SLSq with rotation floor reach ("Hip hinge, single leg squat" Posterior chain strengthening, with rotation)

Stand up straight and take your weight onto one leg.
Lift your elevated leg back behind you and across.
Simultaneously reach your arm on the same side down towards the floor and across the front of your stance leg to reach the floor on the other side.
Ensure you keep your back straight throughout this movement, avoiding any rounding or arching in the back.
As your stance leg bends your knee should travel directly forwards over your toes.