Ayurveda distinguish three doshas : Vata (the movement, elements ether and air), Pitta (the processing, elements fire and water) and Kapha (the material, elements water and earth).
These doshas correspond with physical and psychic attributes.
Many tests can reveal you your ayurvedic constitution. You can be monodoshic (a dosha is prevailing) bidoshic (two doshas preavailing equally) or tridoschic (all doshas equally represented, so you are surely never sick and massage is useless).
If the asseur know your ayurvedic constitution, he is able to personalize the massage.