You will sometimes encounter in martial arts training, something which the Japanese refer to as Shuugyou Renshuu, or austere training. In Kyokushinkai karate, for example, they have the famous 100 man kumite. In this type of event, the participant will fight 100 full contact rounds, consecutively against fresh opponents. The founder of Kyokushin, Mas Oyama, was known to go an an annual retreat to the mountains where he would do nothing but practice meditation and karate for months on end. Below is an excerpt from an article on austere training as practiced in a modern day dojo. If you click on the title of this post, you'll be directed to the full article.
Shugyo Renshu by Nathan Scott
Shugyo (修行) may be defined literally as "conducting oneself in a way that inspires mastery". While the meaning of the kanji used in "shu" was originally translated as 'using a brush to strike away the dust that obscures the viewing of a persons original elegance', the combined kanji of "shu" and "gyo" (carrying out, walking along) is now generally translated as simply "severe or austere training". The kanji rendered for this version of "shugyo" is most commonly associated with Buddhist asceticism, and most notably, the "shugenja" (修験者, ascetic mountain-dwelling monks).
In addition to ascetic Buddhism, the act of shugyo can be applied to any serious endeavor or "michi" (path). For example, the term "musha shugyo" (武者 修行, an exponent of martial [arts] conducting themselves in a way that inspires mastery) refers to a "knight-errantry" tour, a practice of travelling around the country in order to train and test their martial skills that was followed by many serious budo-ka of pre-Meiji Japan (and to a lesser degree post-Meiji). The kanji used in the term "shushi" (修士, master) also combines the same shu character with the character for "man" (alternately read as "samurai"). The implication of this kanji combination is that the person, and perhaps only the person, that follows the way of austere training can obtain the skill level of a "master".
A related term worth mentioning is "kugyo" (苦行), which translates literally as "carrying on while suffering", and is understood functionally as referring to asceticism, penance, or mortification.
In centuries past, shugyo were periods of time where the adherent (usually certain types of monks or warriors) would submit themselves to extreme conditions - mentally, spiritually and physically, in order to achieve certain enhanced or enlightening experiences. This was viewed as an important forging process that, among other things, taught one what their actual limitations were; or more appropriately, what their lack of limitations were.
There are several well known shugyo-sha (修行者, practitioner of austerities) that are known to have followed such severe training in more recent years. The famous Karate-ka Mas Oyama was known for his long periods of mountain training.
Tesshu Yamaoka was one of Japan's most famous and interesting swordsmen. Tesshu was influenced by Zen, and eventually founded his own tradition called "Itto seiden muto ryu" (the tradition of no-sword), perhaps partially in reaction to the dissolve of the warrior class in 1868. Though he was also an exceptional artist, and created over a million pieces of calligraphy in his lifetime, he gave money to others his entire life and died a poor man.
It is said that Tesshu required his disciples to follow a progressively strenous physical trial, that would have been considered brutal even in his own time: