I cycle a lot (very hilly in hk) and have developed some pain in my left ankle. it burns when i stretch it. achilles' tendon or something else?

Achilles in back: If you have pain and point tenderness over the large tendon at the back of the ankle, then yes, think Achilles tendonitis. Burning, though, is sometimes a sign of nerve inflammation. The sural nerve can be irritated near the back of the ankle as well. Talking to a doc and/or providing more details could result in more answers. If I can help, then join my care team at healthtap.com/dr-clarkeholmes