The longitudinal back of the Icelandic Horse can be conformed in many different ways. It can be relatively straight, or slightly concave, to very concave; strong, tight, medium tense (essential tension), to very weak, or lax; and / or a combination thereof.

Some backs cannot carry much weight; some are stronger than others.

Some are flexible; some have too much laxity.

It will depend on many different things as to whether the horse's back can support a certain amount of rider weight, and how that weight will affect the back.

Some backs will sag quite a bit and take the horse's back into ventroflexion.