Hán Xīngyuán (韓星垣)​ demonstrates Yìquán (意拳) Release of Power (發勁) and Tuī Shǒu (推手)

Spirit, Qi, Intention, Force, Coordinate to Become One (神氣意力，合一集中) from The Real Theory of Baguazhang (八卦掌真理篇) by Jiāng Róngqiáo (薑容樵)

神氣意力，合一集中

前面所說的精神、氣息、意識、力量等等各方面的鍛煉方法，它們並不是孤立的，而是合一集中的，不集中，動作就不能完整一氣，不合一，手腳就不能行動一致。所謂合一，就是手與腳合，肩與跨合，肘與膝合，神與意合，氣與力合，內與外合。所謂集中，就是這六合必須統一，和諧，協調，取得完整。

薑容樵

"All the preceding explanations on the spirit, energy intention and force are to be worked at the same time and should fuse with each other. They should not be practiced in isolation, they should rather be unified. If they are practiced in isolation, the movement cannot be unified, hands and feet cannot move as one. In the same way that and and feet need to coordinated, shoulders and hips need to be coordinated, elbows and knees are coordinated, the spirit and the intentioin are in harmony, the energy ant the force are in harmony, the internal and the external are coordinated. This called to focus, in other words these six coordinations unify in harmony and coordination, to obtain wholeness."

From the book Bāguàzhăng Practice Method (八卦掌練習法), by Jiāng Róngqiáo (薑容樵), based on the translation by Joseph Crandall

The Explanation of Taiji’s Proper Practice (太極正功解) by Yáng​ Bān​hóu​ (楊班侯)

太極下乘武事解

太極者，圓也。無論內外，上下，左右，不離此圓也；太極者，方也，無論內外，上下，左右，不離此方也；圓之出入，方之進退，隨方就圓之往來也。方為開展，圓為緊湊。方圓規矩之至，其孰能出此以外哉？
如此得心應手，仰高鑽堅，神乎其神，見隱顯微，明而且明，生生不已。欲罷不能。

"Taiji is round. Regardless of internal or external, up or down, left or right, it will not part from the circle. Taiji is square. Regardless of internal or external, up or down, left or right, it will not part from the square. Enter and exit with the circle, advance and retreat with the square; follow the square to the circle back and forth. The square is the root for opening and extending, the circle is the root for tightenting and compacting. The circle and the square are the established standards, what could depart this standard?
In this way, proficiency will be achieved, and it will go higher by looking up and get harder by drilling down, it will be subtler and subtler, appearing concealed but actually manifest, brighter and brighter, growing incessantly and continuing without end. "

Based on the translation by Yang Jwing Ming (楊俊敏) presented in the book Tai Chi Secrets of the Yang Style (太極拳楊氏先哲秘要)

Twin Pines, Level Distance (雙松平遠) by Zhào Mèngfǔ​​ (趙孟頫​)​

The Study of the Snake Form (蛇形學) from The Study of Xing Yi Quan (形意拳學)

蛇形學

蛇形者，乃天地所賦之性，身體最玲瓏，最活潑者也。身形有撥草之能。二蛇相斗，能泄露天之靈機，能曲能伸，能繞能蟠。在腹內卻為腎中之陽，在易即為坎中之一也，在拳中謂之蛇形。能活動腰中之力，乃大易陰陽相摩之意也，又如易經方圖之中，震巽相接，十字當中求生活之謂也。其拳順則內中真陽透於外，如同九重天，玲瓏相透，無有遮蔽，人之精神如日月之光明矣。其拳謬則陰氣所拘，拙勁所綑，身體不能活潑，心竅亦不能通靈矣。學者於蛇形中勉力而行，久之自能有得。如蛇之精神，靈巧奧妙，言之不盡。

孫祿堂

"The snake is endowed with the most nimble and lively body in nature. It is able to move through the grass. The view of two snakes fighting exposes the ingenuity of nature: it can bend and stretch, coil and curl. Within the abdomen, it is the Yang aspect of the kidneys. In the Book of Changes, it is one with the trigram Kan. In boxing, it is called the snake form. It is the ability of a movable waist and therefore it means the rubbing of the Yin and the Yang from the Book of Changes, looking like the interlocking of the Zhèn and Xùn hexagrams in the square diagram, the crossover at the center that represent the generation of life. If the boxing is performed conveniently, then the real internal Yang aspect will reveal itself outwardly, like the nine levels of the sky delicately passing through each other without obstruction, one’s vitality like the radiance of the sun and the moon. If the boxing is performed erroneously, the Yin Qi will be restrained, the clumsy Jin will be tied up, one’s body will not be lively and the mind will not be able to perceive clearly. Students of the snake form that persevere may grasp it after a long time, and as in the vitality of the snake, they will be nimble beyond words."

From the book The Study of Xing Yiquan (形意拳學), by Sūn Lùtáng (孫祿堂), based on the translations by Albert Liu and Dan Miller and Brennan Translation Blog