Training load: CTL, ATL and TSB explained for coaches

Short answer: CTL, ATL and TSB are three ways to summarize a athlete's training load over time: - CTL (chronic load): weighted average daily load of about 6 weeks (42 days). It reflects how "trained" it is. - ATL (acute load): the same with about 7 days. Reflects recent fatigue. - TSB (balance or shape): CTL − ATL. If it is negative, it accumulates fatigue; if it is positive, it is more rested.

They come from Banister's impulse-response model (form and fatigue) and are indicative: they describe trends, do not decide for you (Hellard et al., 2006).

Where do CTL, ATL and TSB come from? The form-fatigue model

The idea, proposed by Banister in the '70s, is that each session generates two effects: a shape that grows slowly and lasts, and a fatigue that rises quickly and goes quickly. Performance would be the least form of fatigue. Subsequent studies showed that the response varies according to the person and the training phase (Busso, 2003), and that the model has limitations to predict the performance of an individual (Hellard et al., 2006).

What this means to you: curves help you see trends and spot peaks, but they don't replace your judgment or what the athlete tells you.

Step 1: How is the load of each session measured?

You need a load number per session. The most universal and unequipped form is the sRPE (session PRE) (Foster et al., 2001):

Session load = RPE (scale 0–10) × duration (minutes)

Advantage: it serves to run, trail, bike, swimming and strength with the same unit. You can also estimate the load from heart rate or power; the important thing is to always use the same method with each athlete.

Alternative: load from clock data

Many platforms calculate the load of a session with the duration and intensity relative to your threshold (power, pace, or heart rate). The idea is that intensity weighs more than time: an hour near the threshold payments more than a mild hour. To make this data useful:

1. Up-to-date threshold. If the threshold is out of date, all the calculated load is. Test him again at the start of each block.
2. One method per sport. A bike load unit does not exactly equal one in race or swimming; it compares each athlete with himself and within the same sport.
3. Watch the sensor. In short series, heart rate reacts late and undervalues effort; power or pace usually reflects it better.
4. The same burden does not tire equal to all. Sleep, nutrition, stress and experience change the response, so it is best to cross the data with the RPE and well-being.

Step 2: How are CTL, ATL and TSB calculated?

Exponential moving media (EWMA) are used:

• CTL_hoy = CTL_ayer + (Carga_hoy − CTL_ayer) / 42
• ATL_hoy = ATL_ayer + (Carga_hoy − ATL_ayer) / 7
• TSB_hoy = CTL_ayer − ATL_ayer

(Variant: some implementations use the factor 1 − e^(−1/τ) in place of 1/τ; the result is very similar.)

Simplified example: CTL from yesterday 300, ATL from yesterday 350, load from today 480. - CTL = 300 + (480 − 300)/42 ≈ 304.3 - ATL = 350 + (480 − 350)/7 ≈ 368.6 - TSB (for today) = 300 − 350 = −50 → accumulates fatigue.

Step 3: How do you interpret them without them deciding for you?

On the acute/chronic load ratio (ACWR): was popularized to relate peak loads to injuries (Gabbett, 2016), but there are important methodological criticisms, such as mathematical coupling (Lolli et al., 2019) and the validity of the concept itself (Impellizzeri et al., 2021). Don't use it as an automatic injury light.

What errors are common when using CTL, ATL and TSB?

1. Mix methods load for the same athlete (one day sRPE and another HR).
2. Calculate with an outdated threshold: the load comes out undervalued or inflated.
3. Pursue CTL figure instead of the performance target.
4. Ignoring Force Because "no clock data": with sRPE it does count.
5. Perform without context: travel, sleep, work or stress also "charge".
6. Let an app reset the plan alone from these curves.

Real Case: How does Marc Bañuls apply it?

Real Case: Marc Bañuls, coach with more than 15 years experience. "The load curves help me to ask better questions, not to have automatic answers. If the graph says one thing and the athlete tells me another, I talk to him before I touch anything." "I ask for the RPE of each session, also of strength. It's the cheapest and the one that tells me the most."

How will you see the load in TrainingForever?

• Session load (sRPE and Garmin Connect and Strava watch data (and export to Coros and Polar)), with CTL/ATL/TSB, zones and adhesion.
• The "Need Your Attention" panel warns of sudden changes; the decision to adjust is yours.
• The AI Assistant drafts a weekly adjustment; you review it and publish it.

Frequently Asked Questions

What is CTL in training?

The chronic load: a weighted average daily load of about 6 weeks that reflects your accumulated level of training.

What is ATL?

The acute load: the same with about 7 days; reflects recent fatigue.

What does a negative TSB mean?

That the recent burden surpasses the chronicle: the athlete accumulates fatigue. It's normal in load blocks; watch it if it lasts long.

How do I calculate the load of a session without potentiometer?

With sRPE: RPE from 0 to 10 × minutes of the session (Foster et al., 2001).

Does the acute/chronic ratio predict injuries?

The evidence is discussed; do not use it as an automatic predictor.

Sources

1. Foster C, et al. A new approach to monitoring exercise training. J Strength Cond Res. 2001;15(1):109-15. PMID 11708692
2. Busso T. Variable dose-response relationship between exercise training and performance. Med Sci Sports Exerc. 2003;35(7):1188-95. doi:10.1249/01.MSS.0000074465.13621.37
3. Hellard P, et al. Assessing the limitations of the Banister model in monitoring training. J Sports Sci. 2006;24(5):509-20. doi:10.1080/02640410500244697
4. Gabbett TJ. The training-injury prevention paradox: should athletics be training smarter and harder? Br J Sports Med. 2016;50(5):273-80. doi:10.1136/bjsports-2015-095788
5. Lolli L, et al. Mathematical coupling causes spurious correlation within the conventional challenge-to-chronic workload ratio calculations. Br J Sports Med. 2019;53(15):921-922. doi:10.1136/bjsports-2017-098110
6. Impellizzeri FM, et al. What role do chronic workloads play in the challenge to chronic workload ratio? Time to dismiss ACWR and its understanding theory. Sports Med. 2021;51(3):581-592. doi:10.1007/s40279-020-01378-6

(Metadata of 1–6 verified in PubMed on 16/10/2026.)