>>11479048google it bro. gave you enough terms to search for. type in 'athletic women hard to get pregnant' perhaps and '4th degree vaginal tear' and read. there should be lots of papers.
exercises mess up women's hormonal systems and menstruation cycles. my mom told me it takes up to a year to fix some if the woman's still under 30. above 30 and the women are infertile.
as for vaginal muscles.. squats make them too strong and a lot of the extra muscle bundles get created and they cannot hyperextend during the childbirth. so they tear all the way down to sphincter.... which also gets torn in 4th degree tears.
