The world record for the deadlift in the 148-pound weight class is just over 700 pounds, whereas the world record for the 308-pound weight class is 939 pounds. Doubling the weight class does not double how much a man can deadlift; it only increases the amount by about 30 percent. That is a dangerous tradeoff because large muscles require more oxygen to function, and if you are working so hard that you cannot replace that oxygen fast enough, you will go into oxygen debt.