Under-thrusting diaphragms

A latex All-Flex arcing spring diaphragm was best for under-thrusting

Under-thrusting play: On another forum there was a recent discussion of a method of under-thrusting that involves using a diaphragm that is a size too large. I suppose in some limited circumstances that might be possible. However, for the maximum comfort of both parties I think for under-thrusting play a diaphragm at least one size (5mm) smaller than the size a woman needs for contraception should be used. The Ideal style diaphragm for under-thrusting play was the latex Ortho All-Flex arcing spring. However, Ortho switched from latex to silicone for its All-Flex in the fall of 2008 and stopped making the coil spring rim style entirely so the few of us who still have a latex All-Flex in good condition are fortunate indeed. The 70mm latex All-Flex shown in the photo accompanying this post is two sizes too small for me and is the size I use for under-thrust play. As I’ve mentioned before a latex dome is stretchier and has much better heat transfer properties so it’s much more fun to use than the newer silicone All-Flex. And for those fond of the rubbery/fishy scent of a diaphragm that has marinated in vaginal and cervical fluids during a lengthy insertion (more than 24 hours) a latex dome has a much stronger odor than does silicone. The scent of old semen discharge adds to the stench which some vaginal fetishists find intoxicating.

An under-thrust study: A few years ago I participated in an under-thrusting study while wearing correctly sized [rather than a size or two smaller] and properly positioned diaphragms of all the available rim styles – Arcing, coil and flat spring with both uncut partners of very large girth and more normally equipped men. With the latex All-Flex (the easiest rim style to under-thrust) for the large girth men it was uncomfortable for both of us. Those encounters were part of a study my women’s clinic conducted to see which rim style put the wearer at the greatest risk of having her diaphragm accidentally under-thrust while using it for contraception during vanilla sex. All the women participating in the trial had deep post-pubic vaults as most women do. women with shallow or no post-pubic vaults aren’t good candidates for effective diaphragm use because the anterior rim is positioned where it may hurt a partner during vanilla sex and is easier to under-thrust than if the woman had a pronounced/deep post-pubic vault.

The results of the study showed that the easiest to under-thrust was All-Flex (arcing), then Milex Omniflex (coil) and Semina (coil) of similar ease. Then Milex Arcing and the most difficult was Reflexions flat spring. The Milex Arcing is more difficult than the All-Flex because it folds with two elbow hinges so the rim has to be positioned exactly right for a thrusting penis to cause it to fold. The switch from latex to silicone has not changed the study results. Of course no diaphragm is risk free since acute angle brute force thrusting can stretch the vaginal wall to allow a penis under the rim even of a Reflexions flat spring.

Penetration depth: In missionary penetration depth can depend on the shape of the couple’s pubic bones making standard missionary unlikely to attain deep thrusting unless the male partner is very well endowed. During the trial when I was taken in missionary all of my uncut partners of very large girth came away from their encounters with sore or sometimes raw frenulums. One was in so much pain he lost focus and couldn’t finish. With one or both partners having prominent pubic bones it may be necessary for the woman to put her legs on her partner’s shoulders to give him the depth to reach her cervix and the thrust angle needed for under-thrusting. I have a prominent mons veneris and at that angle I had to use lubricating gel on my labia to prevent perineal tears that less experienced women in the trial were having. It was a tiring and not all that pleasant experience.

Doggie style was somewhat better - wasn't nearly as traumatic for the men, but for me having the rim forced into my posterior fornix when he’s trying to get under it was still uncomfortable. While still tight there was more room between the back of my pubic bone and the rim (because on my elbows and knees my uterus and cervix are pulled deeper into me by gravity) for him to get the smooth top of his glans under it. And of course because of the gravity effect I could take a longer man more comfortably. Doggie is certainly the preferred position with a well endowed partner because his frenulum caresses my G-spot while his tip thrusts into my cervix.

Again the above results were for large girth men with the woman wearing a correctly sized diaphragm. For a man of more normal size the order of ease to under-thrust didn’t change, but the men suffered less physical damage. With a too small diaphragm you get all the pleasures of under-thrusting while lessening the discomfort and possibility of damage to your male partner(s). The only down-side of using a too small D is that for some women it may be difficult to remove afterward.

Under-thrusting, an explanation

A vintage Kirby Morgan Mk 16

Foreword: This under-thrust explanation is being written in reply to a comment posted by Eric on my entry for November 24, 2010 entitled “Under-thrust training” in which he wrote: “I've never understood how someone could thrust around it. Of course, I would think something like that would have to be a fluke or someone would have to have a lot of skill. However, you might've mentioned the possibility of poorly-fit diaphragms.” An explanation requires some detail so I want to post it as a blog entry rather than a comment so more readers will see it.

