My father was a track star in high school, and continued jogging almost every day. In his 30's, he was still a fantastic distance runner, placing well in running competitions. By age 42, his knees were done and he had to stop running completely.
A female friend from high school was also a track star. She, too, kept running afterward, staying very "fit" in her 30's, but suffering multiple health problems she considered "unrelated." To this day, she denies she has any health problems, but continues going to the doctor for all sorts of issues.
At age 38, I can tell story after story about "fitness" fanatics who felt they needed their hard exercise-- running, biking, weight-lifting, etc-- in order to stay healthy and look good. But the reality is hard exercise isn't that good for you after age 30. Sure, you can still do it in your 30's, but you're causing yourself problems. And in your 40's, the pain you feel from hard exercise is your body telling you "hard exercise is wrong for you."
Most generally, people exercise to look good. But if you've read my blog or listened to other health professionals, trimming body fat is a dietary function.
So if you want to be healthy, and exercise in a suitable, sustainable manner, you need to exercise gently. Chinese calisthenics like tai chi and QiGong gently work the entire body, including the cardiovascular system because they include super-special breathing practices. They also strengthen the trunk (build so-called "core strength") because they include postural practice. Your hard exercise has neither postural training or breathing training.
If you're over age 35, you need to take a good look around and see who USED TO exercise hard, but can't anymore. You need to look into the crystal ball and understand in earnest that hard exercise is not sustainable. In fact, it's not even what's keeping you looking good.
Keep exercising hard, and you will plague yourself with pain, health problems and deteriorating joints.
If you don't exercise at all, you need to start.
Exercise gently, and you will live longer and healthier. I beg you to listen to me, and act now.