Oh. My. God.
This is the best £25 I have ever spent. EVER.
I think I have tendonitis in my Achilles tendon (that's my diagnosis anyway from my internet research). I get a vast amount of pain at the beginning of a hill walk that takes almost precisely 1.5 miles to disappear. And, yes, I have recorded it. After that nothing, but boy, does it drain my energy. My brother bought some of these as he has a tendency (no pun intended) to cramp and raved about them, so I ordered a pair just before a two week walking holiday in the Lakes. They are revolutionary. They are pretty tight but you don't really notice you're wearing them but do make sure you measure your calf to get the right size. They hold your muscles tightly to avoid excess movement and deliver more blood to your muscles. They are amazing. I still had the pain, but it was bearable and it wore off much more quickly. It makes your legs feel strong and supported and less tired and after a long 11 mile walk with four mountain tops, my legs still felt fresh. We both also had no stiffness or aches the following mornings. In fact, when we walked without them, we felt most peculiar - weak and feeble!
How much is a placebo and how much is actual science I don't know and frankly don't care. They certainly helped me and my brother and we now wear them for cycling too. A fantastic product. Thinking about the full length tights now too....