A single lineage can have both Jedi Knights and Sith Lords. A quick way to spot a Sith is the breathing. If you can hear the breathing on the exhale, it is a Sith technique. This is true for the internal schools. (The external schools sometimes coordinate a strike with a fast vocalized exhale which serves to condense the body into a single unit. Great. Different school. Different fruition.)
The internal schools have to be able to separate the breath from the movement or they can not achieve speed. The big confusion happens because Sith are seduced by power, particularly power that comes up from the feet (yin/darkness). This is an illusion, but most people are fooled by it. When I say most people I am not including people who use force to physically coerce people or animals as part of their job. They are harder to fool.
The Darth Vader compression breath is most common where people teach Qigong, obviously, since that is mostly a Sith lineage. Darth Vader breathing infuses qi into the body where it mixes with jing and makes it harder to move. Many yoga schools use it for that reason, they want you to hold the posture. That is why the Sith schools are so concerned with getting the Qi to flow throughout the body. When qi is stuck inside and mixed with jing, the only way you can move is by flow. It is a self-fulfilling prophecy. Often Sith lineages are obsessed with "rooting and yielding," in other words, death.
The Jedi goal is to make the immortal egg (xiandan) or the golden elixir (jindan). Jing is the egg-yolk, the physical body with no intent in it. Qi is the egg-white, on the outside of the body, touching it and surrounding it, always lively with no memory. Shen is the egg-shell radiating out in all directions, where it returns to emptiness (xu). By definition, breathing in internal martial arts is mind-breathing, imagination breathing, or Shen-breathing. The Shen/spatial-imagination expands or lifts causing the whole body to breath like a puppet controlled from the outside. This is our “original” state—oneness with the chaos and order of the cosmos.
Every man, woman, and child who walks into my class is already an apex predator, they do not need power. I just help them figure out how to slip the leash--so they can become stronger, smarter, richer, funnier, and better looking.