Your Acute:Chronic Ratio (ACR) is your 1-week load (total mileage for the past 7 days) divided by your 4-week average load (one quarter of total mileage for the past 28 days).

The 'acute' (1-week) load represents your current training load. This is indicative of the stress your body is experiencing due to your short-term training. The 'chronic' (4-week) load represents your current fitness level.

There are 4 ACR zones:

• ACR between 80% and 130% (green zone): Recent sports science research (Gabbett, 2016) suggests that this is the 'sweet spot' where the risk of getting injured is low.
• ACR between 130% and 150% (orange zone): The risk of injury starts increasing when the ACR exceeds 130%.
• ACR higher than 150% (red zone): The risk of getting injured increases significantly. If your training load 'spikes' into the red zone then you may need some extra recovery time to return to the green zone.
• ACR lower than 80% (blue zone): In this zone the fitness level reduces rapidly, which could lead to undertraining and increase the risk of a future injury.

Note that these ACR threshold values are guidelines which appear to predict overtraining and the risk of injury in more than half of athletes (Blanch & Gabbett, 2015). However, while some athletes may venture in the orange or even red zone without getting hurt, others might get injured whenever they exceed 120%.

myTrainingForecast.run gives you the historic data and evidence you need to find what works for you, and which ACR thresholds you should train in.

The aerobic system adapts to training in a matter of days and you may feel that your fitness is improving very quickly. However, the connective tissues (muscles, tendons) and bones take weeks, or even months, to adapt to higher training loads. The ACR model used in myTrainingForecast.run can help you monitor your mileage to ensure you follow your actual fitness level, rather than how well you might 'feel'.

The risk of getting an overuse injury over the next 7 days can be estimated from the ACR using the methodology of Blanch & Gabbett (2015).

The injury risk shown in your forecast is based on your ACR over the past 7 days, and indicates the likelihood that you may sustain an overuse or repetitive-stress type of injury over the next days. Some of the overuse injuries that affect runners are:

• Runner's knee
• Iliotibial band (ITB) friction syndrome
• Achilles tendonitis
• Shin splints
• Stress fractures
• Muscle tears
• Plantar fasciitis

The injury risk on your training forecast does not include other types of sports injury that are caused by external factors, which cannot be predicted. These accidents are called "trauma injuries" and include, for example:

• Tripping over
• Ankle sprain

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Our algorithms and injury models are based on the latest sports science research. However, these models cannot possibly be complete and perfect. We're all made differently and a safe training load for one athlete could be dangerous for another. Regardless of what this website or anyone else says, be sensible in your training, listen to your body, and consult a medical professional if you have any concerns about your health.

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