>>76359000 (OP)Gravity training the way goku did it is great, he slowly increased the gravity overtime (but to be fair he cheated by having magical roid beans that heal all injuries and restore stamina).
Vegeta is a retard because Goku worked up to 100 times gravity but vegeta ramped it up to 400 from the start, trained to absolute failure and spend a lot of time hardly making any gains because he was a fucking retard.
Also, astronauts, f1 drivers and military pilots experience g forces which is literally having multiple times gravity, for example f1 drivers can experience up to 5 forces on sharp turns wich make their head feel like it weights 45kg so they train their neck side flexion to resist pulls of 50+ kg but this is during sharp turns idk how it would work in a constant steady state but basically yes humans can handle multiple times normal gravity albeit those that do are in specific scenarios.
That said regular strength training would be more effective to train you for higher gravity forces than having a gravity chamber because your muscles will be forced to produce twice the amount of force for every 1g force increase so lifting heavy would be easier to perform.