Calculating TSS for Swim Workouts
2 November 2008
In his latest article, Matt Fitzgerald teams up with Stephen McGregor, PhD, to describe a method of calculating Training Stress Scores for swim workouts. Triathletes using WKO+ to monitor their training will appreciate being able to include their swim workouts in their fitness and training overview.
TrainingPeaks WKO+ automatically generates training stress scores (TSS) for bike rides uploaded from a power meter and for run workouts uploaded from a speed and distance device. Triathletes who use WKO+ and appreciate this feature often wish that the program could do the same for swim workouts. Unfortunately, the swimming equivalent of a bike power meter or run speed and distance device does not yet exist. However, you can calculate TSS for your swims manually using a method we’ll describe in this article.
Why not simply use the same calculation for swim TSS that is used for running, in which the metric of pace is also used to quantify the training load? Because water presents more resistance than air, so the physiological stress of swimming increases with increasing swim speed faster than the physiological stress of running increases with increasing running speed.
The simplest, if not the most accurate, way to account for this difference in calculating TSS scores is to weight the “intensity factor” of swim workouts differently than it is weighted for run workouts. Specifically, we suggest, it should be cubed as opposed to squared.
To read more about exactly how to calculate your TSS score for swim workouts, including an example workout that walks you through the steps of the analysis, please see the complete article on our TrainingPeaks homepage Archived Articles.
Update! While the authors of this article worked to develop this formula independently, their analysis has been confirmed by Paul Newsome from Swim Smooth, who calculates Swimming TSS in a similar manner. Learn more from him at www.swimsmooth.com
2 Responses to “Calculating TSS for Swim Workouts”
November 3rd, 2008 at 11:54 pm
Thanks for the Article Matt – Very informative.
I have been using a spreadsheet that I have created up until this point, which effectively works out the TSS per individual set from the IF of the pace, then sums it for the total workout. Same methods as you use in your method, only still using the IF squared. It calculates other aspects like VI, total rest etc.. as well which I copy\paste into TrainingPeaks under the notes.
I am curious about what you mention when it comes to cubing the IF rather than squaring it. This will definitely give a larger weighting to sets that are performed above threshold pace, but it will underweight the workouts that fall below FTP. Would you still suggest using the cube if I am calculating TSS per set? I can see how it might compensate over the whole set, but would you still recommend this principle when taking into account the various “spikes”?
Thanks,
Jean
March 16th, 2009 at 9:51 pm
Hi Matt – Thanks for this. I have been thinking about sTSS for some time. I am not sure the cubing of the IF is correct.
At the core of the TSS concept is Power (not speed). And in the case of swimming, Power is proportional to velocity**2.5 (at least approximately).
Now TSS is proportional to IF squared (when IF is based on power).
So putting these two ideas together, shouldn’t the sTSS be calculated using your speed based IF to the power of five.
Yes, I know this seems like a huge power, but I have noticed in my swim work-outs that my speed range is very narrow (much narrower than the power range on the bike. e.g. it is much easier for me to hit power levels 3 or 4 times my FTP, but there is no way my swim speed would vary that much).
So while the cubing has a good feel to it, I think IF (based on swim speed) to the power five is a little more scientific.
What are your thoughts?
Thanks Rob