Achilles tendonitis typically starts as a mild ache in the back of your leg or just above your heel, most noticeable after physical activity. The pain can range from a dull stiffness to a burning sensation depending on how far along the condition has progressed and what you’re doing when you feel it. Here’s what to expect at each stage and how to tell it apart from something more serious.
Where Exactly You’ll Feel It
The Achilles tendon runs from your calf muscles down to your heel bone, and tendonitis can strike in two distinct spots along that path. Non-insertional tendonitis causes pain roughly 2 to 6 centimeters above where the tendon attaches to your heel. You’ll feel it in the thick middle portion of the tendon itself. Insertional tendonitis, by contrast, hurts right at the back of your heel where the tendon connects to bone. That version often comes with swelling or tenderness directly on the heel, and it can make wearing certain shoes uncomfortable because of pressure on that spot.
Both types produce pain along the back of the lower leg, but knowing which location matches your symptoms helps you understand what’s going on. Insertional tendonitis is more common in people who aren’t necessarily athletes, while non-insertional tendonitis tends to show up in runners and people who are active.
The Morning Stiffness Pattern
One of the most recognizable signs of Achilles tendonitis is how it greets you first thing in the morning. Your first steps out of bed feel stiff and achy at the back of your ankle. The tendon tightens overnight while you sleep, so those initial movements can feel like you’re walking on a leg that hasn’t loosened up yet. This stiffness generally improves as you move around and the tendon warms up throughout the day.
This morning pattern is actually one of the features that distinguishes tendonitis from a more acute injury. If you notice your pain is worst in the morning and eases with gentle movement, that’s a classic tendonitis signature.
How It Feels During and After Exercise
The relationship between Achilles tendonitis and activity follows a predictable cycle. At the start of a run or workout, you’ll feel stiffness or mild discomfort. Many runners describe pushing through this initial phase because the tendon seems to warm up and the pain temporarily fades. That “warming up” window can trick you into thinking the problem isn’t serious.
But after longer or more intense activity, the pain returns and escalates. Stair climbing and sprinting tend to produce more severe burning or aching because they load the tendon heavily during push-off. The day after a hard session, you may feel noticeably more sore than you did during the activity itself. This pattern of “hurts, then loosens, then hurts worse” is what catches many people off guard. Rest relieves the symptoms, which makes it tempting to keep training, but repeated loading without adequate recovery is exactly what drives the condition forward.
Physical Changes You Can See and Touch
Beyond pain, Achilles tendonitis produces visible and tactile changes. Swelling or tenderness at the back of the heel or along the tendon is common. In some cases, the tendon itself thickens over time. You might notice that the affected side looks or feels slightly bulkier than the other when you run your fingers along the back of your ankle.
In a specific form of the condition called paratenonitis, where the tissue surrounding the tendon becomes inflamed, you may actually hear or feel a squeaking, popping, or crackling sensation when you move your ankle. This crunching feeling happens because the inflamed outer layer of the tendon isn’t gliding smoothly anymore. It’s unsettling but not dangerous on its own.
How Symptoms Progress Over Time
Achilles tendonitis doesn’t stay static if you keep pushing through it. In its earliest stage, the condition involves inflammation of the tissue around the tendon. Pain at this point is typically limited to during or after activity and responds well to rest. Runners at this stage often describe discomfort at the beginning of a run that they can work through.
If the tendon continues to be overloaded without recovery time, the problem shifts from surface-level inflammation to actual changes within the tendon’s structure. At this point, the condition is more accurately called tendinosis, meaning the tendon itself has started to degenerate and weaken rather than simply being inflamed. Pain becomes more persistent and may bother you during everyday activities, not just exercise. Eventually, running at all becomes difficult.
The concern with advanced degeneration is that weakened areas of the tendon can progress to partial or complete tears, particularly during explosive movements like jumping, sprinting, or sudden direction changes. This is why the “push through it” approach carries real risk over time.
Tendonitis vs. a Rupture
One of the most important distinctions is between the gradual buildup of tendonitis and the sudden event of a tendon rupture. Tendonitis develops over days or weeks. A rupture happens in an instant.
People who rupture their Achilles tendon almost universally describe an audible pop or snap at the back of the ankle, along with the sensation of being kicked or punched in the back of the leg. As one orthopedic surgeon has noted, patients mention this “kick” sensation constantly. They turn around expecting someone to be standing behind them, and nobody is within ten yards. A rupture also causes immediate difficulty walking or pointing your foot downward, which is very different from the gradual stiffness and soreness of tendonitis.
If your symptoms have built gradually, involve morning stiffness that improves with movement, and get worse with activity, that pattern points toward tendonitis. A sudden, dramatic onset with a popping sound is a different situation entirely and needs immediate medical attention.
What Makes the Pain Worse
Certain activities load the Achilles tendon more heavily and tend to amplify tendonitis pain:
- Stair climbing: Forces your calf and tendon to lift your full body weight repeatedly through a range of motion that stretches the tendon.
- Sprinting or hill running: Increases the load on the tendon during push-off significantly compared to flat, steady-pace movement.
- Jumping and landing: Produces peak forces through the tendon, which is why basketball and football players are at higher risk for progression to tears.
- Prolonged standing after rest: Similar to the morning stiffness effect, any period of inactivity followed by loading can trigger discomfort.
The common thread is that the tendon hurts most when it’s asked to absorb or generate force after being at rest, and when the force is high or repetitive. Activities that keep the ankle in a neutral position with minimal calf engagement tend to be more tolerable.