Pattern help increasing stitches

Hi there,

In need of more help with the jumper I’m knitting. I’m on the sleeves and I’m confused by the increases… I understand that I need to do an increase at both ends in rows 3,5 &7 according to the pattern however I’m then confused by the instruction “then on following 4th rows”. I don’t know what counts as the 4th rows? Can anyone help?

For the first size for example, you have 49sts. Increasing on the alternate rows would be 3, 5 and 7. The following 4th rows are rows 11,15,19,23,27,31 and so on.