Running Stress Score (RSS) is a single number to help runners understand their day-by-day training. It takes into account the volume and intensity of your training session to give you a single number, or “score.”

The primary input to RSS is running power (collected each second) along with the time
spent at different training intensity levels and can be calculated as follows:

RSS for each second of your run = a * (one second power / Critical Power)^b

where a and b are both constants developed by sports physiologists.

The Running Stress Score is similar to TSS (training stress score) which allows you to compare the stress of workouts of various duration and intensities. The difference between TSS and RSS is small, the difference coming from the fact that the equation for RSS is intended to account for the additional biomechanical stress put on your body from running whereas cycling is largely aerobic stress.

RSS is calculated by comparing your power during your run with your Critical Power. Therefore, accurate Critical Power is essential for RSS calculations. If you have auto-CP disabled, it is recommended to repeat the Critical Power test every 4 - 6 weeks.

In the TrainingPeaks platform, the term Training Stress Score (TSS) is used. Here is how you would calculate TSS:

TSS = (duration of workout in seconds x NPx IF)/(FTP x 3600) x 100

The 42-day average shown in PowerCenter is using the unweighted average whereas the 42-day average shown in the mobile app is using the weighted moving average.

The RSB in PowerCenter is still calculated using the exponential and will be the same RSB that is shown in the mobile app, the change only applies to the averaging that is shown in the My Training Chart. The averaging method for all metrics (RSS, distance, duration) in the My Training Chart is unified, all use normal averaging.

The reason why the weighted average is shown in the mobile app but not shown in PowerCenter is due to the combination of the Coach’s View feature (multi-user support) and the option to select custom time ranges within the My Training chart on PowerCenter. PowerCenter My Training Chart uses a normal average instead of a weighted average to make the flow fast enough to support multiple users.

PowerCenter calculates various metrics and training plans based on your critical power. Critical Power (threshold power) represents the highest power that a runner can maintain in a quasi-steady state without fatiguing, where the duration may range from 30-70 minutes, depending on the individual. You can read more about Critical Power here:

Critical Power

If you use the default settings of the Stryd system, Stryd will automatically calculate your Critical Power number based on your run data. You will get an initial estimate of your Critical Power after three runs. As long as critical power is not is set in PowerCenter (i.e. 0), your RSS values will be 0 since power is critical to determine your RSS. RSS is a single number to help runners understand their day-by-day training. It takes into account the volume and intensity of your training session to give you a single number, or “score.”

Some Stryders have noticed that RSS for their trail runs is lower than expected. For the RSS calculations, PowerCenter considers time spent in each power zone. If power during your trail run is the same as a comparable run on the road, RSS will be the same.

If your trail run has ups and downs, note that Stryd does adjust power while climbing or descending. Some Stryders have experienced that power hiking results in lower power numbers than running, and that it is challenging to maintain power running downhill. This might mean you are not in the power zones you might expect.

Stryd does currently not accommodate for surface differences. If you are on sandy or rocky trails, your effort may be higher than Stryd can record.