Under-thrusting defined: What I’m talking about is the intentional under-thrusting (forcing the tip of the penis under the rim) of a diaphragm worn for contraception and/or upper reproductive tract protection. Under-thrusting of a contraceptive diaphragm is far more likely during vanilla sex if the diaphragm is too small, but it is fairly rare if the diaphragm is properly sized and correctly inserted because the male partner is almost always interested in giving his partner her pleasure first or just getting off himself and most guys I’ve been with are trying to reach my cervix and none of those goals are easily accomplished by acute angle thrusting of the male penis which is necessary for successful under-thrusting.

Arousal: There are two factors that will determine the ease with which a correctly sized D can be under-thrust. First is the degree to which the woman is aroused. That matters because when fully aroused a woman’s vagina will lengthen (called tenting) by 5 cm or more (depending on the woman) as the uterus and cervix are pulled up and back out of the way of a thrusting penis. That means that the anterior rim of the diaphragm will be pulled out of the wearer’s pubic notch at least to some extent so there may be a gap between her pubic bone and the anterior rim of her diaphragm.

Missionary position: A few minutes after correct insertion the dome of the D should have developed a seal against the anterior wall of the vagina so the rim should not drop down unless the seal is broken, but if the woman is on her back and penetrated in missionary, if her partner thrusts up at an acute angle (into her anterior vaginal wall) when she is fully aroused he may be able to push his way between her pubic bone and the rim and thrust beneath it. Then he is inside the dome and if he ejaculates sperm is placed against her cervix. That’s why spermicide is used as a back-up.

From behind: When the woman is taken from behind while bent over so she is penetrated doggie style, the gap (after tenting) between the pubic bone and the rim of the diaphragm is even larger. That’s because the uterus and cervix are pulled deeper still by gravity when the woman is on all fours or standing bent over with her hands on her knees. With his partner in that position the man has to thrust downward at an acute angle if he is going to try under-thrusting his partner’s diaphragm. Even with a correctly sized diaphragm and during vanilla sex because the rim can be pulled so far out of the woman’s pubic notch it’s in this position that there are the most complaints from men about hitting the rim, which is uncomfortable for most of them.

Rim Style: The second factor that determines the ease with which a diaphragm can be under-thrust is the type of rim (coil, Arcing or flat spring) of the diaphragm the woman is wearing. There are practical reasons for a woman to wear an arcing spring or a coil spring rim, however both the arcing and coil spring rims are easy to distort when thrust into at an oblique angle without much indication to the woman that it is happening. That is not the case with a flat spring rim.

The only way a flat spring rim will compress is when it is compressed in the plane of the rim, thrust into edge on not at an angle to the plane of the rim. Therefore, when the rim is hit at an oblique angle as it almost always is the rim will not compress and it’s like hitting a metal wall. The penis will drive the uncompressed rim painfully into the woman’s vaginal walls alerting her that her partner is doing or trying to do something he shouldn’t. And ramming a flat spring rim that way will be painful for both partners.

The arcing spring rim is the most popular with doctors because it can be worn by women with a wide range of vaginal muscle tone and it is easier to insert correctly. However if the woman needs a menstrual gas guard that can be used effectively during dives deeper than 30 feet and one that is difficult to intentionally under-thrust then the flat spring Reflexions is the only one that meets those criteria. There are a few men in Vegas who are masochists and sadists and these are the guys who will enjoy the pain of trying to under-thrust a flat spring diaphragm and enjoy hurting his partner and perhaps impregnating her. But if they try she will certainly know what he is doing.

Tradeoffs: Ideally, except for when a woman is on her period a cervical cap would be the best barrier to wear for dive-sex as it can’t be under-thrust and if correctly fitted it is very difficult to dislodge with a thrusting penis. The problem is that for petite women or women in their teens their pelvic anatomies may be too small to be fitted with FemCap (the smallest is 22 mm) and quite often their partners are hurt by hitting the removal strap or if that has been trimmed away the dome and find it uncomfortable. So a latex Reflexions flat spring diaphragm is probably the best all around gas guard available for petite or very young women.

