Start standing in front of a box or bench with dumbbells in hands at sides and left foot resting flat on top of the bench. (mindbodygreen.com)
Perform a squat as described above but with dumbbells held in the rack position — at shoulder level with elbows pointing forward. (onnit.com)
The use of dumbbells instead of a barbell forces you to stabilize your core and shoulders all through the movement, thereby strengthening the smaller muscles that otherwise don't get enough work. (fitnessandpower.com)