CTL ,ATL, TSB, TSS? - Understanding Performance Management Metrics
Various training apps can be used to monitor, plan and analyse an athletes workout and performances. Most of them regurgitate various metrics (discussed below) that many athletes (and some coaches!) don’t understand or understand vaguely or by word of mouth. Training peaks produces the following metrics which I will now discuss, dissect and provide useful analogies to (see the end of this article for my English Sword analogy):
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1) TSS (Training Stress Score) Also known as - WORKOUT STRESS
This is the big daddy, the metric that determines all the other metrics to be discussed in this article. Training stress is a score that is produced after each workout. It essentially tells you how hard or easy that workout was and its stress on the body. The greater a TSS reading a greater stress that workout has had on body (in theory).
TSS is produced by using your either Heart rate, power or speed data for a given exercise in combination with specific zones set for these metrics. The zones set are usually based off previous test results to determine a specific zone e.g FTP (functional threshold power test for a bike is: 0.95 x your average power in watts for 20 minutes all out gives, this is one way to gauge your FTP) This result is the imputed into the app and zones are created based on percentages of the FTP result. These ‘tests’ all have flaws of their own (see my 2nd article ‘Is CTL (Chronic training load) a good measurement for tracking fitness and ultimately event performance') and so these metrics discussed should be used wisely and with caution.
Key questions: What is the most effective TSS per training session- this is dependant on: the athletes goals, fitness levels, where they are in their training year, month week and specific day relative to their goals, type of session, (again see article 2 as to using with caution)
2) CTL (Chronic Training Load)
Also know as- FITNESS
This is what most people refer to as their fitness levels. CTL is your average TSS over a 42 day period.
So in theory the more you train, the more TSS produced, the higher your average TSS levels are going to be over a 42 day period, the higher your CTL levels and so the higher your fitness. The next conclusion would be, so then the better your performance come race day. In theory, yes, but see article 2 how this principle isn’t clear cut.
3) ATL (Acute Training Load)
Also know as FATIGUE Your average TSS over the past week (7days).
So the harder the previous days/weeks /months workouts have been the higher this score. This rises quicker and is much more responsive than CTL (Fitness) due to it being the average over 7 days. In theory a carefully planned programme avoids too many unnecessary high spikes in fatigue that take too long of a recovery period to come back from. You can’t use your high fitness levels if your fatigue levels are sky high. In essence sky high ATL levels result in a hugely negative FORM figure and form is essentially your FRESHNESS. (See my English Longsword Analogy after para 4 which highlights this point)
A higher level of fatigue is often reflected in your FORM (TSB) reading (to be explained below). So your TSB is the one of the more important metrics to monitor in relation to monitoring fatigue levels.
4) TSB – (Training Stress balance) Also known as FORM
How ready and fresh your body is to use its fitness levels.
The lower this figure the greater state of fatigue your body is in. Your TSB is essentially your FITNESS level minus your FATIGUE level. So a higher fatigue figure the lower your form. Shed this fatigue (get ATL lower), by resting and having de-load periods/ recovery periods, and your form will increase and essentially this is the process for tapering for an event. (again in theory!)
5) Summary
My English Long Sword analogy:
You want the longest strongest sharpest sword possible for battle. You must heat it up, stretch it, hammer and mould it and then let it cool. Too quick of a process, too much stretch too soon (e.g too much TSS and training) the sword will get too hot, molten/ thin and snap/ melt during the process (illness , injury burnout, lack in motivation etc). Too little cooling time (recovery and de-load periods) the sword will not cool down enough and so its length will not be able to be used in battle (too high the heat in the metal (ATL -fatigue levels in your body) needs to reduce before the length ( your FITNESS CTL figure ) can be realised.
Trying to use a molten sword in battle would be pointless. The same goes for fitness. Trying to realise and use your fitness levels with a huge level of fatigue and a low form figure just wont work.