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CTS Field Test: Why Two 8-Minute Efforts Instead Of One 20-Minute Effort?

(Excerpted from “The Time-Crunched Cyclist, 2nd Ed.” by Chris Carmichael)

You can find the CTS Field Test instructions and training zones calculator here.

There are numerous methods for field testing, involving efforts of varying durations. The CTS Field Test consists of two 8-minute, all-out time trials separated by 10 minutes of easy spinning recovery. If you have read my previous books, you’ll notice this is different from the original recommendation of two 3-mile time trials. The difference is mostly one of semantics: Instead of gauging improvement by completing 3 miles faster, I have changed the test so you can gauge improvement by covering more distance in 8 minutes. This updated recommendation also translates better to indoor trainers, where distance isn’t typically measured at all. It also reflects the increased use of power meters, because training with power relies heavily on information about your sustainable output for a given period of time rather than on distance.

In a study published in the Journal of Strength and Conditioning Research (Klika et al., 2007), the CTS Field Test was shown to be an effective method for establishing training intensities. Fifty-six participants performed both a lactate threshold test in a lab and the CTS Field Test on an indoor trainer before a CTS-designed, 8-week, power-based indoor training program. At the end of 8 weeks, participants performed both tests again and, on average, experienced a 12.9 percent increase in power at lactate threshold. There was a statistically significant correlation between their improvement in the lab and their improvement as measured by the CTS Field Test. The study concluded that the CTS Field Test is “a valid measure of fitness and changes in fitness, and provided data for the establishment of training ranges.”

Why An 8 Minute Effort For The Field Test?

Some athletes and coaches ask me about the rationale behind the two 8-minute efforts that make up the CTS Field Test. My field test is unique in its brevity; it’s not a 60-minute or even a 20-minute time trial because I’ve found that I don’t need to put athletes through such an effort to gather the necessary data. It’s not that a 60- or 20-minute time trial effort won’t work; in fact, those tests work quite well. However, my coaches and I work with a very broad spectrum of athletes, and a field test of two 8-minute efforts can be performed well by novices as well as experienced masters competitors and even pros.

I prefer two 8-minute efforts over one longer effort because I believe there’s valuable information to be gained from observing your ability to recover from and repeat a hard effort. With a 10-minute recovery period between efforts, an athlete with a well-developed aerobic engine will be able to complete the second effort with an average power output within 5 percent of the first effort. If your average power from your second effort is more than 10 percent lower than your first effort, that doesn’t change your training prescription, but it gives you one more marker by which you can evaluate progress the next time you complete the test. For example, as the average power outputs for your two field test efforts become more equal, that is a sign that your training has improved your ability to buffer lactic acid and process lactate. The first effort took less out of you, and you were able to recover from the effort more quickly, leading to the ability to perform a second effort at an equal power output after just 10 minutes of easy spinning recovery.

Sometimes an athlete has a higher average power on the second effort of the CTS Field Test, and this can often be attributed to one of two factors: You were cautious on the first effort and held back, or you didn’t warm up well enough before the field test (the first effort, then, was, in essence, the end of your warm-up). In either case, your training ranges are established from the higher of your two average power outputs or heart rates, so the fact that the CTS Field Test consists of two efforts allows you to establish accurate training ranges despite performing poorly on one part of the test. In a test that consists of one longer effort, either the learning curve of the test or a poor warm-up is more likely to result in training intensities that are lower than they should be. In the long run, this isn’t all that harmful to an athlete’s training, because training intensities will most likely be corrected by subsequent tests, and most athletes make performance gains even if their training intensities are a little lower than they could be. Nevertheless, through testing thousands of athletes with the CTS Field Test, I have found that it provides greater accuracy the first time around as well as in subsequent tests.

The CTS Field Test Versus Other Performance Tests

The other major question my coaches and I are asked about field testing is whether the power or heart rate we use to establish training ranges is equal to an athlete’s power or heart rate at lactate threshold. The answer is no, but the results from the CTS Field Test correlate predictably with results from laboratory testing, so a conversion factor can be applied to your numbers to establish accurate training ranges.

