Abstract
Objectives Some major Chinese medical classics like Huangdineijing (黃帝內經) and Nanjing (難經) assert that a normal person breaths 13,500 times every day. It's just half of real breathing cycles of human. So I tried to find a reasonable explanation to solve this conflict between truth and literal description. Materials and methods To find breath count descriptions in Chinese ancient books, I used Kanseki Repository (http://kanripo.org/). To find precedent research on this topic, I used China National Knowledge Infrastructure (http://cnki.net). Results 33 books refers to human breath cycles for a day, and most of them introduce 13,500 as human breathing frequency of one day. Some recent papers on Laoguanshan (老官山) Western Han dynasty manuscripts show new clues on this topic. Conclusion I assume that 13,500 cycles, the incorrect human breathing frequency of a day, might be originated from adjusting the meaning and usage of the word "Xi (息)".