Is there a minhag to recite a special Mi Sheberach for the ones that fast? If someone answers Amen to the Mi Sheberah does he become obliged to fast?
A. Traditionally, on the Shabbat preceding these fasts, a special Mi Sheberach is recited for those who intend to fast.
Most communities recite this Mi Sheberach before returning the Sefer Torah to the Aron Hakodesh , but some (generally Western European communities) add it as an additional line to the Mi Sheberach recited for the community (recited after Yokum Purkan).
One who responds "Amen" to this blessing does not need to accept the fast upon oneself.
Rabbi A. Bartfeld as revised by, Horav Yaakov Hirschman, Horav Dovid Pam, Horav Aharon Miller, Horav Chanoch Ehrentreu and Horav Kalman Ochs Shlit’a