Sashtang Namaskar in the Hindu religion denotes the most humble way of letting go of one’s self [ego or identity] at the feet of God. It also means submission of all [symbolized by the Eight Limbs] at the feet of God. This all includes the Mind, which is symbolized by the touching of the Head to the ground.
Sashtang Namaskar thus is the complete surrender of the Mind and Body at the feet at of God and is the most devotional form of Salutation or Prayer.
Some Hindu religious scholars recommend that a certain number of Sashtang Namaskars for some Hindu deities.
Sun [Surya Dev] – Seven
Vishnu or any of his Dashavatars-Five
However, in my opinion, a Namaskar, being a most humble devotional submission to God, those unable to perform Sashtang Namaskar can bow their heads or fold their hands before God. It is the feeling and emotion with which the action is performed, which is as important as the physical act.