From the book:

For example, the term neijiaquan [internal martial arts] appears as early as Huang Pai-chia’s (Huang Baijia) seventeenth-century Neijia Quanfa (“Boxing methods of the Internal School”). However, it did not become a common classifier of martial arts styles until the nineteenth century, [i] and for practical purposes, not until Sun Lu-tang’s use of the term to characterize a category of martial arts based on “soft” power, in books published in the 1920s.

[i] However, there is mention of an “internal” martial art, and some literature describing the notion that qi energy could optimize the warrior’s potential in combat. These references date to at least the mid 1600s. Of particular note is Huang Tsung-hsi’s philosophical discussion regarding cultivation of qi energy (Tai-Chi Ancestors, p.41), the concept of coordinating the entire body (Ancestors, p. 43) and description of an “internal art” being counter to the brute force of Shaolin (Ancestors, p. 47). Huang writes: “Now there is another school that is called ‘internal’ which overcomes movement with stillness. Thus, we distinguish Shaolin as ‘external.’” As translated and quoted by Douglas Wile in Tai Ch’i Ancestors, p. 51. More on Huang in Section VII.

Adding to the discussion of disciplines purported to merge “internal energy,” or “qi cultivation,” with ancient Chinese yoga and martial arts in the mid-eighteenth century, Chang Naizhou (苌乃周) created a style that intertwined martial art with meditation, and which Professor Wile describes as “all but extinct.” (Ancestors, p. 71). Chang’s art emphasized qi development (Ancestors, p. 76), qi circulation (Ancestors, p. 77) –– insisting that stagnation can be removed by movement (Ancestors, p. 77) –– and emphasized the importance of focusing the body’s qi on a single point. (Ancestors, p. 78). More on Chang in Sections VII and VIII.