In the world of sports performance and fitness, training load is a powerful concept that helps athletes and coaches strike the perfect balance between improving fitness, avoiding overtraining, and reducing injury risk. But what exactly is training load, and how do we measure it effectively? In this article, we’ll dive into the science behind training load, discuss why it’s important to track, and explore the best methods for measuring it—particularly focusing on heart rate and wattage. Finally, we’ll highlight the limitations of using speed to measure external load, especially in outdoor conditions where weather and terrain can skew data.