I have a friend, Bruce, in Las Vegas, and one of the visitors to his blog used the word "brittle" to describe how our bodies age. I like that word. Something that is brittle cracks under stress rather than bending.
"Brittle" describes my body. Up until I was 71, I didn't notice a lot of difference in my body then as compared to my body when I was younger. But, in the subsequent two years, I've discovered that my body is aging and is becoming more "brittle". I'm having to make increases in distance and speed at a slower rate than I did two years ago. I'm having to allow more time for recovery after a stressful run than I did two years ago. Yes, my body is becoming "brittle".