User blog comment:SilencedSkies/Body Armor: A Comparison./@comment-4721065-20130211093014/@comment-4721065-20130213093401

Erm, WH40K is not a videogame first and foremost, but a Tabletop series. If you're talking about the recent WH40K: Space Marine here, than that is semi-canon at the VERY best (to put it simply, one Captain would never be capable of slaughtering anywhere near as many Orks as shown in that game). The fact remains that shoulder plates restricting the movement in any way is never shown in the lore, and given that it is fully powered, the most likely explanation is that the shoulder plates are lifted/shifted aside during the rapid movements.)

Regarding the nuclear battery, to say that it is fitted inside the backpack rather than the whole armour is splitting hairs at best, as that gives what, 3 extra cm of plating between the body and the battery? More importantly, however, is the fact that unprotected Imperial Guard can fight alongside the Space Marines and never suffer from effects of the radiation, meaning that it's protection is absolute.

Finally, the armour mode is only invincible until the suit runs out of power to sustain it, which would be about two seconds if the grenade explodes next to you. Given that WH40K bolters are 40mm rocket-propelled grenades, the suit would be finished after getting shot twice.