Tibialis Anterior Activity During Squats

Question:

Why do a good 60 percent of my clients feel work being done in the tibialis anterior region when I'm teaching them to squat, only for it to go completely away after the first couple of times?

Answer:

During squatting exercises, a number of muscles are activated in either an eccentric, isometric or concentric action. When examining the squat, most trainers are interested in the primary movers - the quadriceps femoris, which is made up of the vastus lateralis, vastus intermedius, rectus femoris and vastus medialis. Although the quadriceps musculature is emphasized during the squat, a number of other muscles are activated to provide stabilization at the hip, knee and ankle joint. In the hip region, the gluteus medius and maximus are primarily activated. At the knee, coactivation of the “hamstring” group (biceps femoris, semitendinosus and semimembanosus) is required for stabilization and neuromuscular control. As we move down the leg to the ankle, we see activation on both the posterior (gastrocnemius –medial and lateral head, soleus, flexor digitorumlongus and flexor halucis) and anterior side (tibialis anterior, extensor digitorum longus and fibularis liongus). In addition to the musculature that is being activated, a number of ligaments and tendons are put under stress as well. A few noteworthy ones would include the patellar tendon, fascia lata, anterior and medial cruciate ligament and the tendon of the fibularis longus.

It is apparent that a multitude of actions and forces are occurring during the squat, but how does this relate to a feeling of activation or discomfort in the tibialis anterior region? During the squat movement, a great deal of shear forces are applied to the knee. These sheer stresses can cause the knee to move in a medial or lateral direction when an imbalance is present. This in turn can cause a radiant affect on the ankle joint. To stabilize the foot and ankle during the squat, the anterior region of the lower leg is activated. The tibialis anterior is of importance in this stabilization, but the fibularis longus may be more related to the initial feelings of activation as the fibularis longus lies underneath the tibialis anterior. In addition, the tendon wraps underneath the foot connecting to the base of the first metatarsal. Therefore, whenever there is inversion or eversion, there will be some activation of the musculature in the tibialis anterior region.

The second part of the question asks, why does this sensation go away after a couple of training sessions? A main mechanism that could reduce or eliminate the sensation of tibialis activity could be related to the muscle lengthening due to stretch. In a recent article by de Weijer et al., they examined the effect of static stretch and warm-up activities on muscle lengthening over a short period of time. Briefly, subjects were assigned to one of four groups: (1) warm-up and static stretch, (2) static stretch only, (3) warm-up only and (4) control. The warm-up was 10 minutes of stair climbing at 70 percent of maximum heart rate. Static stretch consisted of a single session of three 30-second passive stretches of the hamstring. Hamstring length was measured preintervention and at immediately 15 minutes, 60 minutes, four hours and 24 hours after stretching. At 24 hours post stretch, the warm-up-and-static-stretch group had an average increase of 10.3 degrees and 7.7 degrees, respectively. Control and warm-up-only groups showed no significant increase in hamstring length between preintervention and any of the post intervention measurements. A significant increase in hamstring length can be maintained for up to 24 hours when using static stretching. Muscle length gains are greatest immediately after stretching and decline within 15 minutes.

The significance of this study demonstrates that there are rapid adaptations to stretching activities that are relatively long lasting. Since squatting activities increase tibial sheer stress, pre stretching of the hamstring may lead to reduced stress in the anterior tibialis region. Furthermore, we could speculate there may be a potential stretching effect on the fibularis longus, which may also reduce or eliminate the sensations felt in this area. It would therefore be prudent to provide some flexibility training for your clients prior to engaging in a squatting routine. 

References:

1. Delavier, F. (2001). Strength training anatomy. Human Kinetics: Champaign, IL.
2. De Weijer, V.C., Gorniak, G.C. and Shamus, E. (2003). The effect of static stretch and warm-up exercise on hamstring length over the course of 24 hours. J Orthop Sports Phys Ther. 33:727-733.
3. Shields, R.K., Madhavan, S., Gregg, E., Leitch, J., Petersen, B., Salata, S. and Wallerich, S. (2005). Neuromuscular control of the knee during a resisted single-limb squat exercise. Am J Sports Med. 33:1520-1526.