contralateral pelvic drop

Least ant pelvic tilts

No differences in eversion/inversion

Most increase in hip flexion

Greater plantar flexion moment

 

Most Hip adduction moment

Hip extensor moment

 

Greater hip ER moment

Least appropriate for ACL*

 

Less knee flexion

  

Greater Knee extensor moment

  

Least appropriate for FAI*

*  There was no difference in the hip abductor moment for the three SLS tasks  

Discussion

When comparing the three different contralateral foot positions, the SLS back has the most distinct differences. The SLS back has smaller hip extensor moment, greater knee extensor moment, and greater hip ER moment as compared to the front and middle.

Clinical Relevance

How does this relate to the clinic? Well it might not at all because all the participants were healthy, only female, and no injuries in the trunk or lower extremity. How many of those types of patients have you seen this week? In any case, the SLS back had a higher knee moment so it may be better for assessing quad strength. On the contrary the glute max (hip extensors) and Hamstrings may be better assessed with the SLS front or middle due to the greater moments and potential to detect smaller deficits.

Finally, the SLS back may be less appropriate for patients with suspected FAI (ON THE STANCE LIMB) due to higher degrees of hip flexion and hip adduction. The SLS front may be the least appropriate choice for those with ACL pathology as forces are higher when squatting with minimal forward trunk lean than with moderate forward trunk lean 2.

The largest effects were found at the hip and pelvis between all three variations

Limitations:

All were healthy, no PFP or other injuries which may cause different mechanics. Only female participants and not applicable to other demographics

Works cited

  1. Nakagawa TH, Moriya ÉTU, Maciel CD, et al. Trunk, pelvis, hip, and knee kinematics, hip strength, and gluteal muscle activation during a single-leg squat in males and females with and without patellofemoral pain syndrome. J Orthop Sports Phys Ther. 2012;42(6):491-501
  2. Kulas AS, Hortobágyi T, DeVita P. Trunk position modulates anterior cruciate ligament forces and strains during a single-leg squat. Clin Biomech. 2012;27(1):16-21.

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