Was Grade III physically slower or did the bulky body just limit movement?

[nickzambuto]

Personally I think the big muscles were mainly what was killing this form. We know it had much greater ki than the other Super Saiyan forms, so it wouldn’t make sense for Trunks to become physically slower. He had much more ki therefore more ki output to his speed. How can the increase of ki make his speed go down?

For example, Grade III Trunks might have been able to beat Perfect Cell in a race, with his explosive ki propelling him much more powerfully. But the point of the fight was that Trunks can’t physically move well anymore, and it was like a huge bodybuilder who can’t even reach his back because his muscles are too big, trying to fight a real martial artist in Cell.

[theherodjl]

Since there are a million other instances of characters getting stronger and faster by transformations/states that involve physically bulking up, I'm willing to bet SSJG3's issue is that it's larger muscles merely hinder movement. The Saiyans are very accustomed to fighting with their natural muscle mass so making their muscles huge probably throws off their balance and general coordination with striking. It might be possible to overcome the issue by getting used to fighting with large muscles but I don't think the Saiyans care enough to do so, not when they have stronger & better transformations.

[Lionel]

To be honest, when you look at Goku's musculature back in the Freeza arc as a Super Saiyan and compare it with Grade III, the difference isn't all too great. Something about the state itself seemed to place a disproportionate emphasis on physical power over speed. Could it have to do the ki amplification going towards that trait specifically?

[LoganForkHands73]

I believe it's a combo of both? Even though Dragon Ball is perceived as being all about abstract, metaphysical stats, SSJ Grade 3 being so unnaturally bulky and overmuscled is used as a visual indicator of what the form is all about -- speed sacrificed for raw strength. I mainly agree with OP that the strained musculature is the main impediment. We also see in Super that Caulifla moves clumsily when she tries to use the form.

[miguelnuva1]

It limited movement and drained stamina too quickly. That works better off everything we are shown in the Manga and the anime.