Sole of the foot

The sole is the entire ground-contacting surface of the foot. It is often divided, from back to front, into the heel, the foot arch in the middle, and the ball of the foot just behind the toes. When you stand, your weight is distributed across these three regions. When you walk, the heel contacts the ground first, then your weight shifts forward, and finally the ball of the foot and big toe push off the ground.

In the middle of the sole, the strong plantar fascia fans out from the heel toward the toes. This thick fibrous sheet supports the arch from below, with layers of small muscles above it. The skin is also among the thickest on the body, and a fatty cushion provides another layer of impact absorption during walking. The sole also has many sensory nerves that detect pressure and the texture of the ground, playing a major role in maintaining balance even with your eyes closed. The nerves supplying the sole divide into branches serving the inner and outer sides; see Medial plantar nerve and Lateral plantar nerve for more details.

The foot is a distinctive structure whose properties change depending on the situation.

• As it contacts the ground, the joints within the foot loosen, allowing it to absorb impact flexibly.
• As it pushes off the ground, it instead becomes a rigid lever that transfers force forward.

The windlass mechanism is involved in this transition. When the big toe bends upward, the plantar fascia tightens like a rope winding around a pulley. This tension draws the heel and metatarsal bones toward each other, raising the arch and stiffening the foot. Described by Hicks in 1954, this mechanism is notable because it occurs automatically when the toes are lifted, without requiring separate muscle activation. This is why you can feel your arch rise when you stand on tiptoe.

The “foot core” perspective has recently been introduced as a way of viewing the foot as a single functional unit. It brings together passive structures such as bones, ligaments, and the plantar fascia; the intrinsic foot muscles, the small muscles within the foot; the extrinsic muscles that extend down from the ankle; and the nervous system. The idea is that, just as the trunk’s core supports the spine, the intrinsic foot muscles provide local support for the arch. See Foot core paradigm for more details.

• Standing all day or walking on hard surfaces can leave the soles aching or burning. Some people also feel a pulling sensation in the heel with their first steps in the morning.
• When you walk for a long time barefoot or in shoes with thin cushioning, the ball of the foot tires first.
• Differences in arch shape, such as flat feet or pes cavus, change where weight is borne, so the areas of the sole that feel tired also differ.
• Areas where particularly thick calluses develop on the sole show where you usually bear more weight.

• Sole massage — While seated, place a tennis ball or small ball under your sole and slowly roll it. Pause briefly over achy areas and apply a comfortable amount of pressure.
• Toe exercises — Spreading and curling your toes, or pulling a towel toward you with your toes, activates the intrinsic foot muscles.
• Heel raises — Hold onto a wall and slowly raise and lower your heels to feel the arch rise through the windlass mechanism.
• Choosing shoes — Shoes with plenty of room across the forefoot and cushioning are comfortable for prolonged standing. See also Shoe cushioning and Forefoot width and toe box.
• Barefoot time — Walking barefoot for short periods at home is another way to awaken sensation in the soles. Rather than doing it for a long time at once, gradually increase the duration.

• Heel pain with your first steps in the morning that continues for several days may resemble the pattern of plantar fasciitis.
• Persistent tingling or reduced sensation in the sole
• Persistent pain in the sole of only one foot, or swelling accompanied by warmth in that sole

In these situations, having the structure of your foot and your walking pattern assessed at an orthopedics or rehabilitation medicine clinic can help.