Are your hip flexors weak?

Comparison of anteroposterior thickness of elite sprinters and distance runners’ abdominal muscles…

http://209.85.229.132/search?q=cache:hC5V6I61PgUJ:journals.mui.ac.ir/jrrs/article/viewArticle/2773+running+sprinting+abdominals&cd=3&hl=en&ct=clnk&gl=uk