HRM-Run has an accelerometer in the module that measures torso movement to calculate 3 running metrics:

• Cadence - The number of steps per minute. It displays the total steps (right and left combined)
• Vertical oscillation - The bounce in your running motion. It displays the vertical motion of your torso (measured in centimeters)
• Ground contact time - The amount of time in each step that your foot spends on the ground while running (measured in milliseconds)