Knee valgus, commonly referred to as medial knee displacement, is commonly thought to occur when reduced gluteal activity (maximus and medius) allows for a greater degree of hip internal rotation which leads to tibial rotation and hence knee valgus. While most think knee valgus is caused by lack of strength in the gluteus maximus and medius, a recent research study shows that this may not be the case. Instead, the study suggests lower leg muscles may be responsible for knee valgus.
In this study Padua, Bell, and Clark (2012) set out to discover two things:
The subjects for this study were 30 women and 7 men who did not display any lower leg injuries. The subjects were assigned either to a control group or valgus group. The control group included 19 subjects who displayed no knee valgus during a squat movement and where the knee remained over the toes in the frontal plane. The valgus group, as the name implies, included 18 subjects whose patella moved medially (knee valgus) during the squat movement.
During the trials, the researcher used EMG to measure the activity of the gluteus maximus, gluteus medius, adductor magnus, medial gastrocnemius, lateral gastrocnemius, and tibialis anterior. Lower body movement was measured using an electromagnetic motion-analysis system.
The first trial consisted of the subjects doing 5 double legged overhead squat reps, barefoot, feet shoulder-width apart, and toes pointed straight ahead. Subjects were instructed to squat to 80 degrees of hip flexion. After the first trial was complete a second trial was conducted using the same protocol with the addition of a 2-inch heel lift (wooden block placed under the feet).
After analyzing the results, the researcher found no difference in gluteal activation between the control and valgus group. However, the valgus group had a 34% greater increase in adductor activity than the control group. Additionally, no differences in EMG activity were seen in the hip muscles with and without the heel lift.
Upon further analysis, the researchers discovered the valgus group displayed greater EMG activity of the tibialis anterior compared to the control group with and without the heel lift. Additionally, EMG activity in the valgus group when using the heel lift was less when not using it compared to the control group. Furthermore, the researchers found that medial and lateral gastrocnemius activity was greater in the valgus group compared to control in the descending phase of the squat without the heel lift. They also noted that medial and lateral gastrocnemius activity was greater in the valgus group with the heel lift than without it. This was not noted in the control group.
As we delve deeper into the study the results showed that the valgus group displayed greater knee valgus without a heel lift compared to the control group. With the addition of a heel lift to the valgus group, medial displacement of the knee was less. In the control group, there was no effect on frontal knee displacement when using the heel lift.
The researchers concluded gastrocnemius, tibialis anterior, and adductor EMG activity levels were higher in those that displayed knee valgus compared to those who did not. More importantly, they found no differences in EMG activity levels in the gluteal muscles in subjects with and without knee valgus.
The researchers further suggested that the increase in gastrocnemius activity may have caused greater plantar-flexion moments at the ankle and in turn increased ankle dorsiflexion stiffness. Increases in anterior tibialis activity was also suggested to cause ankle dorsiflexion stiffness. Therefore, the researchers proposed that ankle dorsiflexion stiffness/restricted dorsiflexion ROM leads to pronation of the foot which increases tibial internal rotation and ultimately leading to knee valgus.
Based on the above research a person with an extremely flat foot may be more predisposed to excessive knee valgus due to the greater degree of pronation that usually occurs with this anatomical dysfunction.
Padua, D. A., Bell, D. R., & Clark, M. A. (2012). Neuromuscular characteristics of individuals displaying excessive medial knee displacement. Journal of athletic training, 47(5), 525-536.