Front knee doesn't travel over the toes
Ankle stiffness prevents the forward knee drive needed for the stretch.
Overactive muscles
SoleusGastrocnemius
Corrective work
Foam RollCalves↗StretchWall calf stretch — soleus (knee bent)↗Ankle stiffness prevents the forward knee drive needed for the stretch.
Lower back arches instead of the hip flexor lengthening.