What is actually going on under your heel
You do not need to memorise every structure. You do need to know three things: where the fascia attaches, why the calves drive most of the load, and how the windlass mechanism works. Those three facts explain every stretch on this site.
First, the name
“Plantar fasciitis” literally means inflammation of the plantar fascia. It is almost always misnamed. When researchers biopsy the painful tissue in chronic cases, they find degenerative changes, not the cellular markers of acute inflammation. Lemont and colleagues coined the term “fasciosis” in 2003, and clinicians increasingly use “plantar fasciopathy” instead.
Why does this matter to you? Because it changes the treatment. Anti-inflammatories alone do not fix a degenerative tissue. What does, over weeks and months, is mechanical load management: stretching the structures that pull on the fascia, mobilising the fascia tissue itself, and once you are past the reactive phase, loading the tissue eccentrically to remodel it.
The plantar fascia: a band, not a muscle
The plantar fascia is a thick fibrous band of connective tissue on the underside of your foot. It is not a muscle: it does not contract, it does not relax on demand. It is more like a thick, slightly elastic ligament.
- · Origin: medial calcaneal tuberosity. This is the inner-front edge of your heel bone. It is almost always where the pain is.
- · Insertion: the base of each of the five toes (proximal phalanges).
- · Function: supports the medial longitudinal arch and helps transmit force during the push-off phase of walking and running.
Because the fascia is fibrous and slow-healing, it does not recover quickly after irritation: timelines are weeks and months, not days.
The windlass mechanism (why big-toe extension matters)
Here is the most useful piece of mechanics for understanding plantar fasciitis. When you extend your big toe (pull it up toward your shin), the fascia wraps around the head of the first metatarsal bone and is pulled taut. This raises the arch and tensions the whole fascia.
This is called the windlass mechanism, after the boat winch. Two practical consequences:
- · It is a self-test. If extending the big toe reproduces or sharpens your heel pain, that is a positive windlass test, strong evidence the fascia is the source.
- · It is a stretch technique. The big toe extension stretch on this site uses the windlass to load the fascia directly, which is more effective than calf stretches alone in DiGiovanni et al.'s 2003 trial.
The calf load chain (why the muscles above your heel matter)
The calf, the Achilles tendon, and the plantar fascia form one continuous mechanical chain. When you walk, force travels from your calf, through the Achilles, around the back of the heel, and into the plantar fascia.
Gastrocnemius (the bigger, more visible calf muscle)
Crosses both the knee and the ankle. Stretched with a straight back knee in the wall stretch. Tightness here limits ankle dorsiflexion, which means more load is transferred onto the plantar fascia during push-off.
Soleus (the deeper calf muscle)
Crosses only the ankle, not the knee. This is the one most people miss when they stretch their calves. Stretched with a bent back knee, which takes the gastrocnemius out of the equation and isolates the soleus.
Achilles tendon
Connects the calf muscles to the heel bone. It is continuous with the plantar fascia via the periosteum of the calcaneus: load travels from one straight into the other. This is why eccentric calf loading (the Alfredson protocol for Achilles tendinopathy) was adapted by Rathleff and colleagues into the eccentric heel-drop protocol for plantar fasciopathy.
Intrinsic foot muscles
The small muscles inside the foot itself. McKeon and colleagues (2015) framed these as the “foot core”: when they fail to share load with the fascia, the fascia takes more force. The towel scrunch on this site is the entry exercise to wake these back up.
Why your heel hurts most in the morning
Two reasons. First, during sleep, your foot relaxes into plantarflexion (toes pointed), which lets the fascia shorten over the night. Second, while you sleep, any healing or tissue remodelling that has been happening is in its quietest, least-blood-flow state.
When you stand up in the morning, that shortened, stiff fascia gets suddenly loaded under your full bodyweight. The first few steps stretch it abruptly, which feels like a sharp tear.
The fix follows directly from the mechanism: lengthen the fascia BEFORE you put weight on the foot. The morning-in-bed routine on this site is built for exactly this.