[Avodah] standing for mitzvot

[Eli Turkel]

"The Avudraham (in his siddur, weekday Shacharit) writes that there are
six mitzvot which must be performed while standing, and their initials
spell "alotz shalem": [the cutting of the] omer, [kiddush] levana,
tzitzit, shofar, lulav, and mila."

I thought tekiot demeushav were called that because one was not
required to stand and it is only a minhag to stand for them.

Does one have to standind for counting the days of the Omer?

-- 
Eli Turkel