Calculating Swimming Training Stress Score (TSS)

Don’t know what TSS is?  It’s basically a way to measure training workload.  Every workout has it’s own TSS based on intensity, duration, etc.  Training Peaks software will calculate TSS for every workout and will keep track of accumulated TSS as the training weak progresses.  Calculating TSS for biking is pretty easy for Training Peaks, especially if you have a power meter.  Even with running, Training Peaks will use HR data to determine the TSS. However, with swimming, there is minimal data to calculate TSS.  Yet, that doesn’t mean it can’t be done.  Training Peaks walks you through here. Note, if you need more basic information on TSS, you can find it here: What is Training Stress Score?”

“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.”

First thing you need to do is determine your swimming functional threshold pace.  Training Peaks give you an option on how to do that below:

“The first is the straightforward timed effort, where you swim as far as possible in a given time (e.g. 30 or 60 minutes). So, if you swim for 30 minutes and cover 1000 meters, then you can use the value of 33.3 m/min. as your FTP. Since the actual FTP is closer to the one-hour effort, it might be more advisable to perform a 60-minute test, or to take the value obtained for 30 minutes, multiply by two and subtract 2.5 percent (as most trained swimmers swim roughly 2.5 percent slower in a 60-minute maximal effort than in a 30-minute maximal effort). So again, if you cover 1000 m in 30 minutes, your 60-minute FTP would be 1900 m/hr or 31.7 m/min. This may seem like a minor difference, but due to the resistive aspect of swimming, small differences can have a substantial impact.”

Another popular method is, after a warm-up, swim 1000 yards and record your time.  From that you can calculate you FTP.  If you have a 910xt watch, you can use your average pace per 100y. 

Knowing you FTP, you can now calculate your TSS:

Calculating swim TSS

Now that you know your swim FTP, you can easily calculate the TSS for any swim workout using the following procedure:

1. Measure total distance covered for the workout

2. Determine time to cover total distance (not including rest periods)

3. Express distance vs. time in m/min to obtain normalized swim speed (NSS), which is analogous to the normalized power and normalized graded pace in cycling and running, respectively

4. Divide NSS by FT to obtain IF

5. Swim TSS = (Intensity Factor cubed) x hours x 100

For example:

Let’s look at an example of a specific workout. First, let’s suppose that your swim FTP is 75 m/minute. Next, let’s suppose you complete the following workout (remember, rest periods are not counted):

Warm-up: 200 m @ 3:20, 30 sec. rest (3:20 total)

Drills: 4 x 50 m @ 1:00, 10-sec. rest (4:00 total)

Main set: 10 x 100 m @ 1:15, 20-sec. rest (12:30)

Cool-down: 200 m @ 3:20 (3:20 total)

Total workout distance: 1,600 m

Total workout time: 23:10 (or 0.386 hours)

The average pace for the complete workout is 1,600 meters divided by 23:10 (23.16 minutes or 0.386 hours) or 69 m/min. The intensity factor for the complete workout is the average pace (69 m/min.) divided by the athlete’s functional threshold pace (75 m/min.) or 0.92. To cube IF, multiply it by itself three times (So, in this example, 0.92 x 0.92 x 0.92). So the TSS for the workout is So the TSS for the workout is 0.778 x 0.386 hours x 100 = 30.1.

It should be noted that swim TSS does ignore rest periods, which is not the case with biking and running.  Also, it ignores different swim strokes.  Finally, it ignores flip-turns vs. push-offs. 

Now I’ll apply this to one of my training swims:

Based on the data in the screen shot below, my calculations are as follows:

Duration: 38.01 minutes = .634 hours (will use this in a bit)

Distance: 1450 yards

Distance / Duration = 1450/38.01 = 38.14 average pace.  (I am not sure why it’s different than the screenshot.  Maybe because I had kick sets in there, which my Garmin treats as a rest period.  Thus I have to manually enter the distance for kick sets).

My FTP = 41.12min/mi

Intensity Factor = average pace/FTP = 38.14/41.12 = .928

TSS = Intensity Factor Cubed x Hours x 100

.928 cubed = .799 x .634 x 100 = 50.66 TSS