Training Stress Score (TSS)
TSS is basically a measure of how hard you are working. It is based on Intensity Factor (IF) and the length of time of the training session (or race). Knowing your heart rate numbers helps make this a bit more accurate, especially in determining the IF score, but power (if using one on the bike) or RPE (rate of perceived effort) can also be used. I personally like to use RPE in my head and then compare it to the IF reading after a session to see how close the result was. For example, if I have a run scheduled and know it is for 60-70% RPE, my IF score should be between .6 and .7. If my IF is a .9 that would tell me that (1) my RPE is wrong (entirely possible), or (2) my heart rate entries are off in the TrainingPeaks software account.
So why does TSS matter?
It comes down to knowing how hard you worked outside of how it felt. We all have those runs that felt like we were in quicksand. Sometimes TSS can back that up with hard numbers, but also it can tell you that it might have felt hard, but actually wasn’t that taxing on your system. It can also tell you when a specific workout was too much (i.e. a hill repeat for 10 splits might be too much, but the same workout for 5 splits might be fine). Knowing that “tipping point” is helpful and reviewing TSS can help identify that point.
Acute Training Load (ATL) and Why it Matters
ATL is the measure of FATIGUE over the last 7 days of training based upon the frequency, duration, and intensity of the workout sessions. Knowing this number helps identify upcoming needs of recovery. Watching TSS as it increases can cause ATL to jump up very fast, which eventually leads to your body failing you.
Chronic Training Load (CTL) and Why it Matters
Basically the same measurement as ATL, CTL is taken over the previous 6-weeks. Progressive training, if done correctly, will result in an increase in CTL, which is what you want to see. It is the relation of CTL to ATL that is important, and bring us to the next item.
Training Stress Balance (TSB), or Form, and Why it Matters
As stated, TSB is the relation of CTL to ATL at any given point. So taking CTL and subtracting ATL give you a number either positive or negative (the formula is TSB = CTL – ATL). A negative TSB (meaning ATL is higher than CTL) can mean you are over-fatigued, and a positive means you are “fresh”.As with most thing, however, this can be misleading and is subjective. Your goal is to hit an event with a positive TSB, meaning you are fresh and ready to race, but some people race better with a negative TSB. Finding that “sweet spot” is key to planning and measuring training. Once again, where a coach can come in handy. I personally, for my own racing, try to come into an event between -3 and +10. When I have raced with a number below -3 I have found to be tired very quickly, and the same for anything over +10, where I feel very strong at first but tire out fast.
The Performance Graph
So, for some real-world examples consider these graphs:
In the performance graph above you can see my cycling results since January 2019. The circled result is the 52-mile ride I did on May 4th. At this point in my training, I had a CTL of 15 and an ATL of 44, meaning in the previous 7 days to this ride I was doing quite a bit of high TSS training. My TSB (form) was a -3, right where I like it to be, so it resulted in a ride that was hard at the end, but for the first 35-40 miles I felt really strong.
In this performance graph, I am only looking at my swims in the same time frame. what you can see here is I was doing quite a lot of swimming in the first three months and that has tapered off a bit. In this instance, I rarely use a heart rate monitor so my TSS as it uploads shows a zero, and even when it does show one it hovers around 10. This is due to my heart rate not being that fast while swimming and the duration being in the 60-minute range. My TSB is also in the 0.0 range, meaning most swims are not taxing me that much, so I need to “up my game” as far as effort goes.
Not to leave running out I am using a client’s run performance profile (because I have not been running as much as they have). This client has a race coming up this week and has been training hard for it. All is evident from what we are seeing here; a steady climb of CTL (the blue portion), a steady decline in ATL (the pink line due to tapering), and an entry into race day with a TSB of +11. They should, according to this graph, do very well in this race.
The Meaning of it All
In the end, numbers like this are there to help you quantify your training plan and how you are progressing. As I wrote in the first section, an expert level knowledge is not needed to make the most of this, but a working ability to see the numbers or the graph, and know how you are doing goes a long way in helping you work with your coach to achieve your final goal, which is always to do well in the event you are training for, whatever that means for you.
If you have any questions about your personal numbers and are not currently being coached by us, please reach out and we can guide you through some basic understanding of it. There are also some great guides out there online (try the TrainingPeaks blog or the book Triathlon 2.0 to start). We are always here to help you.