Posture Movement Awareness Exercise: Quadruped Flexion and Extension

(you need a mirror and/or friend with a camera)
(a safe exercise for sore backs - but do take your time!)
Lumbar Flexion & Extension, Start:-

Kneel in the quadruped (or crawler position) - see diagram

Explore your Lumbar Flexion:- action

(Slowly!) exhale and round your back upwards - let your head hang and the back of your neck lengthen
Inhale back to the start
Repeat three times and on the third time, your friend takes a picture!

Explore your lumbar extension:- action

(Slowly!) inhale and hang your torso downwards - send your gaze to the wall in front and release & lengthen your neck away from your shoulders.
Inhale back to the start
Repeat three times
On the third time your friend takes a picture!

Lumbar Neutral in the Crawler Position:-

Come back to what you feel to be comfortable middle position for you
Your friend takes a picture

(Lumbar Flexion & Extension Scroll right>>>...)

Pictures: Lumbar Flexion & Extension in the Crawler Position

Start Position:-

Flexion:-
(Is this where you feel pain?)

Extension:-
(Or is this where you feel pain?)

Back to Neutral having explored the full range of movement:;

What this posture-movement awareness exercise does-

Lets you know if your back pain is caused by going into flexion or into extension.
Gets you to think about, and get a feel for, the safe middle range of your lumbar spine.

Comments
From your pictures, you can measure the ranges of movement for your lumbar spine, and compare them with approximate "normal" values below.

Measurement	Normal for the quadruped:- (approximate only!)	Picture to left:-
Lumbar flexion	20 to 25 degrees	22
Lumbar Extension	-10 to -20 degrees	-12
Neutral Lumbar Positioning	12 to -5 degrees	8

This 70 year old quote still holds true today: "Good body mechanics imply that all the joints of the body are used is such a position in relation to their total range of motion that the possibility of further motion in either direction - the factor of safety motion - is always present(2)".
Once you know the feel of the safe middle range, stick with it! - it gives you that "factor of safety!"

Reference

Quadruped flexion/extension is similar to "Hanah somatic cat stretch"
Shirley A Sahrman: "Movement Impairment Syndromes" Publ. Mosby, 2002 ISBN 0-8016-7205-8
Goldthwaite Joel E, Lloyd T. Brown, Loring T. Swaim and John G Kuhns: Essentials of Body Mechanics in Health and Disease. (1934,1952) Fifth Edition. Philadelphia: J.B. Lipincott.