Yoga, is used in sanskrit language, which in English language translates into sum, which in this aspect means, various organs/energies working in tandem with each other to reach a common goal, which is, the physical body, the psychological body and the biological body combine together, to reach health and well being. Yoga has many forms, physical exercises by which the joints are twisted for flexibility (which indirectly increases/optimises the flow of blood in organs) due to this twisting the psychological virtue of the body disintegrates itself from thoughts and memories, in addition to increasing blood in the organs and taking away the brain from thoughts twisting also changes the course of the breath, making it heavier hence positively affecting the chakras within.
The other aspect of yoga is Dhyan (referred to as meditation commonly), in which the psychological virtue of the body takes the driver seat and regulates the blood flow, disintegrates the conscious mind from the thoughts and observes and heals the chakras.
Depending upon the analysis (done by the master) which is energy is dominant within the person, any of the yoga classifications are suggested, as when the root chakra is dominant the person takes its first introduction into yoga by adopting physical yoga and then post regulating that energy the meditative part is suggested to be undertaken.
What so ever variant of yoga may you adept, the ethos remains the same, which is of wellbeing, it starts with physical well being and then trickles down to spiritual knowledge. Vedas have illustrated various postures and their significances, the sages who undertook the path of improving and improvising thyself developed methodologies, postures of the body, fingers, legs, feet and varying head positioning, hence aiding in improvising the energy centres within and also altering the circumventing ones.