how to measure CTL

daveryanwyoming

If you collect second by second power data(or data sampled much faster than 30 seconds) then you could calculate NP accurately. If you ride fairly steady efforts on your trainer you can get a very good estimate by skipping the 30 second averaging. It's what I do when I ride gym ergs. I block my workouts into 2.5 or 5 minute chunks and ride a steady power for at least that long before bumping it up or down. So a workout might look like:

min. pwr
2.5 150
2.5 190
30 245
2.5 190
2.5 150

That's typical for a short low SST day on the gym erg I use with the power steps it gives.

To calculate NP, just take the pwr column and raise it to the fourth power (pwr^4), multiply each raised power term by its time in minutes. Add them all up and divide the total by total time in minutes and take the result to the fourth root (average^0.25). That's a very good estimate of NP for relatively smooth data.

If you ride fairly steady intervals even with steady ramps in power the AP and NP for the intervals are often the same or very close. But the AP and NP for the overall workout including warmup and cooldown and rests between intervals is usually quite a bit lower. If you get tricky with things like microintervals they'll be quite a bit different.

-Dave