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Tuesday, June 6, 2023

Motor Recruitment and Compensation During a Single Leg Squat

Brent Brookbush

Brent Brookbush


Research Review: Motor recruitment and compensation during a single leg squat.

By Jinny McGivern, DPT, PT, CFMT, Certified Yoga Instructor

Edited by Brent Brookbush DPT, PT, COMT, MS, PES, CES, CSCS, H/FS

Original Citation: Mauntel, T., Begalle, R., Cram, T., Frank, B., Hirth, C., Blackburn, T., & Padua, D. (2013). The effects of lower extremity muscle activation and passive range of motion on single leg squat performance. Journal Of Strength And Conditioning Research / National Strength & Conditioning Association, 27(7), 1813-1823. ABSTRACT

Why is this relevant?: This study provides essential information about how the relationship between lower extremity range of motion and muscle activation patterns relate to the incidence of dynamic knee valgus during a single leg squat. The single leg squat is a movement pattern that is common to many functional & recreation activities. An increase in dynamic knee valgus has been associated with lower extremity injuries such as ACL rupture, MCL rupture and Patellofemoral Pain Syndrome. Characteristics of an optimal movement pattern are identified and provide the human movement professional with a basis for designing intervention strategies to improve movement and reduce the risk of future injury.

Caption: single-leg-squat-to-bilateral-cable-pull-down

Study Summary

Study DesignCohort Design
Level of Evidence 2b - Individual Cohort Study
Subject Demographics
  • Age: 20.2 +/- 1.5 yrs (Experimental - Increased knee valgus in SLS); 20.2 +/- 1.8 yrs (Controls - Neutral knee alignment in SLS)
  • Gender: 20 males; 20 females
  • Characteristics: young; healthy; physically active; no low back or lower extremity injury in previous 6 months; no known neurological condition; no pregnancy
  • No significant differences in height, weight or minutes of physical activity per week between groups
Outcome MeasuresSubjects were assigned to the control group or medial knee displacement (MKD) group based on observation of movement of knee in SLS.  MKD was defined as movement of the midpoint of the patella medial to the great toe during SLS in at least 3/5 trials. Passive range of motion (PROM) for the following 10 lower extremity (LE) motions: Hip external rotators, Hip internal rotators, Femoral anteversion, Iliotibial band, Hip adductors, Iliopsoas, Hamstrings, Dorsiflexion (knee straight), Dorsiflexion (knee flexed), Posterior Talar glide. Normalized Surface EMG LE muscle activity for: Gluteus Maximus, Gluteus Medius, Hip Adductors, Medial Hamstrings, Biceps Femoris, Vastus Medialis, Vastus Lateralis, Medial Gastrocnemius (Normalized to max voluntary isometric contraction).EMG Co-activation Ratios for:  Gluteus Medius: Hip Adductors & Gluteus Maximus: Hip Adductors.  Ratios of 1.0 indicate equal activation of both muscle groups; Ratios greater than 1.0 indicate greater activation of respective gluteal muscles as compared to adductors.
  • There were no significant differences between groups for MVIC (normalized by subject weight) for any of 6 muscle groups tested (hip extensors, hip abductors, hip adductors, hamstrings, quadriceps, plantar flexors).
  •  No significant differences between the 2 groups in normalized EMG amplitude for any of the 11 muscles tested during the SLS task.
  • Significant differences between both co-activation ratios between groups.  The MKD group had significantly smaller ratios than controls for both gluteal muscles.  This indicates that that those in the MKD group had greater activation of adductors with respect to both gluteus medius & maximus than controls during SLS.
  • No significant differences between groups were observed for PROM with the exception of: ankle dorsiflexion knee straight (less than controls), dorsiflexion knee bent (less than controls), posterior glide of talus (greater than controls).
ConclusionsThese results indicate that altered neuromuscular activation of hip adductors & gluteals, combined with decreased ankle dorsiflexion ROM may contribute to a dynamic knee valgus during a single leg squat.  The results of this study demonstrate that comparisons of EMG activity of different muscles may not provide enough information to understand differences between those with and without MKD in SLS.  Co-activation ratios which explore the relationships between muscles revealed greater differences between groups.  Restrictions in gastrocnemius & solues, not the talo-crural joint, are implicated as the cause of restricted dorsiflexion because of the greater amount of posterior talar glide observed in those with MKD.  A decreased amount of posterior talar glide would implicate abnormal joint arthokinematics because posterior glide is the accessory motion associated with ankle dorsiflexion.
Conclusions of the ResearchersDecreased dorsiflexion resulting in increased pronation & tibial internal rotation may increase femoral adduction/internal rotation leading to MKD during dynamic tasks such as SLS. It is possible that the changes in neuromuscular activation of the hip musculature is in response to changes in afferent input as the body attempts to compensate for decreased sagittal plane motion at the ankle with motion in the transverse & frontal planes.

