Nested form 3 levels deep

Hello All,

I'm trying to build a workout app that stores your routine. I believe I need to build nested form that three level deep. The relationship is as follows:

1. workout_cycle has_many:
2. workout_days has_many:
3. exercises has_many:
- sets
- repetitions

I've heard that one shouldn't go more than two levels deep. If that's so how should build my association?