HELP! how do i tell my sisters..?

You have the right to do what you're planning on doing without consulting your sister. If your sister doesn't like it too bad. You, not her has to live with the burden of sore back and neck muscles. It's really none of her business.

If you know how they will react, just do it. If your ballistic sister is prone to over dramatize and have hysterics over things that don't even involve her, this will probably be no different. You just have to deal with it. At least your mom and other sister will be supportive of your decision. The other one will just have to have her hissy fit, be the center of attention for a while, and move on. If she's so self-centered that she can't even let you do something to improve your health without making herself the object of attention, then she has problems. But you probably already knew that. Narcissists hate not being the center of the universe and this kind of thing will put you square in the center so she'll probably spend some time trying to think of something to bring the focus back to her. Do your thing and mind YOUR health and peace of mind.

If you can't muster the strength, that will be fine. Tell your more understanding sister in person. Either ask that sister to tell the other sister or tell her over the phone and then give her time to blow off steam if you think she's going to be upset.

how bout you go back to my question and read the things i added. so i can get a better answer from you?

and btw idnt think your sister should get mad at you its your choice and if your mom approves then it doesnt matter what your sis says because shes not ur gardian.

I think you should tell them anyways.They are your sisters they love you for who you are.

good luck!

i don't get....really??

if your mom knows it and happy for ur desicion then why u think ur sister will not....very confusing????? unless there's more detail here that u didn't include?????