The Arch, the Windlass and the Flexible-to-Rigid Lever
- The foot divides into HINDFOOT (talus, calcaneus), MIDFOOT (navicular, cuboid, three cuneiforms) and FOREFOOT (metatarsals, phalanges), joined at the CHOPART and LISFRANC joints, and is arranged into medial and lateral longitudinal arches and a transverse arch.
- Arch support comes in three layers: BONY (the talar head/navicular keystone), LIGAMENTOUS (plantar fascia, SPRING ligament, long and short plantar ligaments) and MUSCULAR (tibialis posterior above all).
- WINDLASS: MTP dorsiflexion, the hallux most of all, winds the plantar fascia round the metatarsal heads, raising the arch and inverting the hindfoot into a rigid lever; JACK'S (Hubscher) test demonstrates it.
- The fascia is also an ARCH-SPRING, stretching in early-mid stance and recoiling at push-off; it is not perfectly isometric but acts as a near-isometric windlass in propulsion.
- Subtalar PRONATION at heel strike makes the transverse tarsal axes PARALLEL and unlocks the midfoot; SUPINATION in terminal stance makes them NON-PARALLEL and locks it.
- Gait is ~60% STANCE and ~40% SWING, advancing over the heel, ankle and forefoot ROCKERS.
- “Arch supports in 3 layers: bony (keystone = talar head/navicular), ligamentous (plantar fascia, SPRING ligament, long/short plantar), muscular (tib post is key).
- “Windlass: hallux/MTP dorsiflexion tightens the plantar fascia → raises arch + inverts hindfoot → rigid lever; Jack's test demonstrates it.
- “Subtalar pronation unlocks the transverse tarsal (Chopart) joint (flexible); supination locks it (rigid) - the foot is a shock absorber at heel strike and a rigid lever at push-off.
Functional Anatomy & the Arches
Regions and joints. The hindfoot (talus, calcaneus) meets the midfoot (navicular, cuboid, three cuneiforms) at the transverse tarsal (Chopart) joint. The midfoot meets the forefoot (metatarsals, phalanges) at the tarsometatarsal (Lisfranc) joint.
The arches. The bones form three arches:
- Medial longitudinal - calcaneus, talus, navicular, cuneiforms and the medial three metatarsals; higher and more mobile
- Lateral longitudinal - calcaneus, cuboid and the lateral two metatarsals; lower, flatter, and in contact with the ground
- Transverse - across the cuneiforms and metatarsal bases
Three layers of support. The arch is held up by bone, ligament and muscle. The ligaments are the main passive supports, and tibialis posterior is the key dynamic one.
- Bony (static) - the wedge-shaped tarsals and metatarsals, with the talar head and navicular as the keystone of the medial arch
- Ligamentous - the plantar fascia (aponeurosis), the spring (plantar calcaneonavicular) ligament supporting the talar head, and the long and short plantar ligaments
- Muscular (dynamic) - the intrinsic foot muscles and especially tibialis posterior, whose failure causes adult acquired flatfoot, with peroneus longus and the long toe flexors
The Windlass Mechanism & Arch-Spring
The cable. The plantar fascia runs from the medial calcaneal tubercle to the bases of the proximal phalanges, passing beneath the metatarsal heads. When the metatarsophalangeal joints dorsiflex as the heel rises and the toes extend at push-off, the hallux most of all, the fascia winds around the metatarsal heads like a cable around a drum: a windlass.
What the windlass does. Winding shortens the distance between the calcaneus and the metatarsal heads, elevates the medial longitudinal arch and inverts the hindfoot. Together these stiffen the foot into a rigid propulsive lever.
Jack's test. Passively dorsiflexing the hallux and watching the arch rise is Jack's (Hubscher) test. It is used to assess a flexible flatfoot and the integrity of the windlass.
The arch-spring. The arch is also an elastic spring. The plantar fascia and the other arch tissues stretch and store strain energy as the arch flattens under load in early-to-mid stance, then recoil and return that energy at push-off, improving the efficiency of walking and running.
Spring and windlass together. High-speed imaging shows the plantar fascia is not perfectly isometric: it strains through stance. It still behaves as a near-ideal windlass during propulsion, with its shortening timed to enhance arch recoil at push-off.
