
W Prime is a great way to measure your training load.
Not everyone owns a power meter for their bike. Some people do not want to make the investment in equipment. Some just want a great workout and want to see how hard they can push their bodies. W Prime in PerfPro Studio is a great tool to help athletes measure their effort better.
PerfPro Studio has added features almost weekly now for several years. This is a robust, solid training platform that is my go-to for indoor studios. It is consistent and is easy to operate. PerfPro Studio shows riders what they need to know, both on a dashboard and graphically, so they can achieve their goals.
Since 2015, I have been employing W Prime testing at my studio, Cycling Center Dallas. The clients perform roughly two days of testing every 9 weeks. Then we try to get their best efforts for:
- 13 minutes,
- 8 minutes,
- 5 minutes,
- 3 minutes, and sometimes
- just 1 minute.
The result looks a bit like this:

At times, I’ll use one data point and drop another, because cyclists can’t be strong at every effort. They’re human. I dropped the 13 minute effort from this client, and we achieved a Critical Power Signature of the following:
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149 watts for Critical Power – Below this number, they’re cycling AEROBICALLY. Above this number, they’re cycling ANAEROBICALLY. A rougher translation might be “You can cycle aerobically for a long time. You can cycle anaerobically for just a short time.”
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The next important point for the cyclist is a value known as “W Prime” or W’. This is your ‘ANAEROBIC’ Work Capacity, or (AWC). Using these hard efforts helps me get this W Prime number. Think of this number as your “Anaerobic Bank Account”. When you pedal ABOVE Critical Power, your W Prime will begin to decline. You’re borrowing from the bank, and while it always replenishes, it can take time.
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EVERY cyclist has a unique Critical Power, and EVERY cyclist has a unique AWC, or W’. Just like every automobile out on the road has a different sized fuel tank, all you need to look at, as the driver, is whether the tank is at full, empty, or somewhere in between.
For this client, her Critical Power was initially calculated as 149 watts, and her AWC was calculated at 5689 Joules of work. This is a modest number for a recreational cyclist, who has ambitions to improve and race triathlons. The goal for us was two-fold;
- RAISE the Critical Power, and,
- INCREASE the W’.
This time, however, we used a new protocol for intervals, which I’ll describe below.
Remember what was mentioned before? When a cyclist rides ABOVE Critical Power, she DEPLETES her W’. When a cyclist rides BELOW Critical Power, it returns to full, over time. It’s my belief that we can now SEE a “Training Dose” by performing intervals of an intensity that will DEPLETE W’ down to a certain level. We then RAISE, LOWER, or MAINTAIN it, with more or less power over time. When a cyclist’s W’ is back up to, say, 80%, they can perform a higher quality or duration interval above Critical Power. When a cyclist’s W’ is down at 20%, they probably don’t have that much more to give. They can quickly become exhausted, and need to recover for an extended period of time.
Viewing W Prime in Real Time.
The intervals this month looked very much like this:

Do you see that Green line? THAT, is W Prime!!!
We used our time in the studio to deplete W’ down to between 20 and 30 percent. Then we had cyclists increase or decrease their efforts between recoveries, to try and stay in that range. We did this for 8 weeks. The cyclists learned how their bodies can interpret W prime, better understand what it means, and how to employ it. Then, just this week, we tested, and the protocol went like this….
PerfPro and W Prime can help you measure your effort.
When the cyclists began their intervals, the goal was NOT to try and “Break a record.” Instead the goal was to “Ride to deplete W Prime at a rate that left them either just above zero, at zero, or slightly below zero, when the interval ended.” IDEALLY, the cyclist would be able to ride at an intensity that left W Prime BELOW ZERO with several seconds, maybe even closer to a minute, remaining, and they could then “Break Through” on their effort, achieving a higher average power than previous efforts, and “Resetting” the Critical Power and AWC calculations when the effort was over.
Here is a PERFECT example of just how well one of these cyclists achieved that goal. She truly did “Leave With Nothing Left!”

Watch the GREEN LINE (W Prime), as the BLUE LINE (WATTS) gently rises above the WHITE LINE (Critical Power).
Just for the sake of knowledge, the RED LINE shows Heart Rate, and the PURPLE line is a MOVING AVERAGE of power; it mimics the physiological response to effort.
It was fascinating to watch the client as she worked through this 8 minute effort. She went from determined, to uncomfortable, and her breathing became more and more labored as she pushed for her breakthrough. You can actually see that with about a minute left, she shifted, and stood for her final effort. The Blue watts line dipped and the green W’ line hit a short plateau. Finally, she was back on, pedaling a harder gear, at a higher cadence, and straining her body to PUSH until she reached the end, COMPLETELY SPENT and GASPING!
Watching W Prime to gauge effort can be a FAR superior way to achieve a fitness breakthrough. The green line and W’ on the dashboard show you just how much you have left, and if it ends up going BELOW ZERO, you just go into PerfPro Analyzer and run another Critical Power Calculation, and get a new value. For this client, with this one interval, she raised her Critical Power from 149 watts to 155, a 4% boost! That’s more AEROBIC power, less need to exploit ANAEROBIC power, and more efficiency at speed.
PerfPro Studio is one of the most complete Software Training packages available, and it is the perfect complement to your indoor ergometer. If you have questions about Training, PerfPro, or how to get the most out of your indoor setup, contact us and we’ll arrange a videoconference

