I was chatting to a friend of mine who is a podiatrist and I told her how bruised I was feeling under my heels when I walk and run. She explained that as we get older, the amount of fat under our heels reduces (I'm 55). We literally have less cushioning there. She was going to send me some specially shaped insoles to try out. However, sometimes, in summer, I wear flat converse style shoes with good quality cushioned insoles and I popped them into my trainers. What a massive difference. I felt like I was running on air!
I had thought it was tight calf muscles. I'm so happy to know there was an easy adjustment to try and thought I'd share in case anyone else suffers from the same.