Why don't TrainingPeaks and WKO4 agree on my swim TSS?

Some workouts seem to produce a different TSS in WKO4 than in TrainingPeaks. Why? Both apps calculate TSS and IF according to these standard formulas:

  • NSS = distance / (timeTotal * 3600); //in m/sec
  • swimIF = nss / threshold
  • swimTSS = intensityFactor * intensityFactor * intensityFactor * timeTotal * 100

The difference between the two is that TrainingPeaks does not include resting time when calculating the average pace of a swim. Unlike work, however, TSS is a metabolic score; resting affects stress, because more resting results in less stress.

For example, a person who swims 2100 meters for 45 minutes straight accumulates more stress than someone who swims 2100 meters in an hour with 45 minutes of swimming and 15 minutes holding onto the wall. In TrainingPeaks, both hypothetical swims would accumulate the same stress, while in WKO4 the swim with the 15 minutes of resting would produce a lower TSS because it is an easier swim than swimming 45 minutes continuously.

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