I think all forms of exercise provide a health benefit. My boyfriend just went from 300 pounds to 195 pounds from February to now. However, he didn't just do it with just cardio activities. He mixed cardio with strength training with flexibility. All three are absolutely necessary.
If you do cardio without nurturing your joints you could destroy your knees, which means no more running. If you do cardio without strength training you run into other support-system issues.
Also if you do the same thing over and over again your body builds resistance to that activity - it no longer puts out the same effort doing it.
So the most effective systems mix it up every day. Each day you do something new, focusing on a different part of the body. If all you did was cycle every day, then your legs would become quite efficient at that one motion. It would no longer truly strain your legs. The rest of you would not get a great workout.
You would want to cycle one day, box the next, do yoga the third, and so on. It's about using all of the muscles, in different ways, stretching all the body parts, in different ways, and twisting in all directions as well.
It's great that you like cardio! It sounds like it's a good time to start looking into strength training and flexibility activities to round out your body's experiences.
Lisa Shea, Owner