Many martial arts can take decades to master. Some traditional arts, like karate, are balletic in nature. Others, like Thai boxing or jiu-jitsu, are more pragmatic for self-defense or prizefighting. All have techniques that display beauty, grace, and agility.

Others simply require you to endure getting hit in the testicles.

Recently, a Chinese kung fu practitioner named Wang Liutai received media attention for his prowess in absorbing blows to his crotch without any apparent injury, even inviting a partner to swing a giant wooden log into his midsection.

Other martial artists, like Wei Yaobin (below), have also demonstrated an ability to withstand blunt-force trauma to their groin, eagerly smashing bricks into their bits without screaming.

The skill, while undoubtedly impressive, seems contrary to what’s known about the soft tissue of the genitals and how a powerful strike should prove both incredibly painful and traumatic.

So how can these individuals do it? What’s the secret to avoiding a ruptured testicle?

Michael Kelly, DO, a sports medicine specialist and ringside physician for mixed martial arts contests in New Jersey, has studied Eastern arts with an eye on their applicability in the context of what medicine knows about the human body. He’s seen the footage of Liutai and others and tells Mental Floss that, practically speaking, the guru should have ground hamburger for genitals after smashing them with a log.

“It’s not really some sort of skill you can develop to prevent injury to the testicles,” Kelly says. “If you look closely at the videos, he brings his inner thighs together. He’s distributing the force over a wider surface area by using his abdominal muscles as he moves forward.”

According to Kelly, it’s possible such feats are accomplished by tensing the adductor muscles in the thigh, which connect to the testicles. By squeezing, Kelly says, the martial artist can create a “tensile net” that might better absorb force. But even that would be painful, and very likely cause injury.

“That type of force on testicular tissue would cause damage,” he says, up to and including a testicular rupture or bruising that could put pressure on a vein and result in tissue death.

Martial artist Wei Yaobin gets kicked in the crotch repeatedly in Luoyang, China.New China TV, YouTube

One other possibility is that those receiving such blows are voluntarily activating their cremaster muscle, which would allow them to retract their testicles into their abdomen. Normally, men do this involuntarily to some degree when their testes are confronted with cold weather or stress. But that doesn’t typically involve the testicles going all the way up. "There may be an element of training to try and pull them closer," Kelly says. "Or maybe it’s a combination of the two."

Although Liutai has expressed an interest in teaching what he’s dubbed “iron crotch kung fu,” it’s likely that such techniques only work under certain circumstances.

"I’m willing to bet if I put the guy on an exam table and hit him with a reflex hammer in the testicles, he wouldn’t be able to tolerate it," Kelly says.