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I don’t think so, no but, allow me to explain why!

Firstly, I’m going to use this art drawn by Horikoshi here:

I want to thank @ukitakejuushiro for this post  because they made a very good point here. Aizawa, is holding Bakugou down with literally one arm and absolutely no strain, while Bakugou himself is struggling to get Aizawa’s grip off of him. That’s not the only thing I want to point out here though. 

Notice where Bakugou’s left hand stops against Aizawa’s forearm. 

That’s a thick ass arm, my dude. Bakugou can’t even wrap his hand around Aizawa’s wrist fully. I know Aizawa looks skinny because he wears a baggy ass black suit as his hero attire and they made him appear like a twig in the anime, but legit this man is beefy. Horikoshi basically confirmed this for us every single time he’s ever drawn Aizawa in fitted clothing. 

Aizawa is a broad guy. He is thick. He isn’t a a twig like his loose-fitted black suit would have you believe. 

Look at that fucking neck and those shoulders! Also note how wide his waist is and how thick his wrists are. 

This is a reasonably buff dude. Which shouldn’t be all that shocking considering he can run across power-lines like it’s the easiest thing in the world to do and also dead lift a soaking wet Deku with one hand like it’s nothing. He has the physical prowess of a gymnast combined with a mixed martial arts fighter.

This isn’t my only point though. Look at All Might:

All Might is a god damn mountain. He’s ENORMOUS. But Aizawa in the hero swap:

He is nowhere near as huge. He’s not even close to All Might’s size here. He’s the exact body type you’d expect from someone who is as physically inclined as he actually happens to be. Also notice that his neck and shoulders aren’t any wider than they’re normally drawn WITHOUT HIS CAPTURE WEAPON ON. That’s another thing you have to take into consideration here. His hero outfit does literally nothing in terms of granting people a nice view, ya feel me? It’s baggy af and his bondage scarf usually covers his shoulders and entire neck. So what we see here is all just for more defined because he’s in a skintight body suit instead of a loose tracksuit with miles of metal woven cloth wrapped around his neck and shoulders. 

The last thing I want to add is this:

For every other character Horikoshi has done a costume/quirk swap for, no one’s body type changed. Not one. I get All Might can go back and forth between buff and slim, but I feel like if Horikoshi drew Aizawa to be buff for the sake of portraying All Might, he would have given Aizawa the full All Might, mountain sized body. Not just a beefed up version of himself. Especially since he hasn’t done that for any other character. I mean, Bakugou is Nomu in the very same art but he is no taller, and no buffer than his usual body type. He’s just shirtless.

So I believe that is actually Aizawa’s true, canon body. You just get a much better view of it because the All Might suit is like a second skin :D