Thanks you, Crimson, it is also very enjoyable!
I definitely feel the endorphin rush when I am walking and some of my more adventurous climbs bring on the adrenaline too! My motto is 'I will be very secure in the grave - now I want adventure'.
One of my grandsons became addicted to exercise and body building when he was about 18. He started to attend the gym nearly every night and put up a bar in his bedroom to do pull-ups. He was spending a lot of money on dietary supplements which seemed to be just whey powder. He does kick-boxing and also surf boarding (in the North Sea.....brrrrr!). Fortunately, he is now taking an NVQ in Public Services - I am not too clear about it but I think it is preparation for entry into the emergency services. It includes a lot of physical exercise - he is the least academic of all the children, so he is delighted to have found a course that is not solely classroom based. He is about 6' 3" and although he has developed his upper body muscles he remains about 12 stone.
I began my new walking regime today, as it was beautifully warm and sunny in this part of Switzerland. I found a path through a forest beside a river that tumbled over rocks in a series of waterfalls. The path was quite steep, but not the 'pulling myself up by tree roots' that I often tackle. I wanted to walk on and on, but I just did a circular trip of 90 minutes. This seems such a bizarre obsession, but it seems it is not that unusual.
I have not mentioned this to anyone else - you are a great bunch and I have listened to all your advice.
By the way, my arthritic knee has improved enormously since I started walking - I think I have strengthened the surrounding muscles and tendons.