Variability Index (VI) is a metric that shows how steady your power output was during a workout. It helps you understand whether you maintained a consistent effort or if your intensity fluctuated, allowing you to better analyze your pacing and performance.
Variability Index compares your Weighted Average Power to your Average Power to measure the smoothness of your effort. A score close to 1.0 indicates a very steady and consistent effort, while a higher score reflects a more variable, punchy workout with frequent changes in power.
VI is categorized to help you quickly interpret your performance:
Tracking your VI helps you assess whether your pacing execution matched the goal of your workout. For example, a low VI is ideal for endurance rides or tempo runs where a consistent effort is key. Conversely, a high VI is expected and desired for workouts involving intervals, hill repeats, or races with frequent pace changes.
Neither a high nor low VI is inherently better; it depends entirely on your session's objective. By tracking VI over time, you can see if your ability to pace consistently on endurance efforts is improving or if you are hitting the intended variability in high-intensity sessions. It also provides important context for other metrics like Decoupling, which is most reliable in sessions with a low VI.
VI is calculated by dividing your Weighted Average Power by your Average Power for a session.
Weighted Average Power is a smarter version of average power that gives more weight to harder efforts. This provides a more accurate representation of the true physiological cost of a session, especially when your output wasn't perfectly steady. Because VI accounts for these fluctuations, it offers a more nuanced view of your pacing consistency than average power alone.
Variability Index (VI) measures the consistency of your power output, indicating how smooth or variable your effort was during a session. By comparing your Weighted Average Power to your Average Power, VI helps you analyze your pacing and assess whether your performance aligned with your workout's goals, such as maintaining a steady pace for endurance or executing sharp intervals.