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One of the reasons some coaches prefer longer field test efforts is that longer tests result in average power numbers that are closer to actual lab-tested lactate threshold power outputs. The reason for this is that you can maintain an effort well above your lactate threshold for a short period of time, but because lactate threshold pretty much defines the upper limit of your sustainable power output, if you ride long enough you’ll settle into a pace that’s very close to—and most likely below—your lactate threshold power output. But this is another situation in which sports science doesn’t necessarily work to an athlete’s benefit. Yes, a 60-minute time trial could provide a relatively accurate estimation of your lactate threshold power output, but only if you can stay motivated to ride all-out for a full hour. If you can’t—and there’s no shame in that; most novices and amateur racers struggle with such a long, intense effort—your numbers are going to be low, and you’ll establish training intensities that are lower than they should be. And even if you could stay motivated enough to complete a great 60-minute time trial, it would be difficult to integrate that into your training program on a regular basis because it’s such a demanding workout in and of itself.

After thousands of tests, my coaches and I have found that the CTS Field Test generates average power outputs that are about 10 percent above an athlete’s lab-tested lactate threshold power output. In the calculations that I present for establishing your own training intensity ranges, this 10 percent is already factored into the equations in the tables. In other words, you’ll take your actual power output or heart rate from the field test and plug it directly into the equation. We have been using the CTS Field Test and the corresponding training intensity calculations for many years, and the accuracy of this method was proven in the Klika et al. study (2007), which was conducted in Aspen, Colorado. The study found that participants’ maximum sustainable power outputs, as measured by the CTS Field Test on an indoor trainer, were 7.5 percent higher than their lab-tested power at lactate threshold. However, it is important to remember that the study was conducted at an elevation of 9,000 feet, where not only is power at lactate threshold lower than at sea level, but the ability to sustain efforts above threshold is even more limited. Therefore, I have continued to use the 10 percent conversion factor for calculating training intensity ranges from CTS Field Test data.

One popular field test, published in Training and Racing with a Power Meter by Hunter Allen and Andrew Coggan, is a 20-minute time trial. This test is a good one; it’s short enough that many athletes can complete a high-quality effort. Allen and Coggan also use a conversion factor to account for the difference between an athlete’s field test power and his or her predicted lactate threshold power. In their system, athletes record their average power output from a 20-minute time trial, multiply this number by 0.95, and then apply a series of percentages to the resulting power output to establish power training intensities. They multiply by 0.95 initially because an athlete’s 20-minute power output will be about 5 percent higher than that same athlete’s power output in a 60-minute effort—which is also about equal to an athlete’s lab-tested lactate threshold power output. Essentially, if you consider a 60-minute test to be roughly equal to power at lactate threshold, then a 20-minute test will give you a power output 5 percent higher than that, and the CTS Field Test will give you a power output another 5 percent above that.

Before conducting the CTS Field Test and calculating training intensity calculations based on it, I want to point out that it is important not to get too caught up in performance testing. It’s a valuable component of training, but some athletes train for the tests the same way some schools teach to standardized exams. Your performance as a cyclist goes beyond your ability to produce more wattage in a performance test, and regardless of improvements in your power at threshold, you’ll still get dropped from the local group ride or finish at the back of the pack in a criterium if you fail to learn how to apply your strength in real-world cycling situations. Races are not won in the lab or on the indoor trainer, and I’ve yet to meet a cyclist who describes his or her best day on the bike by talking about a performance test. Do the testing, use the results to enhance your training, but always remember that your identity as a cyclist is much more than a collection of testing data.

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Comments 24

  1. Pingback: Three Options for the Functional Threshold Tests No One Likes - Simple Endurance Coaching

  2. Do you just get the 2 averages for the 2x 8mins, add them together and divide by two to get your ‘ftp’ number?

    1. No! Use the highest average between the two tests! If on the first you did 200w avg. and on the second 198w avg., use 200w for your calculation. The same goes to heart rate. 🙂

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  4. I’m using HR zones (no power meter) and when I get my avg for the 8 min x 2 field test do I need to adjust by multiplying by .9 or .95?
    My avg last time I took it was 170 for both 8 min intervals. I from what I read in the latest Time Crunched book I was thinking I should just use 170 to calculate my training zones. But, after a couple of week it felt too high and so I multiplied by .95 and have been using that. –maybe I just answered my own question? 😉 My recent 20 min. field test was significantly lower at 162 avg after training consistently for 23 weeks—-and multiplying that by .95 but that might be too low?

