single-leg squat assessment

A guide for trainers: protocol, interventions & clinical implications


Movement and postural assessments are in place as a mean to evaluate the degree of optimal musculoskeletal and neurological force production, through the balanced integrity of the myofascial connections in the kinetic chain (Clark & Lucett, 2010). Postural assessment evaluate sensory-motor control and include static and dynamic assessments; a static, or transitional, postural assessment utilizes a fixed base of support while maintaining one’s constant center of gravity, while dynamic assessments evaluate the movement outside of the base of support (Johnston et al., 2019). Movement assessments also include goniometric and manual muscle testing, which are beyond the scope of this discussion. A prevalent transitional assessment used in athletic and rehabilitative setting is the single-leg squat assessment (SLSA). It is a diagnostic tool which assesses levels of control of the lower limbs in the frontal plane. The SLSA is relevant both to highly athletic populations such as throwers and soccer players, as well as to the recreationally active and rehabilitative individuals, due to its ability to resemble activities of daily living. Through visual feedback and computerized 2D and 3D systems, the practitioner is able to assess main checkpoints in terms of musculoskeletal control; lumbo-pelvic hip complex (LPHC), trunk position relative to the lower limb and the patellofemoral and patellotibial joints ranges of motion (Gianola et al., 2017).


Protocol of SLSA

A basic protocol of SLSA does not require any special equipment and / or monitoring devices. The subject is acquainted with a single leg squat exercise through watching the practitioner performing the task or using video presentations. Verbally, the subject is instructed to:

1. Place hands on hips (for the practitioner, anterior superior iliac spine) and gaze at a stable focal point ahead.

2. Point foot straight forward and maintain neutral LPHC position.

3. Squat down to a comfortable position, refrain from pain if reported. Return back to starting position.

4. Perform up to five repetitions to prevent fatigue-induced posture impairment (Clark & Lucett, 2010).

This video (linked here) and figures 1-2 present the SLSA execution.


Figure 1: SLSA start position


Figure 2: SLSA concentric position

Alternatively, the SLSA can be performed using designated equipment. A known protocol utilizes computerized balance boards, which allow further analysis of balance dynamics (Batty et al., 2019). Visual observation can assess abnormalities and movement impairment through the following main checkpoints; knees, LPHC, trunk and shoulders from an anterior view. Ranges of motion can be measured using software tools such as Dartfish ProSuite 4.5.2.0 video software (Dartfish Software, Alpharetta, GA). A scoring system can be put in place, where a positive score implies more than two-thirds detected abnormalities and a negative score would imply normal kinematics (Ugalde et al., 2015). Lastly, it is important to note that some differences exists in the SLSA protocol; it can be done with the non-stance leg extended backwards, or in line with the ankle or knee flexed forward (Khuu, 2016). Clearly, those changes in stance will affect the observed compensations.


Potential positive findings of SLSA

Movement impairments detected through the SLSA can point out to injury risk factors, mostly in the lower limbs. Such injuries often include an anterior cruciate ligament (ACL) injury, patellar tendinopathy, iliotibial syndrome and sacroiliac joint pain (Gianola et al., 2017). A thorough assessment of the checkpoints throughout the kinetic chain is essential for the identification and selection of future interventions. The kinetic check points, together with possible compensations, include:

· Knees: knee valgus can be detected when (if) the knees move inward. This can be bilateral or unilateral on either limb (figure 3).

· LPHC: SI joint deviations such as hip hike and drop, which are contra-lateral anterior tilts can be observed and related to the non-stance leg position (Khuu et al, 2016). (Figure 4).

· Trunk: inward and outward trunk rotations, which can suggest knee pain as individuals with patellofemoral pain have shown greater trunk lean during the SLSA (Khuu et al., 2016). (Figure 5).



Figure 3: knee valgus in SLSA


Figure 4: hip hike in SLSA


Figure 5: outward torso rotation in SLSA


Soft tissue impairments of the kinetic chain are identified through the SLSA and can set the base for a corrective exercise routine. Muscle imbalances noted in the SLSA repeatedly involve overactive hip adductors of the stance leg and internal obliques (core stability) during trunk rotation; Ipsilateral on inward rotation and contralateral during outward rotation (Clark & Lucett, 2010). Overall, the SLSA is rated as positive when over two-thirds of the kinetic checkpoints are marked as abnormal compensations (Ugalde et al., 2015) and implies a lower level of control in the lower extremities.


Clinical implications of SLSA

The SLSA becomes clinically significant when a practitioner is able to holistically gather kinetic data and apply those into the athlete’s lifestyle. The SLSA is currently used as a pre-cursor for injuries such as ACL and other lower limbs impairments, as well as a “return to activity” screening tool (Batty et al., 2019). The biomechanical background for such clinical implications stems from the lower level of sensory-motor and muscular control of the core and lower extremities during the SLSA; for example, individuals who scored <90 in a limb-asymmetry test during the SLSA were suggested to have poor knee extension mechanism (Batty et al., 2019) whereas noted dynamic knee valgus, more prevalent in females, pointed weakness in the ACL’s surrounding tissues (Ireland et al., 2018). SLSA is clinically applicable to establish a differential diagnosis, assess possible movement impairments and its severity, serve as a continued monitoring method for potential improvements or deteriorations and suggest a course of a future targeted intervention (Baker et al., 2016).