Sex in a Kirby Morgan

In the Pit: On Thanksgiving Day while my other guests were watching football I took Adolph to the bottom of my 68 ft deep pool, the pit. He isn’t interested in American football and he wanted to see what it would be like if we both wore surface supplied Kirby-Morgan 47 helmets. I was CD7 and we both enjoyed ourselves. He is something of a sadist and I’m a masochist so when he battered my cervix through the dome of my Reflexions he actually hurt me enough to bring on a cervical orgasm which was awesome! He was bouncing me around pretty severely, but with chin strap, fitted head cushion, neck pad and the neck dam/neck ring assembly and twin-pin locking collar to hold the helmet securely in place I was quite safe, not in nearly the danger I would have been in if I had been wearing a KMH 16 [shown in the image at the top of this entry] where the latching assembly could be unexpectedly broached and have the helmet separate from the yoke assembly. I wouldn’t say the KM 16 is unsafe, but the latching mechanism that holds the helmet to the yoke and neck dam is an obsolete design more than 30 years old.

The KM 47: Adolph and I helped dress each other in our KM 47s so I got to pay close attention to how it should be done. It was a bit of a struggle though we put on the helmets standing on the shallow ledge so we could just submerge after we locked ourselves in to get rid of having the heavy helmet on our shoulders as quickly as possible. If I’m being thrown around during an intense sexual encounter I’m a lot happier with the much more secure latching assembly of the KM 47 holding the helmet sealed. I love the way the head cushion snaps into the helmet shell and can be custom fitted to make sure I could get my long hair (in French braids) comfortably and safely contained in the helmet. With everything fastened properly (including the chin strap) I felt snug and safe in my KM 47. The helmet’s weight is about 33.5 lbs and mine has been adjusted with weights for balance and neutral buoyancy in fresh water. A drawback of the KM 47 (or any KM mask or helmet) is that there is limited visibility through the polycarbonate lens when compared with my Ocean Reef Space Raptor FFM and because of the helmet’s size there is inertia as the diver turns her head.

But the reduction is visibility was offset in my case by the head protection the fiberglass and carbon fiber shell and head cushion provided when Adolph repeatedly shoved me into the wall during our encounter. When I tried to stay against the wall he would pull me away and then shove me back so the back of my helmet was repeatedly slammed into the pool wall as he thrust into me. I wouldn’t have escaped w/o a concussion if I had been wearing only a neoprene hood and FFM. But that’s just the way Adolph is. He extremely strong and goes after sex with a woman with amazing intensity. He knew better than to try and under thrust my gas guard though it is one of his fave tricks with most of his other partners. I would say he was brutal if I hadn’t enjoyed our encounter so much.

SILCS diaphragm - under development

The single-size (70 mm) SILCS silicone diaphragm

A reader’s query: This was posted as a reader’s comment and my reply on my October 23, 2010 Entry “Gas guards for high school girls”. It concerns a new design for a cervical barrier that still has to be approved by the FDA. I haven’t discussed SILCS before so I thought I would re-post this discussion where more readers can read it.

The reader wrote: “SILCS is an intravaginal barrier device currently under development. It is made of silicone with an arcing ring. SILCS has a pre-shaped rim to cling high in the vaginal vault and a finger cup on one edge for easy removal. It will be a one-size-fits-all device. I would appreciate your expert opinion on this new contraceptive Diaphragm. http://www.path.org/projects/silcs.php”

My reply: Actually, SILCS is a single size (70 mm) one-size-fits-most device of advanced design. I like the design, but I hate the fact that it will be available in only a single size. Current thinking is that SILCS may be available as early as 2011. The FDA has yet to approve it for use in the U.S. I am very skeptical about the effectiveness of one-size-fits-most contraceptive devices.

The intention of PATH is to develop a simple inexpensive device that poor women in under-developed countries can use without the attendant costs of medical providers, pelvic exams and fitting visits and in this they may be successful. The four most prescribed diaphragm sizes in the U.S and Europe are 65 mm, 70 mm, 75 mm and 80 mm. Currently diaphragms are made in sizes from 60 mm to 90 mm.

That SILCS will only be available in a single 70 mm size is worrying. A single 70 mm size is too small in a traditionally shaped diaphragm for many women and using a too small device would decrease its overall effectiveness for users. That’s because a traditionally shaped diaphragm that is too small will expose the anterior rim to the likelihood of being thrust underneath by a partner’s thrusting penis. With the penis under the dome at ejaculation sperm is deposited against the cervix protected only by the spermicide which should be applied in the dome. The curved relief arch (on the anterior rim) of the SILCS design may (or may not) go some way to minimizing the problem of under-thrusting, but we won’t know about that for years.

I have no doubt that if SLICS becomes easily available in under-developed areas where it will give women something to use where previously they had nothing, then it is a major step forward. I’m not at all certain that it is as good as or better than a properly fitted and correctly inserted traditionally shaped diaphragm.

SILCS showing the curved anterior relief arch