Is "posture" a countable noun?

Hi, there
Is "posture" a countable noun? We know "gesture" is countable, then what about " posture"?
There is a sentence in one textbook as quoted below:
"...they also express their feelings using unspoken' language' through physical distance, actions or posture." It seems quite weird that posture is uncountable here, but I often come across the expressions like" a sitting posture". So, is it because of the error of the textbook or some other reasons?

Thank you in advance!
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