In a society of sitters it shouldn’t be a surprise that our butts are starting to atrophy.  What is atrophy?  According to Webster’s Dictionary it is “the wasting away of a body part or tissue” and in this case we are talking about our butt muscles. 
Our butts can’t help it.  We spend so much time at desks and in cars, which means our glutes are stretched for upwards of eight hours a day or more.  Remember, the muscles of the glutes are what help us stand upright.  So our glutes work to straighten the body and are at ease when we bend forward or sit down.
But there are quick and easy things you can do to help.  Engage your butt whenever you think of it.  Engage it in the office; engage it in the car.  Try flexing one side of your butt and then the other. 
Walk more.
Do squats.
Stand up during intervals throughout the day.
Eat lunch standing up.
Get off the couch (especially if you sit at work all day)
Try this glute series that one of my clients named the “Butt Blaster”
You’ll need a stability ball.
Lay over the ball with you bottom rib and stomach completely supported on the ball.  Have your upper body propped up on your forearms.  If at any point your low back hurts, take a break or stop.  Your back should NOT hurt at all.  If your back hurts, you are doing the movement from your back, not your butt.  To help try and keep it out of the back, keep gently engaging your abs by pulling your navel to your spine.
Lift and lower both legs together.  (Don’t’ lift higher than straight in line with your body.)
Hold the legs straight in line with your body and do small, scissor kicks.
Hold the legs straight in line with your body and do small circles in each direction.
Laterally rotate the legs and gently tap your heels together inhaling for a five count, exhaling for a five count.
Do all of these sets for a count of ten.  You may need to build up to ten.