I can see the lower part of the arms flex when I stand on them, but also it's deflecting the chainring, so I think the whole assembly is ill suited to a 220lb, 300w FTP rider like me! I also get flexing out of the cheap, folding, plastic pedals, but after those flex, then goes the crank, so the whole thing is rather vague and unresponsive. On the roll, the chainring flexes enough to rhythmically rub the chain keeper when just putting moderate power through; I don't dare sprint on this bike, because I think I'd twist it apart!