Most fitness trackers calculate your “training load.” Here’s what it can and can’t tell you.
You just finished a long, hard bike ride. But how hard was it, exactly? That depends on what you measure: How far did you ride, and how fast? How hilly was the route, and what heart rate zones were you in?
In the 1970s, exercise physiologists came up with the concept of training load, which they believed could offer a fuller picture of the difficulty of a workout. Training load combines the intensity and duration of a workout into one number that’s meant to estimate the stress of a bout of exercise on the body. By understanding how different kinds of workouts compare in terms of difficulty, the thinking went, athletes could better structure their training routines with the right mix of easy and hard days.
“It’s a brilliant concept,” said Carl Foster, a professor emeritus of exercise and sports science at the University of Wisconsin La-Crosse. For many competitive athletes, the idea is intuitive, he said. It can also be useful for the occasional exerciser who wants to get fitter.
Today, many fitness trackers and GPS watches, including those from Garmin and Coros and the most recent version of the Apple Watch, use algorithms to approximate training load and present that data alongside other stats like step count and heart rate.
While some fitness experts consider training load a useful way to gauge the effectiveness of an exercise routine, others warn that paying too much attention to a complex metric generated by an algorithm might distract you from listening to your body.
Here’s how to interpret your training load data with a critical eye.
What does training load mean?
Put simply, training load combines the length and intensity of a workout into one metric.