There is a wide range of what it means to be a "high achiever academically." For some people, this means all As. For some people it means all As in all honors classes. For some people it means all As in the most difficult classes available for your grade level, whether that be accelerated or advanced classes beyond honors. For some people that means getting all As in AP classes as a freshman, even though those classes are mainly the talented juniors/seniors. And so on and so forth.
At academically demanding high schools, 1 hour or more of homework/studying per class per night is not unusual, and it is not busy work either. Some kids fill their schedule with classes and electives and have no study halls.
I would imagine it is very difficult to be a high level gymnast and practice 4+ hours a day, plus travel time to and from the gym, and study for 5+ hours a day, in addition to the school day, plus get a decent amount of sleep.
My dd is 8 and has minimal homework, but needs to sleep a lot. She goes straight from school to gym, and does homework in the car. She eats dinner on the way home in the car. She gets home, empties her school bag, repacks her school bag, talks to me for 15 minutes, takes a shower, and goes to bed. I have no idea how she will continue with even more hours in the gym and more homework. I really hope she needs less sleep in the next couple of years, or I don't know how she'll get through elementary school, much less middle or high school.