Well done on your running. Now you've sorted your cardio, you could think about resistance work - you need to build up the muscles that will support your running (the side effect of working on these muscles will be to give you a bigger bum (shapely bigger)).
As Shed said, do squats, do them with weights if you can. Do some lunges with weights and maybe some deadlifts - these will all build up your glutes and hip and thigh muscles. Have a look at the resistance machines for legs when you're in the gym and see if you can have a go on them
Be careful when you get started, either get someone to show you to squat properly or watch some good videos online. Doing them wrong can hurt your knees, but doing them right will help running and bum shape. (Also, muscle will burn calories just by being there, like a BOGOF.)
Cycling will build muscle indurance, so it's a really useful exercise, but it won't actually put muscle on (it might put some on your calves, but will only really build your thighs if you're working them to fatigue at a heavier weight than you're used to - it's not likely you're going to be doing this).
Use your cycling as a good cardio workout and get some resistance work done to build the muscles up.
It's pretty cool, isn't it I remember when I started and the weight fell off me. That was seven years ago and it's never really gone back on.
Get your form perfect before you add weights in. It's best to start off doing them in front of a mirror so you can keep an eye on your alignment. If you can do them perfectly, then add some weights in your hands and your bum will start to build back up again. Good luck.
Cycling up hills will give you a muscly bum (and big quads)....you’ll never seen a cyclist with a flat arse!! If you’re using an indoor trainer you can replicate hills by peddling (staying seated) at ahigh resistance with low cadence (about 40-50RPM) so you’re really grinding to keep the peddles turning. Do it as intervals though rather than a solid block, that’d be dull. You may find a gym type exercise bike has a hill programme you could use.
It’s shit isn’t it. I find when I run or exercise a lot I just end up straight up and down. Over the last year I have put on a few pounds and my boobs and bum are so much better.... but I have a muffin top and am less fit. Would love to find the answer!
Spent 6hrs clearing the garden while it was sunny and all those glute muscles ache from bagging up the rubbish so that's good.
I find my chest is fine doesn't seem to be shrinking but there is a noticeable change in the butt from the running. I've told DH this might be my new shape and he will have to accept it and he's sad as he prefers curves but supporting the exercise as it's done me a lot of good.