Cadence 原意指一个单位时间完成的周期数，在音乐上，自行车等，依然是这个定义。
按理说，人走路的一个周期，是左右脚完成各一次。马有四只脚，哒哒哒哒，一个Cadence.
但是，习惯上，人们把一步定义为一只脚跨一次，那么大多数人以为一个Cadence就是一步。
但很多搞基础的，还是认为一个Cadence是一个周期，两步。
所以，如果你有时看到长跑最佳Cadence是90，不要奇怪。
维基百科的英文版，还是这么定义的。但中文版似乎是一步算一个周期。
https://en.wikipedia.org/wiki/Cadence_(gait)
Cadence in sports involving running is a measure of speed calculated as the total number of full cycles (of both a right and left foot strike) taken within a given period of time, often expressed in steps per minute or cycles per minute. It is used as a measure of athletic performance.
It is similar to cadence in cycling. In running and racewalking, increasing cadence can be beneficial.[1]
In sports such as weightlifting or bodybuilding, cadence can refer to the speed or time taken to complete a single lift, rather than how many repetitions of a lift are completed.
https://zh.wikipedia.org/zh-cn/%E6%AD%A5%E9%A2%91
步频指的是单位时间内走动的步数。
