Achilles Tendinopathy vs. Plantar Fasciitis: How to Tell the Difference

Both conditions cause heel-region pain, both are common in runners and people who stand for work, and both are often treated with the same advice regardless of which one you actually have. But the plantar fascia and the Achilles tendon sit on opposite sides of the heel bone, answer to different loading patterns, and respond to different exercises. Getting the diagnosis right is the difference between weeks and months of recovery.

In this piece I'll walk through how to tell them apart from what you feel, a five-question differential you can run at home, what the overlap looks like when both are irritated at once, and how treatment should diverge once you know which tissue you're dealing with.

Why they get confused

Three reasons:

1. Location sounds similar. Both hurt "around the heel." Unless you've done the mental mapping of fascia-underneath vs. tendon-behind, the brain files them together.
2. First-step pain overlaps. Both conditions are famously worse in the morning or after sitting. That symptom alone doesn't distinguish.
3. They coexist. In maybe 15–25% of cases, the same person has moderate plantar fasciitis and moderate Achilles tendinopathy at the same time — usually driven by tight calves and training overload.

Here's the cleanest split.

The anatomy, in one page

The plantar fascia runs along the bottom of the foot, from the underside of the heel bone to the base of the toes. It stretches when the arch flattens and recoils to push you off. Its pain lives under the heel.

The Achilles tendon runs along the back of the ankle, connecting the calf muscles to the back of the heel bone. It lengthens when the ankle dorsiflexes and contracts to plantarflex the foot. Its pain lives behind the heel or a few centimetres up into the calf.

Both tissues share a continuous fibrous envelope at the back of the heel bone (the paratenon-to-fascia continuity), which is part of why tightness in one loads the other. A broader anatomy primer is in understanding the different types of heel and foot pain.

The differential — 5 quick questions

Answer these. Most of the time the pattern is obvious:

1. Where exactly does it hurt? Point with one finger. If it's on the underside of the heel (or the inside-front edge of the heel bone), fascia. If it's on the back of the heel or 2–6 cm up into the lower calf, tendon.
2. What movement makes it worst? Pushing off the ball of the foot or walking uphill → more likely fascia. Rising onto the toes or a single-leg heel raise → more likely Achilles.
3. Is the tissue visibly thickened? Thumb along the back of the heel up into the calf — a distinctly thick or ropy spot, sometimes tender, is a classic Achilles sign. The plantar fascia can thicken too, but you can't palpate it as easily.
4. Does it hurt to pull the big toe up? Dorsiflexing the big toe pre-tensions the plantar fascia (the "windlass"). If that reproduces sharp pain under the heel, fascia. Rarely reproduces Achilles pain.
5. Did it start after hill sprints or uphill running? Heavy eccentric loading of the calf strongly biases Achilles. A new job standing all day or long flat walking biases fascia.

Treatment — overlap and divergence

Both conditions share a core treatment backbone because both are load-sensitive tissues that respond well to progressive loading [1, 2]:

• Both benefit from heavy-slow calf raises. The protocol differs slightly — knee bent vs. straight mix, and with toes dorsiflexed for the fascia.
• Both respond to relative rest, footwear changes, and gradual return to activity.
• Neither tends to respond well to total immobilisation. They are load-craving tissues; too much rest often makes them worse.

Where they diverge:

• Plantar fasciitis: benefits more from plantar-fascia-specific stretching (the DiGiovanni protocol), night splints, and arch support. Heel lifts can help temporarily.
• Achilles tendinopathy: benefits far more from heavy-slow resistance training on a step (heel dropping below level), the Alfredson protocol, and the patience not to compress with arch taping or aggressive stretching early.

Over-stretching an irritated Achilles with the foot dorsiflexed can worsen symptoms — this is important if you're used to PF-style calf stretching. For Achilles specifically, neutral-foot eccentrics are the evidence-backed path [2]. We go deep on the PF side in a complete home exercise program for plantar fasciitis.

What if you have both?

Co-existing plantar fasciitis and Achilles tendinopathy is common in runners and in people with very tight calves. In that case:

1. Treat the more painful one first with its specific exercises (usually 2–4 weeks of targeted loading).
2. Don't do both stretching programmes aggressively at once. Calf stretching for PF can aggravate an irritated Achilles.
3. Address calf tightness systemically. Soft-tissue work on the calf, mobility work on the ankle, and footwear with a small heel-to-toe drop all reduce load on both tissues.
4. Get imaging if neither improves in 8 weeks. Ultrasound can confirm both diagnoses and rule out partial tears, which changes the plan.

Finally: if you're uncertain, see a professional. A brief clinical exam resolves this in about ten minutes. The escalation guide is at when to see a podiatrist. Guessing wrong costs weeks. Getting it right costs a consultation.