Any runners around the campfire?

After playing soccer for 30 years and running quite a bit, I find that it's just too painful anymore. The joints in the legs and spinal compression are exacerbated by running when you get older. I turned to cycling about a decade ago. Low impact but fantastic exercise and I've worked myself up to 24 hour mountain bike races, multi day rides, and century road rides. My resting heart rate and BP are really low and lung capacity is awesome. And the sites I've seen. I applaud your effort to get in shape, but be careful with your joints. Running is hard on your body. As far as going into the red zone with heart rate, the risk is a heart attack, passing out, o2 deprivation or any myriad of issues. You are working beyond capacity of what you should be and taxing organs more than is healthy. Stay in your target HR and work up to expanding those limits. What's the point of pushing too hard? A gradual increase has more long term benefits than going too hard.