# Training Stress Scores (TSS) Explained

TrainingPeaks uses several physiological metrics to quantify the training stress of a particular workout or portion of a workout.  Below are each of the training scores, how they are calculated, and the level of accuracy for each metric.

## Training Stress Score (TSS)

• Applicable Workout Types: Bike or Rowing with Power Meter only.
• Accuracy Level: power-based TSS (compared to hrTSS, tTSS, or TSS*) is the most accurate method of calculating a Training Stress Score, and is the default method for Bike workouts when there is enough data present to calculate
• Requirements to Calculate: Powermeter data file containing time series duration and power data, power threshold (FTP) set in Power Zones section of My Settings
• What is TSS? Training Stress Score (TSS) is a composite number that takes into account the duration and intensity of a workout to arrive at a single estimate of the overall training load and physiological stress created by that training session.  It is conceptually modeled after the heart rate-based training impulse (TRIMP).  By definition, one hour spent at Functional Threshold Power (FTP) is equal to 100 points.
• Normalized Power (NP): An estimate of the power that you could have maintained for the same physiological "cost" if your power had been perfectly constant, such as on an ergometer, instead of variable power output.  NP is used to calculate TSS.

• Intensity Factor (IF) for TSS: For any workout or part of a workout, the ratio of the Normalized Power to the rider's functional threshold power, which gives the user a relative intensity in relation to their threshold power. IF is used to calculate TSS.

## Running Training Stress Score (rTSS)

• Applicable Workout Types: Run only (TSS can not be calculated for bike workouts from speed)
• Accuracy Level: rTSS is the second most accurate method of calculating a Training Stress Score, and is the default method for Run workouts when there is enough data present to calculate
• Requirements to Calculate: Workout time series with pace and elevation data, user threshold pace for run/walk (entered in pace/speed zones)
• What is rTSS? Running Training Stress Score (rTSS) is similar to Training Stress Score (TSS), but instead of being powermeter based, it is based on pace.  Since running pace is a function of power, and for most runners, speed or pace is the measure of greatest interest, we can use the same principles applied in the TSS system to quantify training stress in running. In particular, the elements of the normalized graded pace (NGP, see below), relative to the functional threshold pace. Coupled with the duration of the workout, we can determine an appropriate rTSS score for each workout. rTSS is a metric that can only be used in running workouts, as the algorithm only accounts for the unique physical demands of running.  Further details on rTSS can be found here:

• Normalized Graded Pace (NGP): The adjusted pace reported from a global positioning system (GPS), or other speed/distance device, that reflects the changes in grade and intensity that contribute to the physiological cost of running on varied terrain. For more information on NGP, please see:
• Intensity Factor (IF) for rTSS: For any workout or part of a workout, the ratio of the Normalized Graded Pace to the runner's functional threshold running pace, which gives the user a relative intensity in relation to their threshold pace. IF is used to calculate rTSS.

## Swim Training Stress Score (sTSS)

• Applicable Workout Types: Swim only
• Accuracy Level: sTSS is in Beta, so we are still working through exactly how accurate it is.  It will be used as the default method for swim workouts when there is enough data present to calculate.
• Requirements to Calculate: Workout moving duration, distance, user threshold speed for swimming (entered in speed zones)
• What is sTSS? Swim Training Stress Score (sTSS) is based on your functional threshold swim pace, total distance covered, and total moving duration (duration not including rest periods).  For more on this metric and how it is calculated, please see:
Calculating Swimming TSS (sTSS)

## Heart Rate Training Stress Score (hrTSS)

• Applicable Workout Types: All workout types
• Accuracy Level: hrTSS is quite accurate with steady-state effort workouts, but is less accurate for workouts with highly fluctuating efforts.  hrTSS will only be used if there is not enough data to calculate TSS, rTSS, or sTSS, and the below requirements to calculate are met.
• Requirements to Calculate: Workout time series heart rate data, user threshold heart rate (entered in heart rate zones)
• What is hrTSS? Heart Rate Training Stress Score (hrTSS) is based on time in heart rate zones (based on users' lactate threshold heart rate) and is not as accurate as Powermeter based TSS or running pace based rTSS.  TrainingPeaks uses the table found in the article below for calculating heart rate training stress score:

## TRIMPS Training Stress Score (tTSS)

• Applicable Workout Types: All workout types
• Accuracy Level: tTSS is in Beta, and is considered to be the least accurate method to calculate a training stress score.  We have so far discovered that like hrTSS, it is best used with steady-state effort workouts, as it is not very accurate for highly fluctuating effort workouts.  tTSS will only be used if there is not enough data to calculate TSS, rTSS, sTSS, or hrTSS, and the below requirements to calculate are met.
• Requirements to Calculate: Workout duration and average heart rate
• What is tTSS? TRIMPS Training Stress Score (tTSS) is based on average heart rate, the total duration of the workout, and the person's physiological heart rate properties (resting heart rate, threshold heart rate, and maximum heart rate).

## Manually entered or estimated TSS - (TSS*)

• An asterisk next to TSS indicates that it was manually entered instead of calculated from the workout data.