This has been used as an explanation as to why the creations don’t sport feathers like the real ones did, but maybe Rexy was born with incredibly strong bones, allowing it to run at unnatural speeds.
This is really a matter of physics and how much weight could be physically supported by the T-rex’s skeletal system, but at this point in the article it does feel prudent to remind everybody that the creatures in the Jurassic Park movies aren’t really dinosaurs.
It’s mentioned in the first film that they’re brought to life with the help of frog DNA plugging gaps in the genetic code, which makes them naturally different, but more importantly it’s noted in Colin Trevorrow’s Jurassic World that the prehistoric beasts aren’t actually made to be true to life, but instead the most crowd-pleasing forms of themselves.