Joe Friel reposted an article earlier this year on Efficiency Factor in running. Efficiency Factor (EF) can be viewed in Training Peaks software and he describes how it is calculated. This post describes how I went about calculating EF in R using a single gpx file. What is Efficiency Factor (EF)? Essentially, EF is the average distance that you are propelled forward per heart beat. The higher the number, the more efficient you are at running.