Size has nothing to do with it.
Under water, no. You could bring up a typhoon with a pair of tweezers under water.
Above water is another matter.
My "buddy" for rescue weighed in at 140kg (300lbs). Even flabby after 10 years of not training and desperately in need of exercise I top out at 200lbs (naturally, it's all muscle!). I needed to take him out of the water using a fireman's lift. We were working in an area with about a 50m span of knee-deep water. I made it 1/2 way to shore with him and stumbled.
I fell face down in the water with him on top of me. I was pinned.
He did exactly what he was instructed to do.... pretend to be unconscious and comatose.
I...... on the other hand...... was suddenly realising that having a 300lb LARPer pinning you face down in knee deep water wasn't as much fun as it had sounded during the briefing!
I rolled over as much as I could and started tickling him! LOL
He rolled off of me and we both came above water giggling hysterically! It was really funny.
Years later we both took the IE together and can still laugh at at that "bonding moment".
But I digress. I can really imagine someone literally not being physically strong enough to perform a given exercise. It also made me realise that had this been real I would have drowned.
R..