How much exercise is over exercise. i regulary cycle for 50 kms in a stationary bike .

Exercise: How much you exercise depends on your goal. If what you want is good conditioning then 30-60minutes a day of aerobic mixed in with 3 days a week of strength training is good. If you're training for distance biking, running or some other goal, then a training program specific to the goal is needed. If you're exercise beyond what you need for your goal, you could be said to be 'overexercising'.