Fitness is a Science


If you didn’t know it already, fitness is a science and there are many tools that you can use to measure progress. One of them is called Chronic Training Load (CTL), which is an exponentially weighted average of the last 42 days of training. In simple terms, it’s your current degree of fitness. It goes up when you increase the frequency and intensity of your workouts. It goes down when you decrease the frequency and intensity of your training. Ideally, it should be upward trending.

After every workout you have a Training Stress Score (TSS), which is a measure of how difficult it was. Data such as power and heart rate is used to calculate the training effect. An easy session (i.e. jogging) will be 25% or below your current CTL and a hard workout (i.e. sprints) will be 50%-100% above your current CTL.

Fatigue (ATL), is calculated by using a weighted average of your TSS scores. It determines how tired you should be based on accumulated workout volume and intensity.

Lastly, Training Stress Balance (TSB), is calculated by subtracting your fatigue (ATL) from your current fitness (CTL). It is an indicator of your projected race readiness. While negative numbers are okay in training (-10 to -30), anything in positive territory is ideal for racing because it means you’re fresh and well rested.

As race day approaches, CTL and TSB should be inversely correlated, due to a reduction in training volume and intensity during the taper period. Here is a chart before I started tapering for 70.3 Chattanooga, my CTL was 92 and my TSB was -14. 

After 10 days of tapering, my CTL dropped to 83 and my TSB rose to 16. 

My current CTL is 97 and my TSB is -23. I have a race this weekend, so I hope to bring that TSB number into positive territory, but it will be difficult because I don’t plan on tapering for this race – I can’t afford to back off now in the middle of my peak training phase for the Ironman.  

This Saturday is the Wyckoff/Franklin Lakes Triathlon! It has a special place in my heart because I did it last year and it was my first triathlon. I’ve learned so much since then and hope to improve this time around. 


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