The semantic role of manner adverbials is to describe the manner in which the action named by the verb is executed. In chronological order, the state portrayed by a manner adverbial starts before or, at least, simultaneously with the action. The state co-exists with the action during its process. Therefore, according to the conceptual structure of the Chinese, it is ordered prior to the verb it modifies.
[1] Loar, J. K. (2011). Chinese syntactic grammar: functional and conceptual principles. New York: Peter Lang.