Bit of a random question I suppose but here goes:
As a result of travelling faster and faster a body's effective mass will increase so the closer you get to the speed of light the 'heavier' it will become until the mass tends towards infinity.
It has been a couple of years so no derivation or proof I'm afraid but it is part of Einstein's Special Theory of Relativity.
Think of it as trying to lift a dumbell above your head, and the closer you get to locking out your arms people keep piling on weights on the side making it more and more difficult to go up another inch until you get to a tiny distance before locking out and then the mass of the dumbell suddenly increases really quickly becoming effectively infinite making it impossible for you ever to lift it fully.