The human body utilizes various systems to direct forces in and through weight-bearing structures during movement. These systems mechanically redirect and absorb impact, adjust for dynamic and uneven surfaces, and maintain a stable base of support. To maximize function, suspension systems in the foot, knee, pelvis, and spine balance optimal directional rigidity with joint mobility to accurately transfer kinetic energy through the kinematic chain.
Focusing on the foot and ankle, this complex structure must adapt and adjust, providing static support when standing and dynamic management of ground contact during upright movement. While there are some parallels between the architecture of the human hand and foot, there is also significant variation due to the weight-bearing nature of the lower extremity. Greater rigidity and stability is required of the foot in order to manage interactions between the full weight of the body and the ground.

Foot Mechanics During Gait
A single gait cycle begins as the lead leg swings forward and the heel makes contact with the ground. A dense pad of springy connective tissue on the heel allows elastic deformation, distributing forces evenly up through the dense calcaneus bone as the full weight of the body shifts over the lead foot. Moving through the stance phase, weight shifts from the calcaneus to the tarsal bones as the trail leg begins to swing forward. Mobility in the transverse tarsal joint, a functional unit made up of the calcaneocuboid and talonavicular joints, provides optimal weight shift through the tarsals and to the metatarsal bones while simultaneously accommodating uneven ground surface contact.
The five metatarsal bones must be in optimal alignment and orientation to direct forces efficiently from the heel to the ball of the foot. A complex network of ligaments ensures minimal foot splaying and assists the dynamic stabilizers as they maintain the architecture of the longitudinal arch during weight transfer. Deep leg muscles such as the posterior tibialis play a critical role in stabilizing and directing force transfer at this point in the gait cycle.
The integrity of the transverse arch becomes significant as the heel begins to lift and the full weight of the body moves onto the ball of the foot. This structure, formed by connective tissue joining the metatarsal heads together, is visible when the foot is nonweight-bearing. When weight-bearing, the connected heads further resist splaying and allow the ball of the foot to function as a stable unit. As the weight rolls over the ball of the foot, acceleration can be modified to accurately coordinate movement of the ankle with the motion of the opposing lower extremity. This modification and adjustment of acceleration is critical to proper mechanics during the fall-and-catch phases of human gait.
During push-off, or the end phase of gait, weight is shifted from lateral to medial across the ball of the foot. Strong muscles associated with the great toe provide the final thrust for perpetuating forward momentum. Once this is complete, the cycle begins again with the opposite leg.

Dysfunction
Proper foot mechanics rely on an optimal balance between rigidity and mobility, as well as specific directionality and timing of force transfer. Too much or too little mobility at the transverse tarsal joint, also known as excessive pronation or supination, can lead to dysfunction in the entire kinematic chain. Additionally, longitudinal or transverse arches that are either too supple or too rigid may lead to similar mechanical issues. These may present as foot, ankle, knee, hip, or even low-back pain that worsens with prolonged standing, walking, or running.

Christy Cael is a licensed massage therapist and certified strength and conditioning specialist. Her private practice focuses on injury treatment, biomechanical analysis, craniosacral therapy, and massage for clients with neurological issues. She is the author of Functional Anatomy: Musculoskeletal Anatomy, Kinesiology, and Palpation for Manual Therapists (Lippincott Williams & Wilkins, 2009). Contact her at christy_cael@hotmail.com.