Single Leg Touch Down with Posterior Pull

Review & Commentary:

The authors of this study took excellent care to establish specificity in their selection of subjects. Subjects were excluded if they met any 1 of the 3 following criteria: they demonstrated knee varus, had inconsistent MKD, or if upon returning for the testing session no longer clearly fit into assigned group. There was a clear definition of the criteria for inclusion in the MKD versus control group. This allows the reader to have a clear understanding of the characteristics of the individuals examined in this study. With similar attention to detail, the SLS task was standardized using uniform positioning of the head, gaze, upper extremity & non stance lower extremity, as well as markers for target depth of squat & a metronome for standardization of rate of performance of the task. Multiple trials were performed and averaged for each outcome measure providing greater accuracy of measurement. The researchers elected to examine more than just the isolated activity of individual muscles through their use of co-activation ratios, and they were able to gain understanding of how the relationships between muscles impact movement.

This study had a relatively small, homogenous sample of young, active, healthy individuals, therefore the results may not be able to be generalized to a sedentary, older or injured population. This study is unable to comment on the effect of degenerative or aging processes on the occurrence of dynamic knee valgus, however it is valuable in providing information on the movement patterns related to non-traumatic knee injuries in a young active population. The researchers utilized surface EMG, which is more susceptible to cross talk from other muscles than needle EMG. The researchers did take precautions to minimize this interference through the use of previously researched standard placements of electrodes confirmed with active muscle contractions. In terms of muscles selected for EMG analysis, there was asymmetry in the observation of activity of the gastrocnemius . The medial gastrocnemius was included because it has been hypothesized to resist knee valgus. It would have been helpful if the lateral gastrocnemius had been included as well to observe if it's activity was significantly different from that of the medial head. It is possible that the lateral gastrocnemius might have a role to play in increasing knee valgus and analysis of an activation ratio between the 2 parts of this muscle would provide useful information. With respect to measurement, it may have been more specific to the task of the SLS to measure dorsiflexion using a closed kinetic chain method as opposed to the open chain method used in this study. Finally the authors state that the posterior talar glide test may not be the most sensitive measure of talar mobility due to its lack of association with measures of ankle dorsiflexion range of motion measures. Further research should examine additional 3-D kinematics of the lower leg & foot to provide more information about this segment during the SLS task.

Why is this study important?

This research demonstrates the relationships between multiple parts of the lower extremity kinetic chain and how they may impact each other through altered afferent input and abnormal biomechanics. This study emphasizes how important it is to not just examine the activity of different individual muscles during an activity, but also looks at the relationships between groups of muscles and how these impact movement. Balancing muscle activity around a joint does not mean encouraging equal activation of muscles on both sides of it, but rather fostering optimal activation of each group. In the case of this study, those without a dynamic knee valgus in the single leg squat (a more optimal movement pattern) demonstrate increased activation of the gluteus medius & gluteus maximus , and decreased activation of the adductors .

How does it affect practice?

When research establishes that there is a connection between multiple joints and muscles in determining a movement pattern, it is essential that the human movement professional develop a comprehensive intervention strategy for the entire lower extremity rather than for a single joint in the chain.

How does it relate to Brookbush Institute Content?

This research supports the Brookbush Institute's exercise selection strategies, which encourage the human movement professional to consider techniques that address all affected structures in a dysfunctional pattern including short over-active muscles, long under-active muscles, as well as, addressing joint restrictions when creating a corrective exercise strategy. Further, the demonstration of compensation patterns supports the assertion that dysfunction, regardless of the source of an individual's chief complaint, will affect multiple joints and muscles. Implementation of an integrated strategy to address all affected structures will result in improved balance between muscles and better joint mechanics. Further research will be needed to test the efficacy of this intervention strategy immediately post-treatment, as well as, carry-over between sessions, and long-term outcomes. This article specifically relates to the abnormal movement patterns observed in the Lower Leg Dysfunction (LLD) model. This model outlines how limited dorsiflexion impacts motion at both the knees & the hips. The videos below demonstrate some sample techniques used to improve some of the implied dysfunction in this research study. The Overhead Squat Assessment can be used to identify Lower Leg Dysfunction.

Calf Static Release:

Adductor Release:

Self-administered Ankle Mobilization:

Slant Board Calf Stretch

Standing Adductor Stretch:

Tibialis Anterior Activation:

Gluteus Medius Activation Progression:

Resisted Single Leg Balance

© 2014 Brent Brookbush

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