Every Day.
For example, I met a 15-year old boy today who had what appeared to be very minor friction burns on his right hand and a growth in his bicep.

And he'd come in with his Mum.

I managed to get Mum to leave the room and discovered that on examination of his genitals - to no-ones surprise - he'd been masturbating himself silly, thus causing an unnatural growth which his Mum (in over-protective-mother-hen mode) had mistaken for a tumour.

Explained to Mum that he'd been exercising a little too much and that the growth in his arm would steadily reduce over time given that he was sporty and exercising regularly.
(Medical_Male Say aaaaaaaaaaaaaaaaaah, Thu 21 Jan 2010, 16:51, 3 replies, latest was 16 years ago)

hahahahahahahaha

( Vipros. clever got me this far, then tricky got me in, Thu 21 Jan 2010, 16:51, Reply)

pffft

how much would you need to masterbate to do this?
( Naked Ape call me Caitlyn, Thu 21 Jan 2010, 16:53, Reply)

relentlessly I'd say

( Vipros. clever got me this far, then tricky got me in, Thu 21 Jan 2010, 16:57, Reply)

I see a word forming…
its in great big flashing neon lights… it says… Challenge
(Flim-Flam the Magnificent "You is talking loco and I like it!", Thu 21 Jan 2010, 16:58, Reply)

haha, awesome

( Vipros. clever got me this far, then tricky got me in, Thu 21 Jan 2010, 17:02, Reply)

I once saw this documentary about OCD

and a guy on that was talking about how much he wanked,

"usually I'll masterbate around about 5 or six..." at this point I thought 5 or 6 wanks is a lot for one day but not completely out of the bounds of normality, "hours a day" he finished :s
( Naked Ape call me Caitlyn, Thu 21 Jan 2010, 16:59, Reply)

christ
either he's got a fucking lot of staying power, or massively capacious balls and the ability to produce spunk at a hell of a rate.
( Vipros. clever got me this far, then tricky got me in, Thu 21 Jan 2010, 17:03, Reply)

Surely after hours that amount of friction would create a fire?!

(Flim-Flam the Magnificent "You is talking loco and I like it!", Thu 21 Jan 2010, 17:04, Reply)

God knows

Maybe he did it sitting in bath of lube...
( Naked Ape call me Caitlyn, Thu 21 Jan 2010, 17:05, Reply)

that's the only way I reckon
either that or he was just doing it wrong
( Vipros. clever got me this far, then tricky got me in, Thu 21 Jan 2010, 17:06, Reply)

How do you know these things?
Haha
(Flim-Flam the Magnificent "You is talking loco and I like it!", Thu 21 Jan 2010, 17:06, Reply)

Just a guess honestwrgv
sorry about that hand slipped...
( Naked Ape call me Caitlyn, Thu 21 Jan 2010, 17:12, Reply)

To Add A Bit Of Information ...
1. Reduced risk of fire - not much nylon about, apparently

2. Averaging 6 - 8 times a day, each taking around 8 - 10 minutes

3. Averaging orgasm 2 - 3 times a day

4. Marginally increased risk of TIA / stroke through massive increase in blood pressure
(Medical_Male Say aaaaaaaaaaaaaaaaaah, Thu 21 Jan 2010, 17:25, Reply)