The Immortal Physique is a physique classified as a Saint Physique which means that it is able to contend against Saint Heavenly Sovereigns with its might alone.
The Immortal Physique is obtained by using vast amounts of Immortal Origin to destroy and then reform the body of the user. The Immortal Physique is also required for a person to be able to fuse and use the Primordial Immortal Body.
Once someone has obtained the Immortal Physique, their body would be immortal, forever preserved even after the person has died, as it is with the Immortal Emperor, who even after 49,000 years, his body has been preserved in a perfect state.[1][2]