Home > Injury Prevention, Knee Injury, Movement Dysfunction > Neuromuscular characteristics associated with knee valgus collapse during an overhead squat

Neuromuscular characteristics associated with knee valgus collapse during an overhead squat

Padua DA, Bell DR, Clark MA.  Neuromuscular characteristics of individuals displaying excessive medial knee displacement.  Journal of Athletic Training 47(5):525-536, 2012.

http://www.ncbi.nlm.nih.gov/pubmed/23068590

What issue was addressed in the study, and why?

Knee valgus motion is frequently hypothesized as a risk factor for multiple lower extremity injuries.  An aim of many exercise programs is to correct for excessive knee valgus motion through a variety of mobility, stability, and strengthening techniques.  The successful correction of knee valgus motion requires an understanding of the underlying neuromuscular characteristics associated with it.  Multiple theories have been proposed to explain the muscle imbalances associated with knee valgus motion; however, there is little scientific evidence to support these theories.  Identifying differences in muscle activation patterns between those who do and do not display knee valgus collapse is an initial step to validating the muscle imbalances associated with this movement dysfunction.  Therefore, the purpose of this study was to compare hip and ankle muscle activation amplitude in those with and without visual presence of knee valgus motion (medial knee displacement) during an double leg (overhead) squat task.

Who were the participants in the study?

A total of 37 participants volunteered for this study and were separated into two groups based on the presence of medial knee displacement during an double leg squat task.  The control group (CON, n=19) did not demonstrate medial knee displacement.  The medial knee displacement group (MKD, n=18) were observed to have their patella move medial to their great toe during the double leg squat, but not once a 2-inch lift was positioned under their heels.  Individuals who displayed MKD during both no-heel lift and heel-lift conditions were excluded from the study.

This was done as there are different muscle imbalances believed to be associated with knee valgus motion during no-heel-lift and heel-lift conditions.  MKD that is displayed during the no-heel-lift condition, but not during the heel-lift condition is believed to be associated with ankle muscle imbalances.  MKD that is displayed during both no-heel-lift and heel-lift conditions is thought to represent a hip muscle imbalance.  Thus, this study focused on identifying the presence of ankle muscle imbalances given the inclusion criteria.

What did the researchers do for this study?

Surface EMG electrodes were used to record the activation amplitude from the medial gastrocnemius, lateral gastrocnemius, tibialis anterior, adductor magnus, gluteus medius, and gluteus maximus muscles.  An electromagnetic motion analysis system was used to quantify medial knee displacement motion.  All variables were measured during two different double leg squat tasks performed at a controlled movement velocity and squat depth.  Subjects performed the double leg squat task during both no-heel-lift and heel-lift (2-inch) conditions.  During all double leg squat trials the individuals were instructed to keep their heels on the floor and maintain their toes pointing straight ahead.

What new information was learned from this study?

There was no difference between the CON and MKD groups for gluteus medius and gluteus maximus activation amplitude during both the no-heel-lift and heel-lift double leg squat tasks.  However, the MKD group demonstrated 34% greater activation of the adductor magnus muscle compared to the CON group.

The MKD group demonstrated greater gastrocnemius (40% greater) and tibialis anterior (25% greater) muscle activation amplitude compared to the CON group during both double leg squat tasks.

What are the clinical applications of this study?

Presence of MKD that is corrected with heel-lifts is associated with increased gastrocnemius, tibialis anterior, and adductor magnus muscle activation amplitude.  However, there was no difference in gluteal muscle activation amplitude between MKD and CON participants.  Thus, there appears to be 2 neuromuscular strategies associated with knee valgus motion.  Increased gastrocnemius and tibialis anterior activation likely increases ankle joint stiffness, thus limits the available dorsiflexion range of motion during functional tasks, which is theorized to lead to compensatory knee valgus motion.  Increased adductor magnus activation can lead to an imbalance between the gluteals and adductor muscles, resulting in a net hip adduction moment during the squat task.  In fact, the MKD participants in the current study demonstrated 4 times greater adductor magnus activation compared to their gluteal muscles, which indicates a significant muscle imbalance between these muscle groups.  This would ultimately result in the visual presence of knee valgus motion as the femur moved medially during the squat task.

Interventions aimed at inhibiting and lengthening the gastrocnemius, tibialis anterior, and adductor magnus muscles may be necessary components of exercise interventions aimed at correcting knee valgus motion.

What are the limitations of the study, and what areas should be considered for future research?

All of the participants were healthy at the time of testing.  Thus, these findings are limited to healthy individuals and it is possible that different muscle activation patterns may exist in those who display knee valgus motion and are symptomatic.  Future research is needed to confirm the presence of ankle muscle imbalances (increased gastrocnemius and tibialis anterior activation) and synergistic dominance of the adductor magnus (increased adductor magnus activation) in those with MKD who are also symptomatic.

The findings from this study are part of a larger study whose findings were previously published in the following article:

http://www.ncbi.nlm.nih.gov/pubmed/18586134

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