In the physical manner the person performs the austerity, but does not have the inner desires to change his or her life and therefore, it is just a physical act. While in the psychic austerity the person controls his or her inner desires along with performing a physical act. Unless the austerities are performed in psychic manner, they do not produce the much needed results. After all, the whole purpose of austerities is not just to simply make the body suffer, but to change our desires. Once that happens the person will be on the path to spiritual uplift.
Austerity is part of right conduct.
One day of total fasting is called upavas. Fasting completely until death is done when life is close to an end. Such fasting is considered very auspicious and is called Physical Anasan. Bhav Anasan refers to the total control of our inner desires for a short or a long time. If this austerity is cultivated then only we will be able to strive for spiritual uplift.