CLT、ATL and Training Load Ratio

Training Load quantifies the stress and stimulus that training places on your body and is a core metric in structured, science-based training.
Looking at both long-term and short-term training load helps you build fitness progressively while reducing the risk of injury.

  1. Chronic Training Load (CTL)
    A weighted average of training load (measured using TRIMP) over a longer period, typically the past 42 days.
    CTL reflects your long-term fitness base. An increase in CTL generally indicates improvements in cardiovascular capacity.

  2. Acute Training Load (ATL)
    The average training load over the past 7 days.
    ATL reflects your recent training stress and fatigue.

  3. Training Stress Balance (TSB)
    Training fatigue is represented here using the Acute:Chronic Workload Ratio (ACWR):
    ACWR = ATL / CTL

How to Interpret These Metrics

Different training phases (such as maintenance or development) may use slightly different target ranges.
Below is an example based on maintenance and development phases, showing how to interpret different TSB (ACWR) ranges:

  • TSB < 0.8
    Recent training load is relatively low. The stimulus may be insufficient, making it difficult to improve fitness and increasing the likelihood of stagnation.

  • TSB between 0.8 and 1.3 (Optimal Range)
    Training and recovery are well balanced.

    • Closer to 1.3: stronger stimulus, more conducive to fitness development
    • Closer to 0.8: lighter load, more favorable for recovery
      Within this range, you can make progress while keeping injury risk low.

  • TSB between 1.3 and 1.5
    Recent training load has increased noticeably.
    Experiencing this range once or twice in a single week may help break through a plateau.
    Frequent exposure, however, can lead to accumulating fatigue and increased recovery demands.

  • TSB > 1.5
    Training load has increased too rapidly, and the body has not yet adapted.
    The risk of injury and overtraining rises significantly, and it is recommended to reduce training intensity or increase recovery.

References

  1. Gabbett, T. J., & Whiteley, R. (2017). Two Training-Load Paradoxes: Can We Work Harder and Smarter, Can Physical Preparation and Medical Be Teammates?
    International Journal of Sports Physiology and Performance, 12(Suppl 2), S250–S254.
    https://doi.org/10.1123/ijspp.2016-0321

  2. Windt, J., & Gabbett, T. J. (2019). Is it all for naught? What does mathematical coupling mean for acute:chronic workload ratios?
    British Journal of Sports Medicine, 53(16), 988–990.
    https://doi.org/10.1136/bjsports-2017-098925