im 19 and have quite a good level of fitness. But nowhere near what i need or want to get to Top Level Badminton. This is because i get to the peak of my current training program than have had an injury so instead of starting my new harder training program and improving fitness lots, it stays the same or drops. And yes its while doing intense cardio workouts like pulse bike training and stuff. My heart rate gets to around 150 and doesnt seem to get too much higher. Maybe for sprints and stuff i think 160 or a bit higher. But not too high as my level of fitness is still good compared to average teenagers.