The coach's statement is not completely unreasonable. You are still young (in the development stage), and your inexperience can easily cause internal injuries. Your common sense in all aspects may not be very good, such as inhaling when you should exert yourself, and inhaling when you don't exert yourself (unreasonable exertion will seriously hurt your internal organs); And the personal trainer has enough ability to help you solve it!

Of course, hiring a personal trainer is not affordable for young people aged 17 (except rich children)!

So do what you can and don't try to be perfect! ! !