In this final exercise, we will investigate the leg, the dorsum of the foot and the sole of the foot.

The leg must bear the weight of the entire body and effectively deliver the forces of gravity and propulsion to the foot. It also is the origin for the powerful muscles that run to the ankle and foot. These muscles maintain balance and drive us forward.

The toes are not prehensile tools therefore, the function of the leg muscles primarily affects the ankle, and not the toes. The foot maintains balance with remarkably little muscular effort, yet is mobile enough to act as a lever during forward motion.

Figure 16-1
Major structures of the leg shown in a cross section at a level approximately 3 inches below the patella.

These functional demands mandate the foot be designed like an arch - a flexible arch. This arch design spreads our body weight out over a large area across our foot, which simultaneously provides a more stable base for our precarious bipedal posture. It also allows propulsive forces to be effectively delivered to the ground time after time, without damage to the foot itself.

The foundation of the arch of the foot is provided by the shape of the bones which form an inferior concavity or longitudinal arch when they are articulated one with another.

The talus bone forms the "keystone" or center, upper most stone in this arch. It is a key component in maintaining the arch shape. Ligaments and muscles also play an important role in arch maintenance.

While working with the leg and foot, compare the similarities and differences with the forearm and hand. Some similarities are listed here:

• Both the leg and the forearm have two bones.
• Larger, more powerful muscles that move the foot and hand are located in the leg and forearm respectively.
• Both foot and hand have palmer/plantar surfaces which come into contact with objects of interest such as the ground and food.
• Muscles found within both the foot and hand (intrinsics) are very similar in design, not to mention in name.