The effect of general physical activity and exercise training on the pelvic floor muscles (PFM), fascia and ligaments is not well investigated or understood. One hypothesis is that general exercise training, for example, jogging or strength training of the abdominal muscles, strengthens the PFM by simultaneous unconscious co-contraction. This may reduce the levator hiatus area (the opening in the levator muscles which allows for the passage of the urethra, vagina and rectum) and possibly prolong the second stage of labour, and thereby increase the risk of instrumental deliveries (caesarean section, forceps and vacuum).