SV Standard No. 166 reads:
"The upper line runs from the base of the neck via the high long withers
via the straight back towards the slightly sloping croup"
Progressive developmental changes of significance in the GSD backline:
1 - Straight spine > low anticlinal spine height, withers long, sloping and highly defined against the thoracic and lumbar back, high hip and knee height position, normal pelvis angle, tail does not make contact with the ground.
2 - Rise in spines anticlinal region > back slightly/curved and withers definition less sloping/defined against the thoracic back, hip slightly lower, pelvis slightly more inclined, tail just makes contact with the ground.
3 - Rise in spines anticlinal region and downward curved lumbar spine, withers definition less sloping/defined against the thoracic back, lower hip and knee position, pelvis inclined, tail makes contact with the ground. Curved spine.
4 - Rise in anticlinal region and downward 'straight' lumbar spine > back decidedly curved, withers definition level and ill- defined against the thoracic back, peak visible to backline at T13, hip and knee closer to the ground, pelvis inclined, tail makes contact with the ground. A form of canine spinal kyphosis.
Anticlinal region of the spine
Please note: these are key point changes that can be viewed as forks in the developmental road. There are minor roads that branch off these and to understand the matter in full I recommend reading the following article that this leader item comes from; The Back of the German Shepherd Dog - development, structure & function