When the app plays music, the tempo of the music beat will follow the running pace, so that every step you take will be on the beat of the music. At the same time, it can also record the stride frequency of the last 50 seconds and 50 minutes, and display it for you with a line graph. When paired with an Apple Watch, the Apple Watch can provide cadence data to the iPhone. Refer to the upper limit of heart rate for moderate-intensity aerobic exercise: https://www.cdc.gov/physicalactivity/basics/measuring/heartrate.htm
