Hi,
Ordinarily a priest is bound to follow the rubrics for the liturgy, which require that the priest genuflect after consecrating the bread and then again after consecrating the wine. Whether or not such a violation would sinful for the priest if he chooses to just bow instead depends on his intention for doing so. Certainly age and illness can prevent priests from genuflecting. Also the Cistercians only bow because this was the practice of the western Church when they were founded in the 11th century. Priests who disregard such rubrics because of a disdain for them from an exaggerated prideful willfulness could be guilty of serious sin.
Fr. Vincent Serpa, O.P.
