Quote Originally Posted by Cataphract_Of_The_City
In that case how exactly do you explain classical hoplites holding their 8kg shields with one hand for extended period of times?

Either you have a small shield that can be tied to your forearm (which would make neck straps superfluous) or you have a 60-75 cm shield that does need a neckstrap.
The argive shield as I said before had the rim exactly for supporting the extra weight on shoulder. The weight was making the first piece that a soldier running away would drop. From there comes the insulting characterization ''Ripsaspis (Ριψάσπις)''= shield dropper. You can also see an example of how soldiers complained about its weight in Xenofon when leading a unit uphill shouted to a soldier who was slow and he responded that its easy for him to say cause he is on horse back and carries no shield. Offcourse then Xenofon dismounted took the shield from him and started walking fast uphill until the insults of the whole unit forced the lazy soldier to take back the shield.