Prisoner squat

Stand with your feet a little wider than shoulder width apart with your toes slightly turned out and your hands behind your head.  Pull your elbows backwards, lift your chest and pull your shoulders down away from your ears.

Then, sit into the squat, imagining there is a chair just behind you (in fact you can use a chair to create the right association). Bend your knees and push your bum backwards, arching your lower back as you go. At the same time, keep opening your elbows to the sides and lifting your chest, whilst pulling your shoulder blades together and down at the back. Keep your knees in line with your second toes throughout.

Go as low as you are able to maintain an inwards curve in your lower back and pause briefly at the bottom position before pushing up through the legs to stand.  Try to keep your torso as upright as possible through the movement.