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  8. My 8min TT power is 292W, my 20 min TT is 264W and my measured MLSS (30mins @ constant power is 235W). All done on the same m/c (Wattbike).
    That makes my 20min power 112% of my LT2 or MLSS and my 8min power 111% & 124% of my 20min and MLSS power respectively. Thats quite a big difference compared to 10%. Do you know what the 90% confidence interval is of your data (i.e. your data gives 10% higher than LT for 8min power) and also what threshold protocol are you using (DMAX, 1mmol above baseline or 60min average power)?

    1. 1. He tested thousands of athletes. which makes your personal results relatively insignificant. (<0,001%)

      2. your physique is probably more neuromuscular based? (im guessing youre not a skinny climber) which could explain why your shorter efforts are stronger in comparison. (assuming the 0,9 factor is relatively accurate) ex. a track rider would probably have insane 1-5 min or maybe even 10min power, but might have, in relation, terrible 30min power. typically, the decrease in power for track riders are quite significant over a longer time period.

      3. mentally, it is much harder to ride against 'discomfort'. is it possible that even in the lab, that longer efforts were not actually(max efforts)? I know that's the case for me.

      4. im pretty sure this test is not designed and does not intend to identify(although it could) an exact FTP but to help establish effective training ranges. key word being "range". despite the possibility of result-inaccuracy , the probabilities of the determined values lying within the 'correct' spectrum should be extremely high if not spot on. In the end of the day, we probably vary more on a day to day bases just by a bad night sleep or too much/little food, or fatigue from daily work etc.

      5. after all, the 8min test is just an abbreviated/ ''easier'', more "comfortable" way to get similar data. if you are one of the lucky ones who have the chance to be lab tested, or are able to bang out a great 60min or 20 min effort, I would suggest to do that over this of course. there is more data to back the accuracy, if it give you a better peace of mind.

      lastly, if you are not convinced of the methode, don't use it. or if its just for curiosity, id suggest reading the papers and articles that support his findings. ex. '…accuracy of this method was proven in the Klika et al. study (2007)…' maybe you'll find some answers there. personally, after looking at a few power profiles(fit ones in my opinion, Kat 1 or above racers) on strava, and my own data from the past years, the 0,9 factor came quite close to be Frank, it varied a bit of course. maybe +- 2-3%. so I am quite convinced. in the end, its just to have a range to train within and to have an 'anchor point'. 🙂

    2. I had a very similar experience where it appears the power range over estimates my FTP. This is my first time following a structured training plan. Prior to this I spent most of my time on a track bike. In the TCTP, SteadyState is just below lactate threshold. It defines heart rate range as 92-94% of highest CTS field test average and the power range as 86-90% of highest CTS field test average. For me 10% off the highest field test average is not a sustainable amount of power for an hour long duration. However the heart rate range is spot on. It’s just below what other tests believes is my lactate threshold. Also interestingly enough when I ride in the SteadyState heart rate range my average power output is equal to the estimated FTP results I have got from other tests. In short, I think this is a good test for measuring progress and for me a good test for creating heart rate intervals. I think if you are really after figuring out your FTP I’d conduct a different test if you believe the results of this one are unsustainable for an hour.

    3. Using the 10% conversion also over estimated my FTP using the results of a 20 min test conducted around the same time. I wouldn’t use the 8 min test to get ftp (more like 15%). I only use it to get training zone ranges for the time crunched cyclist plan.

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  11. Is the 8-minute test method an estimate of an athlete’s power at VO2Max?

    If so, given lactate threshold can occur at wide range of %VO2max, even in trained individuals, wouldn’t the 0.9 conversion factor give inaccurate lactate threshold estimates for many athletes?

    Or is 0.9 factor simply an empirically observed relationship between the 8 minute and 60 minute power of the athletes you have studied?

    1. Totally agree – the 90% confidence interval of the data will give out more info. My 8min power is 124% of my LT or in my case MLSS. Normally though 5min power is used to equate to vo2max power or vVO2max during an incremental test. I suppose it depends on my anaerobic capacity and buffer capacity and also how driven you are.

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  14. Are there main differences between CTS zones and Friel (for Cycling) zones? I started using Training Peaks and I don`t know what the best way to setup my training zones.

    I mainly use CTS workouts.

    Thanks in advance.

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