Training Stress Score (TSS)

Training Stress Score (TSS) was developed by TrainingPeaks as a way to quantify the stress of a particular workout or portion of a workout. By giving each workout a TSS value an athlete and/or coach can see how much stress each workout puts on an athlete and use this information to guide training specifics, as well as recovery.

Calculating TSS for cycling requires the use of a powermeter and an accurate threshold power or FTP. Riding at a certain percentage of FTP sets the level of intensity and that combined with duration allows for the calculation of TSS. In very simple terms, if you ride at your FTP for 1 hour you would accumulate 100 TSS but you could also ride for 2 hours at a tempo pace and accumulate 100 TSS. Both would require the same amount of recovery in theory but can vary slightly depending on many individual factors.

In class, we only have an hour to build our TSS value and since we do a progressive warm-up and a cooldown the TSS value is typically from 55-75. If you are doing an event that requires multiple hours on the bike you can roughly calculate that you will be creating 40-60TSS per hour. So a 4-hour ride or race would roughly be 160-240TSS, which would require some long rides to prepare properly for this type of event.

As for recovery, TSS can be used to establish how much you may need to fully recover from an effort. A very rough estimate is 1 day for every 100 TSS, with athletes over 40 years of age requiring more time to fully recover. Since most of us who work can only workout for 1 maybe 2 hours per day the TSS value is probably right around that 100 TSS allowing us to workout day after day and feel pretty good. Now TSS is also cumulative day to day, for a weekly, monthly, and yearly total. Too much TSS without enough recovery can lead to overtraining and a decline in performance. So make sure you get in enough recovery each week to accommodate the TSS for the week and keep making gains from your workouts.

Normalized Power (NP)

Figuring out how hard a particular workout or effort is can be difficult for most sports but for cycling, power meters have given us a very direct objective measurement of the actual work an athlete is doing. In order to gain fitness or prepare for an event, an athlete must create stress and then recover from that stress to get stronger. The main components of “stress” are intensity, duration, and frequency.

Taking Average Power (AP) by simply averaging the highs and lows of an effort over a given duration is pretty simple to understand and calculate and on the surface seems like a great way to capture how hard an effort is over a particular duration. But, it’s actually somewhat limited in its application.

Average Power v. Normalized Power

For example, if a rider does a 1-hour ride and keeps a steady pace of 200 watts the entire time the average power would be 200 watts. The same rider could do the same 1-hour ride but this time fluctuates the power back and forth spending 5 minutes at 300 watts followed by 5 minutes at 100 watts. This type of ride would also create an average power of 200 watts but 5-minute efforts at 300 watts would be much harder and thus the second ride would be more taxing or create more stress for the rider. Normalized power can be calculated using a complex algorithm that takes into account the variance between a steady workout and a fluctuating workout.

Normalized power(NP) tries to give an accurate assessment of the work done and the quantity of the physiological tax paid for each workout or effort. For a highly variable workout, NP can be much higher than average power, whereas, for a very steady workout, NP and AP are equivalent or very close together. A relatively high NP shows that the workout had a lot of variation, and was harder physiologically than what average power may reveal. By having a more accurate measurement of the stress on the body a rider or coach can make adjustments to training and base recovery needs on a better measurement. Since there are a lot of individual factors that come into play with each athlete’s situation, anything that can enable us to better quantify “stress” means we can plan workouts and recovery better to meet a particular athlete’s needs and maximize time to help better enable them to reach their goals.