1) During Shemona Esrei we bow four times, #1) at the beginning (Baruch Ata) and #2) at the end (Magen Avraham) of Birchas Avos and #3) at the beginning (Modim) and #4) at the end of Birchas Hoda’ah (HaTov Shimcha).
Though all the bowings are halachically important, the bowing at Modim has an extra significance, as the Gemara says that one who isn’t careful to [properly] bow at Modim, may be punished [after they die] by having their spine turned into a snake after seven years of being buried [and thus possibly forfeit their chance of getting up at Techiyas Hameisim] (See Mishna Berura Siman 121:2)
2) It is forbidden to bow at the beginning and/or end of any other Brachos [even other Brachos that aren’t part of Shemona Esrei, according to the Biur Halacha]. If one wants to bow in the middle of a different Bracha, he/she may do so, but must straighten out for the beginnings and ends of those Brachos. (This is common on Rosh Hashanah and Yom Kippur when many people daven in a bent position)
Halachos for Shabbos Kodesh
1) The proper way to bow is as follows: when saying "Baruch", bend the knees; when saying "Ata", bow forward until all the vertebrae of the spine are totally "bent", (i.e. due to the bowing, they can be seen poking out of the back. However, do not bend so much that the mouth should be parallel to the area of the belt of the pants as that is "Mechezi K’Yuhara- an inappropriate display of ultra religiosity" - Mishna Berura Siman 113:11); when saying "Hashem", straighten yourself back to a fully upright position.
When saying "Modim", bend the head and the body simultaneously, and quickly. When saying "Hashem", first straighten the head, slowly, and then the entire body, also slowly.(The reason for this is so that it shouldn’t seem like a burden to be bowing to Hashem).Some have the Minhag to bend the knees at Modim as well, while other Minhagim do not bend the knees at all by Modim, just the head and the back.
2) If, due to old age, or a medical reason, bowing is difficult, it suffices to simply bend the head a little to display the desire to bow.
Reader’s Question:
One very common situation you didn’t mention [as being prohibited during the recital of Shema] is giving tzedaka while saying Kriyas Shema. My understanding is that it is forbidden during the first parasha but allowed afterwards. Is this correct?
My Answer
True, it is prohibited to give Tzedakah during the first Parsha of Krias Shema. During the 2nd Parsha of Krias Shema the Poskim (based on the Mishna Berura Siman 63:18) say Tzedaka may be given. However, it is still best for gabaim to avoid collecting then. And, as we pointed out a few weeks ago (Click here to see archives, see Halacha for Oct 16 2008), Rav Chaim Kanievsky maintains that though it isnt Asur, you are exempt from giving at that time (Osek b’Mitzvah Patur Min HaMitzvah).
Our holy sages, the Chazal tell us תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן עולם הבא, שנאמר הליכות עולם לו, אל תקרי הליכות אלא הלכות - one who studies [at least two] Halachos daily is assured a portion in Olam Haba - the world to come. (:מגילה כ"ח )