I'm really curious about this theory. It states that men create more male sperm on average because male sperm is weaker as is a male fetus (so more male sperm is created to compensate). Male sperm is also quicker. Therefore if you have sex on the day of ovulation you are more likely to have a boy.
Alternatively, if you have sex around 4 days before ovulation, then the female sperm is more likely to 'stick around' as it is stronger and be picked up on the ovulation date.
For anyone who tracked their ovulation dates and pregnancy - has this been true for you? I've heard it a lot but want to see how often it works!