In America, baseball is a pastime. In Japan, it’s a martial art. Yakyu, or Japanese baseball, might look familiar, but don’t be fooled: while the rules are the same, under the surface Japanese baseball is a wildly different game. Just look at baseball manga like Kyojin no Hoshi (Star of the Giants), Dokaben and Major. While American players are judged by individual stats like batting average on on-base percentage, the Japanese focus on team-based plays like the hit and run, the sacrifice bunt and the suicide squeeze. Japanese managers are notoriously controlling; on some teams, players can’t change their socks without permission.

The biggest difference between the two games, however, lies in how the teams practice. In Japan, “spring training” starts in January, when the thermostat hovers around 40 degrees Fahrenheit. During the regular season, players often put in four-hour practices before games even start—extra work is considered a great way to beat Japan’s intense summer heat. At the amateur level, the intensity is even worse. Practices last from six in the morning to nine at night. Coaches hit players with bats and fastballs in order to build endurance. Once, at age 15, former New York Yankees pitcher Hiroki Kuroda was forced to run between the foul poles for four days. He had to do so without drinking a single sip of water.

While lawsuits have softened the culture in recent years, “training hell” remains a major part of Japanese sports culture, romanticized and codified by sports manga for decades. It’s a philosophy based on budo, or the traditional “way of war,” which states that suffering builds strength and character. It’s certainly not unique to baseball; sports are just the latest, most modern incarnation of centuries-old traditions.

When baseball first arrived in Japan in the mid-to-late 1800s, players were trained like soldiers. In 1854, the US Naval Commander Matthew Perry forced Japan to open its borders to America. Treaties with other Western countries followed. Soon, foreign advisors arrived to influence Japan’s military and education systems—and they brought comics and baseball with them.

The Japanese adopted both, and in doing so, made each their own. Artists like Rakuten Kitazawa, often referred to as the founding father of manga, fused American comic strips like Richard Felton Outcault’s Yellow Kid with traditional woodblock prints and 13th-century picture scrolls. When American teachers like Horace Wilson and Albert Bates taught their students baseball, the Japanese didn’t quite know what to make of it—team-based recreational sports didn’t exist in Japan—so they turned to what they already knew: the martial arts.

More than any other team sport, baseball plays out as a series of individual encounters, and baseball’s pitcher-vs-batter duels evoke the one-on-one showdowns found in traditional Japanese sports like judo and sumo. Japanese educators lauded baseball’s emphasis on patience, teamwork and self-sacrifice, and like martial arts, considered it an excellent way to teach students about traditional Japanese values like discipline, loyalty and respect.

This was especially true at Ichiko, formally known as The First Higher School of Tokyo, Japan’s first baseball powerhouse. According to Richard Whiting’s book You Gotta Have Wa, many of the students at Ichiko came from samurai families, and the practice routine the school developed was directly based on bushido, or the samurai code. In the military, Japanese soldiers underwent rigorous training in order to strengthen themselves mentally and physically. At Ichiko, the students approached baseball the same way. The baseball stadium became a dojo (literally; once, Ichiko students attacked an American teacher who scaled a stadium wall, claiming that he had defiled a spiritual place) and baseball became an art of war.

As per military tradition, Ichiko’s training regimen was incredibly demanding, and built strength through suffering. Team members lived in isolated dorms, far away from society’s distractions. Practices were so brutal that players peed blood when they were finished. Still, there’s no arguing with the results: in the first official baseball game played between the Americans and the Japanese, the Ichiko team won 29-4.

That success made Ichiko’s style of “bushido baseball” the norm, and it’s persisted through the modern day. In fact, traditional military-inspired training is so ingrained in Japanese sports that it’s become the foundation of sports-related pop culture, and these days it’s hard to find a sports manga that doesn’t contain some kind of reference to “training hell.”

In Ikki Kajiwara and Noboru Kawasaki’s Kyojin no Hoshi, a young boy, Hyuma, dreams of playing on the Tokyo Giants, Japan’s most popular professional team. He gets there thanks to his father, Ittetsu, who subjects Hyuma to long and brutal workouts. Ittetsu beats Hyuma regularly, and he humiliates the boy whenever Hyuma makes a mistake. At one point, Ittetsu forces Hyuma to wear a special harness, which builds muscle but makes Hyuma a laughingstock at school.

Yet, Kyojin no Hoshi isn’t a horror story: it’s an aspirational one. Readers admired Hyuma’s resolve, and the series (which was also adapted into a popular anime) popularized the idea that, like soldiers, perfect athletes are built through blood, tears and sweat. Professional baseball players in Japan often cite Kyojin no Hoshi as the reason why they got into baseball in the first place. Miami Marlins right fielder Ichiro Suzuki has compared his upbringing to Hyuma’s. Naturally, Ichiro’s father disagrees.

Kyojin No Hoshi set the template for every sports manga that followed, and training hell sequences appear in popular baseball series like Ace of Diamond, Major and Battle Studies (which is written and illustrated by Nakibokuro, a former student and player at PL Gakuen, home of Japan’s most successful high school baseball program).

Even gentler baseball manga, like Mitsuru Adachi’s various series, highlight the importance of training. Adachi’s work is often classified as romantic comedy, and his stories focus more on teenage romance than the ins and outs of a baseball game, but the sport still plays a crucial part in Adachi’s Touch, Cross Game and H2.

Touch, for example, tells the story of two twins, Tatsuya and Kazuya. Kazuya, the school’s ace pitcher, is driven and dedicated; by contrast, Tatsuya is a lazy underachiever. When Kazuya dies, Tatsuya must step up. It pays off; thanks to Tatsuya’s hard work, he ultimately leads his team to Koshien, or The National High School Baseball Championship of Japan. The Koshien tournament is Japan’s most popular annual sports event and one of the biggest amateur sporting contests in the world, and over the years it’s taken on a near-religious quality in Japanese culture. While Tatsuya’s training isn’t as brutal as Hyuma Hoshi’s, the underlying theme is the same: Tatsuya is only “pure” enough to stand on Koshien’s sacred infield after months and months of practice and sacrifice.

Training hell isn’t just limited to baseball manga, either. Eyeshield 21, which revolves around American football, and Slam Dunk, a basketball manga, also include hardcore training sequences. Unsurprisingly, training hell also appears in action and martial arts manga series. Annie and Eren in Attack on Titan both go through it. Bleach’s main character, Ichigo, is routinely beaten during practice. Dragon Ball takes the trope to an exaggerated, sometimes comedic extreme, as characters practice wearing hundreds of pounds of weights, or fight in training rooms with super-high gravity.

In manga, sports and martial arts even look the same. Compare the art in Shinji Mizushima’s baseball classic, Dokaben, to the action scenes in a title like Naruto. Both use thick speed lines and distorted figures to create a sense of violence and intense, perpetual motion.

Training hell isn’t pure sadism. In Japanese baseball culture, there’s a genuine belief that intense physical training instills traditional Japanese values like courage, selflessness and group harmony in players. Spiritual clarity accompanies physical strength. According to Robert Whiting, legendary Japanese coach Suishu Tobita once wrote, “The purpose of training is not health but the forging of the soul, and a strong soul is only born from strong practice.” That’s certainly the case in manga—and judging by Japan’s baseball success, it’s true in the real world, as well.