Is it true that sex during the luteal phase can interfere with implantation of the embryo? what exactly causes this...orgasm, penetration, vigorous activity, etc? is there anyway to mitigate this other than total abstinence?

Cycle: Typical menstrual cycle lasts 28 days. The follicular phase lasts the first 14 days and there is a LH and FSH surge resulting in ovulation and the begining of the luteal phase. It is the days just after this that you are most likely to conceive. I am not aware of medical literature to support that factors such as vigorous activity interfere with implantation.