Training Stress Scores

Hey Team,

One reason I love training with a power meter is because the data that it produces can give you great insight into your fitness as well as your training. So far, we have discussed a variety of Power Zone Training concepts such as Functional Threshold Power (FTP) and Power to Weight Ratio. In this post, I would like to highlight yet another useful training tool derived from Power Zone Training called “Training Stress Scores” (TSS).  

Achieving Results

In addition to the intended purpose of each cycling workout, you often hear me state that it’s “The duration (or length) and intensity of the intervals that drive the desired results.” While what we certainly feel first is the fatigue caused by the intervals, once we recover, we realize (or see) the resulting fitness improvements. This same concept applies to your overall training as well. Wouldn’t it be nice if we could do one workout, go to bed, and wake up with the results that we wanted? For example, what if we could complete one hard workout, and 24 hours later, we are ready to take on a 100-mile (or century) ride. Unfortunately, our bodies don’t work that way. Instead, we have to train and control fatigue over time to achieve results. To avoid injury or burnout from excessive fatigue, monitoring what we do and how often we do it matters. 

Defining Workload

Whether it’s simply to improve our health or to prepare for an Ironman, fitness improvements are driven by three training factors: 

·     Duration: The length of your training sessions

·     Frequency: How often you train

·     Intensity: How hard you work during your training sessions

When these three factors are combined, it is called your “workload”. Workload can be used to describe a single workout or a series of workouts over a specific period of time. When our workload increases, our fitness and level of fatigue increases. When our workload decreases, our fitness and level of fatigue decreases. However, fatigue decreases much faster than fitness at first, allowing us to control fatigue by balancing our workload with recovery. The next question is then, how do we monitor our workload? 

We often speak about our training in terms of how many miles we ride in a week, or how many days a week we spend riding, or how much saddle time we have logged. But notice how these descriptions do not cover intensity but only address frequency and duration. We have a hard time incorporating intensity into descriptions without saying general things like, “speed work” or “intervals” etc. Thus, we are not monitoring our training with three factors, frequency, duration, and intensity in mind. This is where TSS come in.

Training Stress Scores

TSS, developed by Dr. Andrew Coggan and Hunter Allen, combine duration and intensity of each workout into a number. This number can then be considered by itself or added together with other TSS over a period of time to determine how much training stress has been placed on our bodies. By quantifying the intensity and duration of each workout, coaches can give their athletes TSS to target in workouts and/or develop workouts that achieve a specific TSS number. This gives coaches the ability to plan and monitor all three training factors. The concept of TSS not only applies to cycling but also to other sports including triathlons, swimming and running. For the purposes of this post however, we will use cycling as the target sport.

Instead of going into the mathematical details behind TSS, I want to delve into the variables that make up the TSS equation. If you are interested in learning more about the mathematics behind TSS, please refer to Training and Racing with a Power Meter. The inputs to the TSS equation include: 

·     Functional Threshold Power or (FTP): An estimate of the Average Power the rider could sustain for one hour

·     Normalized Power: Adjusted average power that better accounts for the physiological demands of a workout

·     Workout Duration: The length of the workout (in seconds)

·     Intensity Factor: Normalized Power divided by Functional Threshold Power (or FTP) 

Examples

  1. 60 mins spent at 100% effort (or FTP) is equivalent to 100 TSS*
  2. 90 mins spent at 100% effort (or FTP) is equivalent to 150 TSS
  3. 60 mins spent at 95% effort (or FTP) is equivalent to 95 TSS
  4. 90 mins spent at 95% effort (or FTP) is equivalent to 142.5 TSS

* Note: A maximum of 100 TSS can be accumulated at 100% effort in one hour. Many times, workouts are completed at less than 100% effort. Thus, you can gain more than 100 TSS in a given workout but no more than 100 TSS in any given hour.

Recovery

Recovery is where our bodies shed fatigue and are able to positively respond to training stress. That said, different amounts of training stress will require different amounts of time to recover. The following are generally accepted assumptions about the recovery necessary from a ride of a given TSS:

  • <100 TSS = Low (Easily recovered the next day)
  • 100-200 TSS = Medium (Some residual fatigue present the following day, gone by the 2ndday)
  • 200-300 TSS = High (Residual fatigue usually present after 2 days)
  • 300-400 TSS = Very High (Residual fatigue usually lasting 2-4 days likely)
  • >400 TSS = Epic (Residual fatigue requires 5 days to dissipate)

Note: Other factors may delay your recovery including not getting adequate sleep, excessive stress from work/life, performing other workouts in addition to cycling, improper dieting, etc.

How to Use TSS

A given weekly TSS total of 300 may seem difficult for a less conditioned cyclist and easy for a more conditioned cyclist. As the less conditioned rider trains more, 300 TSS becomes easier and she is then able to comfortably accumulate more TSS points within a given week. The ability to take on more TSS over time serves as proof that her fitness is improving.

Once you become comfortable monitoring your own TSS, you can to start to use TSS to identify patterns in your fitness and plan future training. For example, how many weeks can you handle incremental increases in accumulated weekly TSS without needing a week to recover? For those that want to simply maintain their fitness, what weekly TSS do you want to target to ensure that you do not over or under do it? Before a big event or race, what peak weekly TSS do you want to achieve before you start to taper and prepare for your event? 

TSS can help athletes and coaches answer these questions and fine tune their training so that they are peaking at the right time. TSS can also help coaches steer their athletes away from injury when too much training stress is applied too soon. While I will certainly discuss this more in future posts, this should give you an idea of how TSS can be used to your advantage.

From a training perspective, planning out your weekly or even annual TSS goals is a great way to get started. Of course, this is also something you can outsource to your coach. For example, Joe Friel does a great job of providing guidance in his book, The Cyclist’s Training Bible. Here is an example of how one could plan out their weekly workouts based on TSS:

As you can see, there is a lot of insight we can gain from monitoring and even planning out our training using TSS. That said, remember that TSS do not give us insight into the specifics of the fitness that is being built. For example, the workouts to complete when training for a criterium bike race are very different from those for a century ride. So, while the TSS for two different athletes training for two different events could be the same, their workouts, and thus the specifics of their fitness being developed would be very different. This is yet another part of your training to consider or have a coach to consider for you.

If you are interested in learning more about TSS, links to references I used in this post can be found below. I hope you find the concept of TSS as useful as I do in our quest to continue training smarter and removing guesswork.

Training and Racing with a Power Meter

The Power Meter Handbook

The Cyclist’s Training Bible