Static Diagonal Heel Lift: isometric knee to hand push + 2nd. heel lift
With the PBU at 30-35 mm Hg or other hand to monitor that no pressure change, slowly lift one knee towards the opposite hand and push them isometrically against each other on a diagonal line. While keeping this pressure slowly lift the second heel off the floor and bring it up beside the first leg. Hold this position for 10 seconds and repeat 10 times so long as control is maintained (no pressure change).
As soon as any pressure increase or decrease is registered the movement must stop and return to the start position. The point of greatest risk of losing stability is when the second heel leaves the floor. Do not allow substitution or fatigue.