I am aware of this question asked about zimun, but my question is on mitzvot that require standing up. If one is in a squat position (not fully standing) or leaning over a shtender, is that sufficient for the requirement of standing up? This would apply to standing up for parents, elders, Rabbis, and all other mitzvot I didn't mention that require standing. I ask this because I have seen people who half stand when a Rebbi or Rosh Yeshiva walk by and got me thinking of other mitzvot as well. Please bring sources, thanks.
In the Gemara (Kiddushin 32b), it says that even though one must stand up to his full hight to honor a parent, teacher or an elderly person, however if he forgoes his honor, one is not obligated to do so, but must still do something to indicate a sign of reverence, and Rashi says he can do so by shifting slightly in his seat, and that would be enough.
The same would apply to a Talmid Chacham when honoring the elderly, or for elderly people and Talmidei Chachamim, when honoring one another, (Yoreh De’ah 244:7-8)
when it comes to performing the Mitzvos where one must stand, such as Tzitzis, Tefilin, Sefiras Ha’omer, blowing the Shofar, Netilas Lulav etc. one is forbidden to lean on something, unless he is in a position in which he would be able to remain without the support (Mishnah Berurah 585:1)
When it comes to the Ba’al Koreh, while reading from the Torah, as well as the one called up for the Aliyah, being that he must stand with awe and reverence, it is forbidden even in such a case, unless he is obese, old or sick (Ibid 141:1)
When it comes to the Ba’al Koreh, while reading the Megillah for the congregation, being that the reason why he must stand is only to show respect for the congregation, it is permitted to be leaning on something (Ibid 690:1)
When it comes to Shemoneh Esrei, there is an argument as to whether it is as stringent as a Ba’al Koreh while reading from the Torah, or if it’s like all other Mitzvos (Ibid 94:8)
When it comes to standing while reciting “Vayechulu”, which is considered a “testimony”, see Choshen Mishpat (17:1) regarding the dispute as to whether a witness is permitted to be leaning on something while giving testimony.
When it comes to the Cohen, who must stand while reciting the priestly blessings, being that it is likened to the service in the temple, see Tosafos (Zevachim 19:b) who paskens like the opinion that holds that the Cohen may not lean on anything while performing the service in the temple.