A helpful exercise for/to your abdomen

Question

I know that we can say something is helpful to/for someone like in

“This information would be extremely helpful for/to teenagers.”

I wonder if it is okay to say something is helpful to/for something

For example, let’s say I am teaching someone a particular exercise; can I say either of these sentences to him to mean that that exercise is effective for his stomach:

This is a helpful exercise for your abdomen.

This is a helpful exercise to your abdomen.

Or let’s say I think a book is effective at improving kids’ imagination, can I say either of these:

“This book is helpful for kids’ imagination.”

“This book is helpful to kids’ imagination.”

I am asking this question because I can’t find the structure “helpful to something” in dictionaries and that structure sounds a little bit off to me - especially when I put “to” instead of “for” after “helpful.”

Answer 1

The object of "helpful to" is the person who will find it helpful. From that person's perspective, it is helpful.

The object of "helpful for" is either the same as above, or the object or task that will receive a benefit.

So, we can say either it's helpful "to" or "for" students, but for your other two examples, where the object is not a person with a perspective, you can only use "for":

This is a helpful exercise for your abdomen.

This book is helpful for kids’ imagination.

Answer 2

using to or for in a sentence will be depending on the type of action conveyed by the sentence If you're recommending your book or exercise or it's preferably you use for