Here is a cool modified squat that hits all those trouble spots. Butt, arms, thighs, core. Boom.
Step 1: Stand with feet a little more than shoulder width apart and point your toes out slightly. Hold a dumbbell (5-12 lbs. depending on your fitness level) in front at waist level.
Step 2: Keeping your arms straight, lift the weight to shoulder height as you lower slowly into a squat. Hold for 2 counts and then slowly return to the starting position.
***Always maintain control of your movements. NO swinging!***