Is heavy lifting bad for getting pregnant?

I work at FedEx which is very physical. I do a lot of moving and heavy lifting for about 4-5 straight hours. It doesn't seem to affect my period at all, maybe by a day or so, so I believe I have a regular cycle. I'm just wonderIng if I were to conceive, would the heavy lifting affect implantation? When do I need to start worrying about lifting if I get pregnant? Thanks!