sampidya payum parsnibhyam
vayum utsarayañ chanaih
nabhyam kosthesv avasthapya
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
When Maharaja Prthu practiced a particular yogic sitting posture, he blocked the door of his anus with his ankles, pressed his right and left calves and gradually raised his life air upward, passing it on to the circle of his navel, up to his heart and throat, and finally pushed it upward to the central position between his two eyebrows.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The sitting posture described herein is called muktasana. In the yoga process, after following the strict regulative principles controlling sleeping, eating and mating, one is allowed to practice the different sitting postures. The ultimate aim of yoga is to enable one to give up this body according to his own free will. One who has attained the ultimate summit of yoga practice can live in the body as long as he likes or, as long as he is not completely perfect, leave the body to go anywhere within or outside the universe. Some yogis leave their bodies to go to the higher planetary systems and enjoy the material facilities therein. However, intelligent yogis do not wish to waste their time within this material world at all; they do not care for the material facilities in higher planetary systems, but are interested in going directly to the spiritual sky, back home, back to Godhead.
From the description in this verse, it appears that Maharaja Prthu had no desire to promote himself to the higher planetary systems. He wanted to return home immediately, back to Godhead. Although Maharaja Prthu stopped all practice of mystic yoga after realizing Krsna consciousness, he took advantage of his previous practice and immediately placed himself on the brahma-bhuta platform in order to accelerate his return to Godhead. The aim of this particular system of asana, known as the sitting posture for liberation, or muktasana, is to attain success in kundalini-cakra and gradually raise the life from the muladhara-cakra to the svadhisthana-cakra, then to the manipura-cakra, the anahata-cakra, the visuddha-cakra, and finally to the ajña-cakra. When the yogi reaches the ajña-cakra, between the two eyebrows, he is able to penetrate the brahma-randhra, or the hole in his skull, and go to any planet he desires, up to the spiritual kingdom of Vaikuntha, or Krsnaloka. The conclusion is that one has to come to the brahma-bhuta stage for going back to Godhead. However, those who are in Krsna consciousness, or who are practicing bhakti-yoga (sravanam kirtanam visnoh smaranam pada-sevanam), can return to Godhead without even practicing the muktasana process. The purpose of muktasana practice is to come to the brahma-bhuta stage, for without being on the brahma-bhuta stage, one cannot be promoted to the spiritual sky. As stated in Bhagavad-gita (14.26):
mam ca yo ’vyabhicarena
sa gunan samatityaitan
The bhakti-yogi, practicing bhakti-yoga, is always situated on the brahma-bhuta stage (brahma-bhuyaya kalpate). If a devotee is able to continue on the brahma-bhuta platform, he enters the spiritual sky automatically after death and returns to Godhead. Consequently a devotee need not feel sorry for not having practiced the kundalini-cakra, or not penetrating the six cakras one after another. As far as Maharaja Prthu was concerned, he had already practiced this process, and since he did not want to wait for the time when his death would occur naturally, he took advantage of the sat-cakra penetration process and thus gave up the body according to his own free will and immediately entered the spiritual sky.