What with the internet, all the stuff your mates are telling you and half-remembered nuggets of information from sex-ed classes, it’s hard to know what to believe when it comes to bedroom myths.

Luckily, FHM is here to sort fact from fiction, with help from none other than TV's Master of Science in Sexual Health, Dr Christian Jessen.

It is possible to enlarge your penis


You’ve always felt that you’ve been a touch below average since that girl from the year above laughed at you when you got it out down the park. Now, with the influx of emails for big-cock pills pouring into your spam folder and talk of penile enhancement surgeries, maybe it’s the time…

Dr Christian says: “It is possible. There are a number of ways. The least invasive is a technique called jelqing, which is kind of stretching your penis. But you have to do it all day, every day for about six months.

You can get penile stretching frames, too. You might not damage yourself, but if you’re really so obsessed that you’re willing to pull on your knob for six months, then there’s probably something else going on.

And then there are surgical options – injecting fat, which sort of works, and silicone. That’s a horrible effect. Those penis-pills emails are absolute bollocks, though.”

Girls get no stimulation from anal sex


It’s your birthday. You know what you’d like for your present, but you’re simply too shy to ask for it. Well, too shy and too frightened of getting a solid knee to the groin. Is “catching the A-train” such a selfless act on the part of your lady love?

Dr Christian says: “Not true – a lot of women do [get stimulation]. The clitoris has nerve endings that stretch quite far back – it’s not just a localised spot. You can get stimulation there as well as from the vagina. The sphincter muscles have lots of nerve endings, and that’s what anal sex is all about, the stretching sensation, so it can be pleasurable.”

Having sex before a football match will ruin your performance



So your Sunday-league manager has started telling you when you can and can’t have sex. So far, so creepy. The thing is, he’s convinced you’ll play better if you abstain from shagging. Could the tragic old pervert be on to something?

Dr Christian says: “Absolutely no scientific basis for this whatsoever. There’s no evidence that testosterone levels are lowered and aggression is therefore affected. None at all. Which is good news for sportsmen everywhere. Being more relaxed probably helps, in fact.”

Your nationality determines your penis size



The girl you’re seeing has everything. She’s funny, sexy, smart and well travelled. Maybe a bit too well travelled. She’s dated guys from France, Italy, Korea, Nigeria and somewhere called Micronesia. Naturally, this has you worrying about how you measure up to her previous flames…

Dr Christian says: “It is true, though most of the studies are flawed as they rely on self-measurement. But there’s a sense of average size. Places like Ghana, the Congo, Lebanon and Sudan come out above average, and countries like Korea, Taiwan and Thailand come out below. It’s genetic variation, related to the size of the women and criteria like that.”

Some girls are unable to orgasm


You tried ginseng. You've crated out the oysters. You bought a ground-up tiger’s penis on the internet and a special cream that gave you a rash. Nothing seems to be bringing your special lady to the point of knee-trembling euphoria, and you’re starting to think maybe it’s a lost cause…

Dr Christian says: “It depends on the definition. Ten per cent of women have never had an orgasm, but that doesn’t mean they can’t. There are people with a condition called anorgasmia who don’t seem to be wired in the right way, but some women may not have done so because they’ve not found the right way for them. It could be that of that 10%, maybe 1% or even less are physically unable.”

For all the rest of the sex myths, as well as input from FHM Girlfriend Lois and resident funnyman Daniel Sloss, grab the latest issue of FHM for just 399 pence.

*cm not inches...