Running economy (RE) is typically expressed as the volume of oxygen consumed per kilogram of body weight per kilometre of running at a given speed. A runner with good running economy consumes less oxygen at any given pace than a runner with poor economy.
Two runners with identical VO2 max can perform very differently if their running economy differs. Elite African runners — particularly Kenyan and Ethiopian athletes — often have comparable VO2 max values to their European competitors but substantially better running economy, which contributes to their performance advantage.
Running economy is influenced by: biomechanics (stride mechanics, contact time, vertical oscillation), muscle fibre type (more slow-twitch fibres correlate with better economy), tendon stiffness (efficient energy storage and return), training volume and history, and body composition.
Running economy is trainable. High training volumes, plyometric training, and strength training have all been shown to improve economy in studies. Even experienced runners can improve economy over months of consistent training.
In the VDOT framework, running economy is implicitly captured: a runner with high economy will produce a VDOT that exceeds their laboratory VO2 max (because they race faster than their oxygen consumption alone would predict). This is why two runners with the same VDOT may have different VO2 max values.