For a man carrying a nation's libido on his shoulders, Japanese porn king 'Shimiken' looks as fresh as a daisy.

The 35-year-old cult hero, described by one director as the "Cristiano Ronaldo of sex" and famed for his Herculean powers between the sheets, grins as he tells AFP: "It's a hard job, but somebody's got to do it."

Shimiken -- real name Ken Shimizu -- has slept with more than 8,000 women for his 7,500 movies, and recently caused a stir by begging for reinforcements, tweeting that there were more Bengali tigers alive than male porn actors in Japan.

"We're an endangered species," he said in an interview. "There are about 70 male actors to 10,000 women."

Shimiken's call to arms was retweeted thousands of times by fans worried Japan's $20 billion "adult video" (AV) industry could be under threat.

"We're getting rarer and rarer, like pandas," said the celebrity lothario, who drives a vintage DeLorean sports car -- the time machine in "Back to the Future" -- and carries phallus-shaped business cards.

"It is boring for viewers to watch the same actors all the time. That's the biggest worry."

Looking a little like porn's answer to British punk rocker Johnny Rotten with his spiky orange hair, Shimiken insisted he has the staying power to keep on going, despite making an eye-popping two to three films in an average day.

"Usually I sleep with two or three girls a day, so I have sex for about two hours every day," he chirped. "It's my dream job -- I've been doing this for 17 years and I never get bored of it.

"It beats working in an office," added the part-time bodybuilder, peeling off a t-shirt bearing the legend "Sex Instructor" to show off his biceps. "I'll do this until I'm 100."

He may have to, if the decline in male actors continues.

Fitness fanatic Shimiken follows a strict diet, and the contents of his sports bag reveal protein bars, packets of chicken tenderloin and boiled eggs, as well as Japanese reindeer supplements and a drink with snake extract to boost performance. But no little blue pills.

- Luxury treatments -

"I don't take Viagra," said the workaholic actor, who uses luxury face creams to keep his essential kit in tip-top condition, and boasts he has only once sustained an injury in the area -- when an actress accidentally damaged him with a stiletto. "I don't need it. Not yet."

Such is Shimiken's legendary prowess that actresses swoon at the mention of his name, but few express surprise that Japan struggles to produce more male actors.

"He's a stud," purred busty AV queen Anri Okita. "He's a marvel of nature, a genius. Male actors are a dying breed. It's a physiological matter. Only Superman can do what they do, to have that technique and stamina. Japan can be proud of them."

Shimiken puts the dearth of talent down to the fear of being found out -- or worse still, ridiculed.

"With social media now, there's the danger of being rumbled quickly," he said, confessing that his mother once walked in on a scene he was shooting. "Also they don't want to be compared to other actors."  

Many industry insiders blame the conundrum on a growing social trend known as "herbivore men": those who shun sex and traditional masculine values in favour of a quiet, uncompetitive lifestyle.

"Mentally, men have become weaker," said actress Yuko Shiraki. "They're less macho, less proactive about sex.

"Many men have lost confidence and can't express their feelings so there are fewer men coming into the business," added the 39-year-old, who used to work as a truck driver before switching to X-rated movies. "It's taxing on the poor male actors."

- 'Ronaldo of sex' -

Celebrated director Tohjiro, who goes by only one name, agrees Japanese men are going soft.

"I've been in this business for 27 years and you can see the increase in herbivore males," he said on a film set in Tokyo. "Men aren't hungry anymore. They've lost their desire. Everything’s on a plate for them.

"It wasn't like that for my generation," growled the 58-year-old. "If we got a banana or a pineapple we went crazy with joy. These days men don't get excited by anything -- the finest cookies or cakes. The same applies to sex and attitudes towards women and relationships. They just click on the Internet for it."

As Japanese men suffer from a punctured mojo, the tireless Shimiken continues to provide a beacon of hope.

"I do weights to be like Iron Man or Batman," he said, flexing his muscles before raising an eyebrow in comic hero fashion. "I am Sex Man!"

Shimiken's superhuman dexterity was put into perspective by Tohjiro, who pulled no punches when asked about the pressure of rising to the occasion on cue.

"Mental strength is the most important thing," said the filmmaker. "Actors have to perform under intense pressure but once you start to think about that pressure, it's over.

"Sex is difficult. It's just like with football. You don't see hundreds of (Lionel) Messis or Ronaldos running about, do you? It's the same thing. Only Messi or Ronaldo can score the goals they do."