The Gait Cycle & Joint Coupling
The cycle. A gait cycle runs from one heel strike to the next on the same foot and is about 60% stance and 40% swing. Swing has initial, mid and terminal phases. Stance proceeds through five:
- Initial contact (heel strike)
- Loading response
- Midstance
- Terminal stance (heel off)
- Pre-swing (toe off)
The three rockers. The body advances over three rockers:
- Heel (1st) rocker at heel strike - the ankle dorsiflexors control plantarflexion
- Ankle (2nd) rocker in midstance - the tibia rolls forward over the fixed foot
- Forefoot/MTP (3rd) rocker at push-off - the body pivots over the metatarsal heads, engaging the windlass
Flexible, then rigid. The foot must be flexible to absorb load at heel strike and rigid to push off. The subtalar joint controls the switch through the transverse tarsal (Chopart) joint, whose talonavicular and calcaneocuboid axes either line up or diverge.
At heel strike. The subtalar joint pronates (everts) and the two axes become parallel. The midfoot is unlocked, and the foot is a flexible, mobile shock absorber that adapts to the terrain.
In terminal stance. The subtalar joint supinates (inverts) and the axes become non-parallel. The midfoot locks and, together with the windlass, the foot becomes a rigid lever for efficient propulsion.
When the coupling fails. Loss of this coupling underlies many deformities. A foot stuck in pronation, as in tibialis posterior dysfunction, cannot lock and re-supinate, giving an inefficient flatfoot gait.
Clinical Relevance
Where the mechanics fail. Each of these conditions is covered in its own topic (Plantar Fasciitis, Adult Acquired Flatfoot / PTTD, Pes Cavus and Hallux Rigidus).
- Plantar fasciitis - overload of the highly stressed plantar fascia at the medial calcaneal tubercle, where its energy-storage role leaves it highly loaded; modelling shows peak fascia tension late in stance, increased substantially by the windlass
- Pes planus (flatfoot) - failure of the arch supports, dynamic (tibialis posterior dysfunction) and/or static (spring-ligament failure); the hindfoot stays pronated and the arch collapses. Jack's test and the double/single heel-rise test assess flexibility and tibialis posterior
- Pes cavus - a high, rigid arch, often neuromuscular, that overloads the heel and metatarsal heads
- Hallux rigidus and first-ray problems - loss of MTP dorsiflexion impairs the windlass and the forefoot rocker
Surgery. Arch-restoring procedures (for example medialising calcaneal osteotomy, tendon transfers and lateral-column lengthening) and fusions are designed around restoring this bony-ligamentous-muscular balance and the flexible-to-rigid mechanics.
The Subtalar Joint Axis & Triplanar Motion
The flexible-to-rigid switch turns on subtalar "pronation" and "supination", so the axis and what those words mean are core viva basic science. Subtalar pathology and fusion are covered in the Subtalar Arthritis and Subtalar Arthrodesis topics.
The oblique axis. The subtalar joint moves about a single oblique axis running from postero-lateral-plantar to antero-medial-dorsal. It is classically inclined around 42 degrees from the horizontal (transverse) plane and deviated roughly 16 degrees medial to the long axis of the foot, with wide individual variation. Because the axis is oblique to all three body planes, motion about it is triplanar.
What the words mean. Each term names three movements of the calcaneus/foot at once: pronation = eversion + abduction + dorsiflexion, and supination = inversion + adduction + plantarflexion. The heel-strike "pronation" therefore everts, abducts and dorsiflexes simultaneously, and push-off reverses all three, which is why describing only "eversion" is incomplete.
The torque converter. The talus, gripped in the ankle mortise, links leg rotation to foot posture like a mitred hinge: internal rotation of the tibia drives subtalar pronation, and external rotation drives supination. The subtalar joint is the torque converter between the transverse-plane rotation of the limb and the frontal and sagittal motion of the foot. With the transverse-tarsal coupling, this is the mechanism that unlocks the foot at heel strike and locks it for push-off.
"Pronation unlocks, supination locks" is shorthand for a triplanar motion about an oblique axis driven by tibial rotation.
