"Marie Stopes had championed her ‘Pro-Race’ version of the rubber cervical cap because the diaphragm ‘must be worn so as to cover the whole of the end of the vagina and depends on stretching the vaginal walls to stay in position…[so] certain movements of physiological value (particularly to the man) which ideally the woman should make are then impossible’. Van de Velde agreed with Stopes that the diaphragm limited vaginal movements but he commented dismissively that most ‘women to-day are not able to operate their pelvic muscles voluntarily to the best advantage in coitus, so the inability to do so would not represent any appreciable loss to them’. It is possible that the sexual upbringings of women over generations ensured they were unaware of the range of movement the muscles associated with vagina were capable of."