Determing threshold power with a field test is the most important first step to a power-based training program

A simple 20-minute field test can determine your power at threshold and is the best starting point for a power-based training plan. Knowing one’s threshold wattage gives you the ability to use wattage-based training zones and to understand power readout in real time on the bike. Most importantly, you will be able to analyze training data on your computer and measure your cycling improvement.


A field test is a real world and scientifically supported method for cyclists to determine their threshold power. It is performed by the cyclist going as hard as they can for 20 minutes, just like a time trial. The average wattage from the test is used to determine the rider’s power at threshold.


Threshold power is the wattage-based equivalent of the Federal Reserve’s interest rate. It is the goto number for a sport science and power based training program because it 1) measures your fitness and 2) establishes your wattage-based training zones.

To perform a 20-minute wattage based field test, here’s what you will need:

  • an accurately calibrated, working, reliable power meter capable of downloading the test data
  • a good stretch of road (or a good trainer) w/o interruptions for 20 minutes (climb preferably)
  • a heap of motivation
  • a maximal effort
  • power analysis software
  • the the average power for the 20 minute test

You can download a wattage spreadsheet at, where the user can enter threshold power from the field test and have the sheet calculate their wattage based zones.

Course Selection

Select a section of the road where you can drill it for 20 minutes. Avoid stop signs, intersections or anything that will impede your effort. If you have a steady 3-8 percent grade climb that lasts for 20 minutes, that is my first preference for athletes. I recommend starting from the bottom of the climb and going as fast as you possibly can, full gas, for 20 continuous minutes. For athletes without such a climb, my second choice is a flat stretch of road free of any downhill or tailwind sections.

Great field test courses:

Boulder, CO: Flagstaff Road
Tuscany: the Monte Serra
San Diego: Mt. Palomar
Arizona: Mt. Lemmon
And hundreds of others scattered around the world


Make sure your power meter is calibrated and recording data accurately. If the power meter is new, it’s also a good idea to verify that you can successfully download ride data beforehand. Plan your training block/month/week and choose a day that allows for your best effort. I prefer Saturdays after a Monday-through-Friday rest week. Get pumped up, fueled up and ready to go all out for 20 maximal minutes. Mentally prepare to push your limits for as hard as you can. Warm up like you would for a race and begin the test.

Power-based pacing

Go out hard but not too hard. There are very few of us in the world that should start anywhere near 400 watts! For the first three minutes of the test, use the wattage readout to keep yourself from starting out unrealistically high. Resisting unrealistic wattage will seem counterintuitive at first, but it is the secret to great time trialing and consequently a well executed field test. Ideally you want to start strong and finish strong at the same wattage. This is called a well-paced effort.

Previous data from hard group rides, races, climbs and efforts will also help identify ballpark wattages.

As a coach I try to give a range that I believe the athlete may achieve, but I believe it is even more important to teach the athlete how “feel” the effort and concentrate on going as hard as possible. Expend every ounce of energy during the test. Push through the “spots of bother” and stay with the effort mentally. A well executed field test doubles as outstanding physiological and psychological preparation for time trials and similar duration hill climbs.


OK, fast forward 20 minutes, cool down, finish up your training ride and download your power meter file. The analysis is simple: take the average power from the start to the end of the 20 minute test. This wattage is your 20 minute field test power.

There are more advanced analysis techniques with “normalized power” but that is for another column.

Wattage-based training zones

Now that you know your 20-minute power, you are ready to use percentages of that number to establish your power based training zones. With a simple entry into a spreadsheet like the one available on my site, you can calculate the wattages for your zones 1 – 6.

Twenty-minute power is a physiological snapshot of what an athlete could sustain for 60 minutes or a 40K time trial. This wattage is called “functional threshold power“ and is the gold standard for wattage-based training. Depending on the athlete’s ability, age, strengths and weaknesses, most can sustain 90 – 95 percent of their 20-minute power. .

By referencing these zones during a ride, you’ll know in real time how hard or easy you are riding. Most importantly you can design wattage-based workouts to achieve specific physiological adaptations.

Test again under repeatable conditions

Your first 20-minute field test should not be your last. On your first attempt you’ll learn what it feels like and how that feeling correlates to the 20-minute average power. But the biggest advantage of a wattage-based field test is that athletes can repeat it for comparative data. By testing multiple times across the season and year after year, you can scientifically answer the question with real data: “am I getting faster?” Or “Is my training working?”

When you do test for a second time, try to test on the same roads as before, under the same weather conditions and of course absolutely as hard as you possibly can. February is a great time for a 20-minute field test, and for those athletes who have been working hard, the results can be very encouraging.

Editor’s Note: Frank Overton is the head cycling coach at FasCat Coaching, a cycling coaching company in Boulder, Colorado. His most recent article for was on building a training plan for 2009. For more power-based training tips please visit or Email Frank Overton