A difficult vaginal birth is known to be one of the causes of damage to the pelvic floor muscles. Prolonged second stage of labour is thought to be one of the implicating factors in this damage. If the muscles of the pelvic floor were hypertrophied in response to repetitive high impact training, then the 'suspected phenomenon' of a more difficult childbirth for very athletic women might be related to these muscles reducing pelvic floor compliance.
