Parabolic Curve
Using the banister, lean over backwards, reach out and place palms of hands on wall. Then "climb" down the wall as far as possible, whilst stretching out one or two legs to counterbalance the weight and produce a parabolic curved body shape.
1
Locate a banister ideally a metre away from a facing wall, parallel to the banister.

2
Sit upon banister, place one foot on opposing wall.

3
Lock other foot behind banister spindle and grasp banister rail with both hands leaning back slightly.

4
Lean back further and place hand onto the wall behind.

5
Place other hand upon wall behind.

6
Using hands, climb down the wall as far as possible, arching back, and thus creating a parabolic curve.

Notes
Ensure that your back and neck are stretched beforehand to avoid injury.