25th century Shaolin was a style of fighting combining those of many races, including Klingon and Vulcan. Its base form was an ancient Earth practice passed down generation after generation. (Star Trek: 001: "When It Rains...)
As teachers passed on their techniques to students, they also passed on their inner Cal. The Cal itself had become a massive power, able to be tapped with the right know-how, and used during combat situations.