Tuesday, January 28, 2014

What is Training Stress Balance (TSB)?

by Hunter Allen, PCG Founder/CEO and Master Coach

PCG athlete Carter Jones (coached by Dr. Stephen McGregor) was the polka dot jersey holder
in the 2013 Amgen Tour of California.

When I was a pro cyclist, we all talked about having “good form”—the legs feeling great, the days of “no chain,” when we were just “on,” and when we knew no one was going to beat us that day. We all knew what it was, but we could never really describe it. What exactly is “form?” Where does it come from, and how do we actually acquire it? How do we achieve form exactly on the day or period of time that we want it? How do we know that the training we’re doing now will give us the necessary “peak” when we want it? Are we training too hard? Are we training hard enough? Are we training in the proper training zones? Are we getting enough variety in our training to make sure each physiological system is improving? I had to answer all these questions when I was racing and again as I developed detailed training programs for my clients.

When the power meter came along and I started thinking about how to best use a power meter to build training plans for my athletes, I wanted to be able to quantify each training “dose,” because understanding the training dose and the resulting response is the only way to really know the exact “ingredients” needed for success. The advent of the power meter has allowed us to quantify exactly the training response. Now that we’re able to download a digital record of each ride and analyze it, we can more thoroughly understand the response to the training dose.

On the other side of the coin, the power meter also enables us to prescribe a precise training dose. Gone are the days of riding for four hours and hoping that four hours is enough to make you fit for the upcoming race. Time and distance were the only things by which we could periodize our training load until the introduction of the power meter. Heart rate, rate of perceived exertion, and VO2Max are responses to a training dose, or watts. Now, as a coach, I can be more specific with the training I prescribe to my athletes. Do 45 minutes at 89% of your functional threshold power (FTP) each day, and in 4-6 weeks we’ll see the response.

With a power meter we’re easily able to see the results of our hard work over time, but as a coach I really needed to be able to quantify the exact training dose more simply than 2 x 20 minutes at FTP and 6 x 5 minutes at VO2Max power. I needed a score.

I shared all this with Dr. Andrew Coggan, a great friend and brilliant sports scientist with whom I share many of my training/coaching ideas. Within two weeks he came back with “training stress score,” a method of giving each ride a score based on the exact training load or training dose achieved. Dr. Coggan’s formula was based on Dr. Bannister’s work on a heart rate-based score called TRIMP, “Training Impulse.”

Training stress score (TSS) was based on the simple premise that you score more points the more time you spend at your functional threshold power (FTP) and above it. Intensity must also be accounted for, so a measurement of intensity was given for each ride, as well, which Dr. Coggan called the intensity factor (IF). To set the standard, an hour at FTP would score 100 TSS points and an IF of 1.0. With the creation of these two metrics, we could now understand the training dose and analyze the training response with software by tracking fitness changes over time.

As a coach, I can make anyone fit. That’s not too hard; just do these intervals, ride this much, push yourself this hard, and the fitness will be there. Fitness isn’t form, however. It’s lacking a key component.

I once asked a several-time Tour de France winner what he thought of as form. He’d been “on form” many times and knew inherently what it was when he felt it, but he couldn’t describe it. At the end of the Tour de France, he wasn’t on form (he was fatigued and severely over-reached from the training state), but he had lots of fitness! On the other hand, he currently isn’t very fit, although he’s “fresh” from not exercising as much, so again he doesn’t have form. Those two things are the keys to form, which Dr. Coggan defines as fitness + freshness. The correct balance of fitness and freshness creates this magical thing called form, and understanding this simple equation makes it possible to manage form and create it at the right time.

There are two components to fitness: chronic training load (CTL) and acute training load (ATL). Chronic training load is the load (dose) of training over a longer period of time (every training ride you’ve done in the last six weeks). Acute training load (ATL) is the training you’ve done in the last seven days. The training you did six weeks ago and the training you did last weekend are both impacting you now as you read this.

Both CTL and ATL help determine your level of fitness and freshness. By balancing them correctly and carefully, you can create a high level of fitness and a high level of freshness, thereby managing form. We call this “training stress balance” (TSB). When your TSB is a positive number, you’re becoming fresh, and as long as you have fitness backing you up, you could have a peak performance. The higher your TSB, the greater your freshness. When your TSB is a negative number, you’re not very fresh and are in a fatigued state. The more negative the number, the more fatigued you’re likely to be. We use the performance manager chart in TrainingPeaks WKO+ software to predict peaks of fitness and when you need to rest to prevent overtraining.

By understanding these simple concepts and using your power meter, you are well on your way to exceeding your goals this year. May your FTP always increase!

Important Terms and Definitions:
  • FTP: Functional threshold power. The best average power that you can maintain for one hour.
  • TSS: Training stress score. A way to quantify the stress of each ride. An hour at FTP equal 100 TSS.
  • IF: Intensity factor. The intensity at which you work based on your FTP. When working at FTP, this will equal an IF of 1.0.
  • CTL: Chronic training load. The training load that encompasses a longer time period, most likely 21-42 days.
  • ATL: Acute training load. The training load that encompasses the most recent training load, most likely the last 3-14 days.
  • TSB: Training stress balance. The balance of CTL and ATL creates either a positive (+) or negative (-) TSB.  A positive TSB will most likely predict a peak performance.

Hunter Allen is a USA Cycling Level 1 coach and former professional cyclist. He is the coauthor of Training and Racing with a Power Meter and Cutting-Edge Cycling, co-developer of TrainingPeaks’ WKO software, and CEO and founder of Peaks Coaching Group. He and his coaches create custom training plans for all levels of athletes. Hunter can be contacted directly through www.PeaksCoachingGroup.com.


  1. Nice summary. My biggest question when it comes to TSB isn't so much about the T or the S, but the B. Is there any guidance on what an ideal balance is? If I am hitting -30 on my TSB is this a sign of ramping up the workload too quickly and a set up for NFOR or overtraining? Should I strive to maintain a TSB in the -5 to -15 range indicating a slowly progressive, sustainable increase in workload. Should my TSB always cross into positive territory at the end of a rest week going into a new training block? Does it matter if I feel good and don't have signs or symptoms of overtraining (kind of like using a wide-angle RPE to judge performance effort over days to weeks?


  2. Thanks for reading, Tristan! Hunter Allen and Dr. Coggan wrote a section in their book (Chapter 8, Pages 156-158) regarding exactly this question. Maybe these graphics will help:


    (Might want to save these images, as the links are temporary.)

    You can also purchase the book itself here: http://bit.ly/1beLE7L.