The foot arch is a remarkable structure that provides the foundation for all human movement, acting as a spring, a shock absorber, and a rigid lever. This curved configuration supports the entire body’s weight. Maintaining the health of this structure is important for overall mobility, influencing everything from standing posture to running mechanics. A functional arch system manages the forces exerted on the feet, ensuring they are distributed efficiently throughout the lower limbs.
Defining the Healthy Arch
A well-functioning arch is defined less by a specific height and more by its resilience and ability to change shape under load. The most prominent structure is the Medial Longitudinal Arch (MLA), which runs along the inner border of the foot from the heel to the ball of the foot. This arch is formed by a sequence of bones, including the calcaneus, talus, navicular, cuneiforms, and the first three metatarsals. The talus bone sits at the peak, acting like the keystone of a bridge, which is held in place by surrounding bones, ligaments, and tendons.
When viewed from the side, a healthy MLA displays a noticeable curve, creating a space between the ground and the midfoot when standing. The arch is not a static bone structure but a complex system supported passively by strong ligaments, like the plantar fascia, and dynamically by muscles and tendons. This combination allows the structure to flatten slightly when bearing weight and restore its curvature when the weight is removed.
The Essential Functions of the Arch
The unique architecture of the foot arch enables two primary biomechanical roles necessary for efficient movement. The first function is shock absorption, where the arch acts like a natural suspension system for the body. Upon heel strike during walking or running, the arch flattens and lengthens slightly, a movement that helps to dampen the impact forces traveling up the leg. This controlled collapse stores mechanical energy in the stretched tendons and ligaments.
The second essential function is weight distribution and propulsion, which transforms the foot from a flexible shock absorber to a stiff lever. As the body moves forward over the foot, the arch re-supinates, becoming more rigid for the push-off phase of the gait cycle. This stiffening allows the foot to efficiently transfer power from the calf muscles to propel the body off the ground. A functional arch system ensures that body weight is distributed proportionally across the heel and the ball of the foot, reducing excessive strain on any single area.
Common Arch Variations and Their Implications
While there is an ideal range, arch health exists on a spectrum, and arch height alone does not determine function. The two main variations from the average, or medium, arch are low arches (often called flat feet or pes planus) and high arches (pes cavus). Low arches are characterized by a reduced or absent curve, where the sole of the foot may make nearly complete contact with the ground. High arches are characterized by an exaggerated curve, leaving a very small contact area between the ground and the midfoot.
The most important distinction is whether a variation is flexible or rigid, as this affects its functional implications. A flexible arch, whether low or high, changes shape when the foot is non-weight-bearing, indicating that the arch’s supportive structures are still somewhat pliable. A low arch that is flexible, for instance, may appear when standing but reform when sitting or standing on the toes, often causing no symptoms. A rigid arch, however, maintains its shape regardless of whether the foot is bearing weight, often leading to pain and instability. A rigid low arch struggles to become a rigid lever for propulsion, while a rigid high arch is poor at shock absorption, placing excessive pressure on the heel and forefoot.
A simple assessment is the “wet test,” where a footprint is compared while standing versus when the arch is lifted, providing a basic visual cue to the arch’s flexibility. Ultimately, a “good arch” is a functional one that can adapt to forces and terrain without causing pain or dysfunction.