Why does power ‘jump around’?
It’s to do with how your body produces energy and how often your power meter calculates the energy you’re producing.
Your body doesn’t produce energy in a smooth and uninterrupted way. Rather, it’s ‘stochastic’, a word which describes things happening unpredictably that, over time, appear to generate a pattern. But your power meter is producing a calculation every second. Matching the two means that your power meter reading will sometimes produce much lower (or higher) numbers than the overall pattern might suggest.
Which means that real-time (every second) power numbers can be very ‘spiky’, sometimes high, sometimes low, sometimes somewhere in the middle.
You can run using real-time power numbers. But they can be a little difficult to follow. And they can lead your watch to believe you’re not running to your power targets.
The alternative is to use power averages. And there are a few different types:
- Smoothed power
- Workout average
- Lap average and Last Lap average
- Step average and Last Step average
Smoothed power
Smoothed power averages real-time power over a short duration: The Stryd footpod offers 3-second (3s) smoothing; Garmin watches offer 10s smoothing; other apps offer other durations.
Smoothed power is a useful alternative to real-time power, as it removes a lot of the ‘spikyness’, while still offering a power number that (at least for the 3s version) responds quickly to changes in effort and can be used even for short, high-intensity intervals.
Workout average
All power meters offer power averaged over an entire workout. I find it the least useful average, but it can be used for easy or long runs when the target power is for the whole workout.
Lap average and Last Lap average
Power averaged over a lap is most often used for interval workouts, where the workout has a series of steps which your watch implements as individual laps. Lap average takes note of manual laps (pressing the lap button) and auto-Laps (laps at regular distances).
Lap power is useful for interval workouts as the work intervals and recovery intervals will probably have different power targets – average or workout power isn’t useful in this case.
Last Lap average is the average power of the previous lap. Why show this on your watch? Because it gives you an opportunity to review the power for your most recent work interval while you’re recovering from it.
Step average & Last Step average
Power averaged over a specific step in a structured workout can also be used for workouts. The difference between Step average and Lap average is that Step average ignores manual laps (pressing the lap button) and auto-laps (laps at regular distances), which can be useful if you always run with auto-lap enabled.
Which averages should you use?
It’s up to you. My preference is to use lap average and 3s smoothed power values.
Lap average matches the way I structure my workouts (with power targets for each work interval, or for each auto-lapped segment of an easy or longer run). 3s smoothed power is a good compromise between real-time power (too spiky) and smoothing over longer durations (slower response to changes in effort).
When running, I aim to keep my lap average power within the target range. If the lap average is too low, I increase my effort until my 3s smoothed power is higher than lap power, to increase the lap average. If the lap average is too high, I decrease my effort until my 3s smoothed power is lower than lap power, to lower the lap average.
This also builds my feel for my effort, allowing me to establish an effort level that’s within target, then run by feel with occasional glances at my watch if I feel my effort is drifting higher or lower.
👉 Real-time power can be ‘spiky’, but a combination of smoothed power and lap average power should meet most runners’ needs.