Exploring tibialis anterior and fibularis longus: the leg stirrup
In this article, we’ll explore two muscles found in the leg: tibialis anterior and fibularis longus. These two muscles are both important for walking, jogging, and running, as well as jumping and kicking. Keep reading to learn more about their attachments and actions.
Where are the tibialis anterior and fibularis longus?
Generally, you’ll find these two muscles in the leg. Tibialis anterior is an important muscle in the anterior compartment, the front of the leg. You’ll find fibularis longus in the lateral compartment, or the outside of the leg.
Muscle attachments
Specifically, tibialis anterior's origin, or proximal attachment, is on the lateral shaft of the upper ⅔ of the tibia (larger of the two lower leg bones) and the lateral condyle of the tibia. Distally, it attaches onto the medial cuneiform and the base of the first metatarsal.
Fibularis longus attaches proximally to the lateral shaft of the upper ⅔ of the fibula (smaller of the two lower leg bones) and the head of the fibula. Distally, it attaches to the medial cuneiform and the base of the first metatarsal. It meets the distal attachment of tibialis anterior there.
Muscle actions
These two muscles do opposite actions. Specifically, tibialis anterior does dorsiflexion and inversion of the foot at the ankle. And if the foot is in a fixed position, like when we’re standing on it, tibialis anterior helps to pull our body over our foot. In contrast, fibularis longus does plantarflexion and eversion of the foot at the ankle. What’s as important as naming the individual actions of these two muscles, is how they work together.
Muscular dynamics
These two muscles work together to form the stirrup of the foot. That means they work together to manage the balance between eversion and inversion of our foot. Particularly when we’re walking over uneven surfaces, these two muscles work together to stabilize the ankle joint.
Remember that what we refer to as the ankle joint is really more than one bone-to-bone connection. The tibiotalar joint (also called the talocrural joint) is where the distal end of the tibia (the larger of the two lower leg bones) meets the talus bone. The talus bone is the bone that sits between the distal end of the tibia and the calcaneus (heel bone). The talocalcaneal joint (also called the subtalar joint) is where the talus bone meets the calcaneus.
The gait cycle
Along with the other muscles of the leg, ankle, and foot, these two muscles both play an important role in our gait cycle. Our gait cycle starts when the heel of one foot hits the ground and we roll through the foot as the bottom of the foot makes full contact with the ground. (When our foot is on the ground it’s called the stance phase.)
When we roll through our foot, however, we don’t roll straight back to forward. There is actually a small amount of inversion followed by eversion of our ankle. Both the tibialis anterior and fibularis longus help control this shift in motion. As we’re lowering our foot to the ground, tibialis anterior is eccentrically contracted, helping us to lower our foot in a controlled way. When our foot is on the ground, it helps stabilize our ankle joint and assists with pulling our body over our foot.
As we get ready to take our next step, we shift our weight forward over the toes of that foot. When we press our toes to the ground to pick up our foot, the tibialis anterior does dorsiflexion of the ankle. (When our foot is in the air it’s called the swing phase.) That dorsiflexion, while our foot is in the air, helps keep us from stubbing our toes on the ground as we swing our foot through and place it back on the ground, completing our step.
References
Chaitow, L. and J. DeLany. 2011. Chapter 14: The Leg and Foot. In Clinical Application of Neuromuscular Techniques. Volume 2 - The Lower Body (Second Edition).
Travell, J.G. and D.G. Simons. 1993. Chapter 19: Tibialis Anterior Muscle and Chapter 20: Peroneal Muscles. In Myofascial Pain and Dysfunction—The Trigger Point Manual. Volume 2.
