Although I've been doing a fair amount of stretching in the morning, for the past 10 years, I started being more aggressive about it a few weeks ago, working on keeping my knees flat on the floor while seated and bending forward so my chest is on the floor. Great sense of accomplishment doing so :-) However, I've noticed my legs cramping up during my afternoon runs (3 miles). I'm wondering if I'm doing some serious damage to the tendons in my legs by over stretching and then running. Is there such a thing as being too loose in the joints.? Are overly flexible hip and knee joints and running mutually exclusive? Should I back off on the stretching and be content with stiffer knee joints but being able to run without cramping up? Or will the cramping gradually go away as my legs adjust?
I'm 66, and unfortunately have lost the flexibility of youth :-(

Thanks