The First Ray, Peroneus Longus & the Foot Tripod
Peroneus longus locks the first ray. Peroneus longus runs under the cuboid to insert on the base of the first metatarsal and medial cuneiform, and plantarflexes and stabilises the first ray against the ground. This locks the medial column, so that when the hallux dorsiflexes at push-off the windlass has a stable anchor to tension the plantar fascia. Its antagonist for first-ray position is tibialis anterior.
The tripod. Body weight is shared across a tripod of the calcaneal tuberosity and the first and fifth metatarsal heads, with the transverse arch spanning the metatarsal heads. Even load-sharing across this tripod depends on a first ray that can bear its share.
First-ray insufficiency. A dorsiflexed or hypermobile first ray (for example with tibialis posterior dysfunction, hallux valgus or a hypermobile medial column) fails to plantarflex onto the ground. Load transfers laterally to the second and third metatarsal heads, causing transfer metatarsalgia, and the windlass is weakened. Conversely, a plantarflexed, rigid first ray drives a forefoot-driven cavus.
Why it matters surgically. Restoring first-ray stability and plantigrade position (Lapidus/first-TMT procedures, peroneus longus function, medial-column realignment) is part of correcting flatfoot and forefoot overload. Hallux and forefoot pathology are developed in the Hallux Rigidus, Adult Acquired Flatfoot and Pes Cavus topics.
Mnemonics & Memory Aids
BLM (arch support)
Hook:Arch support = Bony, Ligamentous, Muscular (B-L-M).
PURL
Hook:PURL: Pronation Unlocks, Re-supination Locks.
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“Describe the arches of the foot and how they are supported, and explain the windlass mechanism.”
“How does the foot change from a flexible structure at heel strike to a rigid lever at push-off during gait?”
Anatomy
- Hindfoot (talus, calcaneus) | Midfoot (navicular, cuboid, 3 cuneiforms) | Forefoot (MTs, phalanges)
- Chopart (transverse tarsal) and Lisfranc (TMT) joints
- Medial (higher, keystone talar head/navicular) + lateral longitudinal + transverse arches
Arch support (3 layers)
- Bony/static: bone shape; keystone = talar head/navicular
- Ligamentous: plantar fascia, SPRING (calcaneonavicular) ligament, long/short plantar
- Muscular/dynamic: intrinsics, tibialis posterior (key), peroneus longus, toe flexors
Windlass & arch-spring
- MTP/hallux dorsiflexion winds plantar fascia round met heads → raises arch + inverts hindfoot → rigid lever
- Jack's (Hubscher) test demonstrates it
- Arch-spring stores/returns energy; peak fascia stress at medial calcaneal tubercle
Gait & coupling
- ~60% stance / ~40% swing; heel, ankle, forefoot rockers
- Heel strike: subtalar pronation → Chopart axes parallel → flexible (shock absorber)
- Push-off: subtalar supination → axes non-parallel → midfoot locked + windlass → rigid lever
Evidence & Key Studies
The extensibility of the plantar fascia influences the windlass mechanism during human running
- Using high-speed X-ray during running, the plantar fascia was shown to both store/release elastic energy (arch-spring) AND act as a windlass coupling toe dorsiflexion to arch shape.
- Toe plantarflexion at foot strike delays plantar-fascia stretch, redistributing load through other arch tissues.
- In propulsion a quasi-isometric (near-ideal windlass) fascia shortens later in stance, enhancing arch recoil at push-off - reconciling the arch-spring and windlass models.
Finite element analysis of plantar fascia during walking: a quasi-static simulation
- In a 3-D finite-element model, plantar-fascia tension peaked at pre-swing (about 83% of stance) at roughly 493 N (about 0.7 body weight).
- Stress concentrated near the MEDIAL CALCANEAL TUBERCLE - the typical site of plantar fasciitis - and the windlass mechanism increased fascia tension by about 66%.
- Reducing heel rise and Achilles tendon force lowers fascia loading, supporting calf-stretching and gait modification in plantar fasciitis.
The combined arch-spring/windlass behaviour of the plantar fascia comes from the cited Welte study, and the peak fascia tension, the medial-calcaneal-tubercle stress concentration and the ~66% windlass contribution from the cited Chen finite-element analysis. The arch anatomy, the three layers of arch support and the subtalar/transverse-tarsal coupling are standard, well-established functional anatomy. (See also our Plantar Fasciitis and Adult Acquired Flatfoot topics.)