Thursday, January 5, 2017

Estimating TSS made easy

My last blog entry described the new way to plan a season with Training Peaks. The Annual Training Plan now offers a choice between traditional duration-based planning and TSS-based planning. When you consider that TSS is Duration x Intensity you can see how it is not so much different as more inclusive.

One major obstacle to using TSS is that it is a number we are unfamiliar with. Supposed you had never ridden in a car or train. The fastest you have every traveled is on a bicycle, one without a speedometer. If I told you my car can go 60 miles per hour you probably would not have any sense of what that was like, even though you know how long a mile and an hour are. You will just have to trust me that after planning and reviewing workouts in terms of TSS for awhile you will develop a feel for it, same as you "know" what 60 m.p.h. feels like.

TSS is Duration x Intensity, with a little scaling to make the results easier to digest. We know what duration is, elapsed time expressed in hours, minutes, seconds, and tenths. To simplify the calculation TSS uses minutes. Where do we find intensity, and how do we express it? Good question. There is no easy answer.

If we are using a power meter we can use something called threshold power, more commonly called Functional Threshold Power (FTP). Lacking power data, if we are using a heart rate monitor we can use threshold heart rate. But what is the threshold? Sports physiologists can debate that question the way football fans can argue over which team has the best offense (an offensive argument if ever there was one!). The simple but very useful answer is the effort that can be sustained continuously for a prolonged period of time. How long? More than fifteen minutes, as long as an hour, maybe even longer under race conditions. This level of activity is set by the body's ability to clear lactic acid; any harder and the lactic acid level in the blood will rise and output will drop. When using heart rate to represent this value we use Lactate Threshold Heart Rate (LTHR). So FTP equals LTHR. More or less.

The beauty of this approach is that it simplifies mapping personal data to functional performance levels. My LTHR is 141. Yours might be 155, but we both feel the same thing at our respective LTHR.My FTP is 169 watts, and yours might be 225 watts. When we map out heart rate and power into zones we ought to feel the same degree of difficulty in the same zone, regardless how many watts our legs are producing or how fast our heart is beating.

Training Peaks offer several ways to divide power output into zones. I happen to use the method labeled "CTS," which I think stands for Carmichael Training Systems. I might switch to a different system, but for now that is the one I have the most experience with. The CTS system uses seven power zones and assigns each a descriptive term. Here are mine:

My FTP:169

Range Start
ZoneDescription(watts)% FTP
5Steady State*179106
6Climbing Repeats204121
7Power Intervals254150

*- Sweet Spot

Intensity Factor is a handy way to express how hard we were working compared to a threshold effort. If we were to ride our bike at FTP for one hour, that workout would get an IF score of 1.00 and a TSS of 100. If we could manage the same effort for two hours -- highly unlikely -- we would still be at IF 1.0 but would get a TSS of 200. Normally we expect to see IF values in the range of .50  to .90. As a rule, the longer the workout the lower the IF.

What is missing from the Training Peaks personal data is percent of FTP. I have a spreadsheet to compute that. You can see the results in the last column. It is simple, just the Range Start value divided by FTP expressed as a percent. This is helpful for what comes next, using the Workout Builder, but it has other uses as well.

Care to learn more about IF and TSS from the guy who created it? Here you go.

Let Workout Builder do the math

Let's assume you want to plan a bike workout with these criteria:

Duration: about 2 hours
TSS: about 120
Main set: Tempo intervals, 5 x 12 minutes with 3 minute recoveries.

In Training Peaks all you have to do is add a new bike workout to your calendar, click on the Workout Builder link (see below, click to enlarge). To build the workout you drag interval icons representing warm-up, work, recovery, and cool-down from the top of the window to the timeline and edit a few details such as duration and intensity. Remember what I said about knowing the %FTP for your power zones? You need that because the Workout Builder uses %FTP to specify intensity. It does display the descriptive text, but not the zone.

In this case I made the work interval intensity 95% of FTP, which puts it mid-way through my Tempo rage of 154 to 178 watts. Remember, that is my Tempo range; yours will be different. Notice that the text does not mention power zone 4. It does say 161 watts, and "Tempo." My Garmin will not display "Tempo" but it will display power (and heart rate) zones down to a tenth of a zone, so I should expect to see something around 4.5.

A thirty minute warm up and a fifteen minute cool down bring the total duration to two hours. Training Peaks estimates the overall intensity factor for this workout at 0.81, another way of saying 81% FTP, and estimates a TSS of 130.9.

There are just two ways to increase the TSS for a given workout. Increase the duration, or increase the intensity. If you are short of your weekly TSS goal you can increase the TSS of a workout, or add another workout. Obviously you must do so cautiously, as you only have so much time and your body can only absorb so much work.

If you had to come up with IF and TSS for every planned workout by hand you would probably give up after one month of planning. The workout builder takes the pain out of the math and makes planning by TSS as easy as planning by duration.


  1. Hey Tim, I'm a little confused. I thought that "sweet spot" training was 88-93% of FTP, as opposed to the 106% you have listed. What am I misunderstanding?

    1. Please don't blame Tim, I'm pretty sure the confusion is mine. I am new to WKO4 and have seen "sweet spot" tossed around without understanding what it really means. Training Peaks labels PZ5 "Steady State" and the range is 106-120% FTP. So I thought Steady State and Sweet Spot were the same, only I also wondered why an effort above FTP would be called Steady State. I need to look at this again. Apologies for any confusion.

  2. Thanks, Gary, and no worries. Would love to hold a "steady state' at 106%+ of FTP regularly! Great read!