I've been trying to lose weight for a few months and I recently started insanity which has been working great . But I was wondering if there's a way I can keep my backside the same or gain muscle there , if so how ?

I would do some squats and hamstring/glute exercises such as:

Lateral Lunges
Romanian Dead Lifts
Hamstring Curls
Normal Squats
Jumping jacks
Elliptical training
Forward lunges

Hi,
Thanks ,Jess
Very great information you share here.
Being active is an important part of any weight-loss or weight-maintenance program. When you're active, your body uses more energy. And when you burn more calories than you consume.

Glad I could help! And I totally agree! I would rather be healthy than skinny!