Reliability of SLSA

The clinical relevance of the SLSA is dependent upon its reliability and validity. Two main criteria are measured in studies to determine reliability; inter and intra-related differences between subjects and practitioners, who evaluate and score the SLSA. The literature seems to support a high intra-reliability of the SLSA; repeated assessments by the same practitioner resulted in similar findings, although certain kinetic checkpoints were more reliable than others, such in the case of a hip adduction, pelvic tilt and trunk position (Barker-Davies et al., 2018). Ugalde et al., (2015) reported similar intra-reliability findings; however subjects in the later study had similar characteristics which might increase the intra-reliability of the practitioners in their reported findings. Regarding inter-reliability, or the level of variance between subjects, the SLSA has moderate reliability. Barker-Davies et al. found the same checkpoints to receive a higher inter-reliability score in the SLSA, the hip adduction and trunk position (2018). In a larger field study, 72 subjects were evaluated and inter-reliability was consistent with the literature to be moderate to high (Gianola et al., 2017). The validity of the SLSA has also been assessed and is largely dependent on the methodology, or kinetic checkpoints studied. A cohort study by Batty et al., (2019) found the SLSA to have high validity in identifying knee extensor strength, although the researchers specified its validity to these criteria only. Barker-Davies et al., (2018) reported low validity of the SLSA and recommended that practitioners use additional, repeated testing to increase validity.


Intervention strategies

Movement assessments which are of clinical relevance may suggest future targeted intervention for athletic and recreationally active populations. Interventions such as the continuum of corrective exercise (Clark & Lucett, 2010) can enable return to sport for athletes, improve strength during pre and off season and potentially reduce the risk for injuries. Intervention strategies that are based on the SLSA results will apply to the kinetic checkpoint’s impairment. Inhibition, lengthening, activation and integration exercises are relevant to all movement impairments identified in the SLSA:


* Knee: excessive hip adduction can point out a dynamic knee valgus and over activity of the adductor complex. Interventions can include foam rolling for the adductors, lengthening through static stretch, activation of probable under active glutes and integration through single-leg balance exercises.


· LPHC: pelvic tilts (hip hike and drop) can suggest over activity of the quadratus lumborum and again possible knee valgus (Ugalde et al., 2015). Corrective exercise with additional focus on range of motion such as dorsi and plantar flexion may assist in controlling the valgus and reducing the risk for an ACL injury (Mohammadi et al., 2019).


· Trunk: inward and outward trunk rotations noted in the SLSA can suggest a need for improved core stability; under activity of the internal obliques on the same side of the stance leg when the trunk is rotated outwards can benefit from activation exercises such as a quadruped position with contralateral limb extensions (Clark & Lucett, 2010).


The impaired kinematics at the above checkpoints is related to injuries such as ACL injury, iliotibial band friction syndrome and patellofemoral pain (Gianola et al., 2017). Implementing strategic interventions in the form of corrective exercise, together with otherclinical methods if deem necessary by a medical professional, can improve an existing impairment and have positive acute and some long-term effects of performance and functionality.

References

Baker, R., Esquenazi, A., Benedetti, M. G., & Desloovere, K. (2016). Gait analysis: clinical facts. European Journal of Physical and Rehabilitation Medicine, 52(4), 560-574.


Barker-Davies, R. M., Roberts, A., Bennett, A. N., Fong, D. T., Wheeler, P., & Lewis, M. P. (2018). Single leg squat ratings by clinicians are reliable and predict excessive hip internal rotation moment. Gait & posture, 61, 453-458.


Batty, L. M., Feller, J. A., Hartwig, T., Devitt, B. M., & Webster, K. E. (2019). Single-leg squat performance and its relationship to extensor mechanism strength after anterior cruciate ligament reconstruction. The American Journal of Sports Medicine, 47(14), 3423-3428.


Clark, M., & Lucett, S. (Eds.). (2010). NASM essentials of corrective exercise training. Lippincott Williams & Wilkins.


Gianola, S., Castellini, G., Stucovitz, E., Nardo, A., & Banfi, G. (2017). Single leg squat performance in physically and non-physically active individuals: a cross-sectional study. BMC Musculoskeletal Disorders, 18(1), 1-10.


Ireland, M. L., Bolgla, L. A., & Noehren, B. (2018). Gender differences in core strength and lower extremity function during static and dynamic single-leg squat tests. In ACL Injuries in the Female Athlete (pp. 239-257). Springer, Berlin, Heidelberg.


Johnston, W., O’Reilly, M., Argent, R., & Caulfield, B. (2019). Reliability, validity and utility of inertial sensor systems for postural control assessment in sport science and medicine applications: a systematic review. Sports Medicine, 49(5), 783-818.


Khuu, A., Foch, E., & Lewis, C. L. (2016). Not all single leg squats are equal: a biomechanical comparison of three variations. International Journal of Sports Physical Therapy, 11(2), 201.


Mohammadi, H., Daneshmandi, H., & Alizadeh, M. H. (2019). Effect of Corrective Exercises Program on Strength، ROM, and Performance in Basketball Players with Dynamic Knee Valgus. Scientific Journal of Rehabiliation Medicine, 8(3), 29-41.


Ugalde, V., Brockman, C., Bailowitz, Z., & Pollard, C. D. (2015). Single leg squat test and its relationship to dynamic knee valgus and injury risk screening. PM&R, 7(3), 229-235.