What is the Acute:Chronic Workload Ratio (ACWR)?

The use of the acute:chronic workload ratio has received a growing interest in the past couple years to monitor injury risk in a variety of team sports¹. This ratio is generally computed using load over 28 days, and has been calculated using either internal (session-rate of perceived exertion) or external (tracking variables) measures of competitive and training load¹.

Acute Phase= athletes most recent workload (state of fatigue)

• Typically, between 3-7 days in duration (often recommended specific to sport competition schedule). Variance in acute phase typically based on game schedule ² ; if play once a week = 7 day compared to multiple times a week (3/4 days)².

Chronic Phase= the load the athlete has adapted to (state of fitness)

• Typically, between 3 to 6 weeks with the most recent research indicating 21 days is an appropriate chronic time window².

Why is the Acute:Chronic Workload Ratio important?

The acute:chronic workload ratio is a greater predictor of injury than either acute or chronic workload separately³.

• Compared with a low chronic workload, athletes with a high chronic workload are:
  • More resistant to injury with moderate-low to moderate high acute:chronic workload ratios.
  • Less resistant to injury with a very-high acute:chronic workload ratio.

• The acute:chronic workload ratio in the current week, subsequent week, and as an average over 2 weeks, is associated with increased injury risk in elite rugby league players ³.

Application of the ACWR

If we take a step back and dive into known research around weekly changes in workload. It’s known that increased workload results in an increased injury risk^3,4, however a lack of workload will subsequently result in athletes potentially being under prepared for game demands⁴. Therefore, finding the right balance is critical to an athlete’s success ⁴.

• Small changes in training loads between weeks has shown decreased injury (-5 to 10%)⁵
• When training loads are increased >15% injury risk varies between 21-49% ⁵

More recent research suggests analysing short term (acute) in relation to long term (chronic) load as a valid tool to measure an athletes risk of injury^3,5,6.

• The graph below is a good starting point to interpret the ACWR.
• The green shaded area is the ACWR where injury risk is low. Red indicates when injury risk is high.
• Exposing athletes to a spike in ACWR of >1.5 increases the risk of injury^3,5,7. 

The “sweet spot” ranging between 0.8 – 1.3 is the zone practitioners should aim to keep their athletes between. 

Athletes still need to be able to perform under the “worst case scenario” in game play. If they are not prepared to do so they are also at an increased injury risk⁵. It’s been shown that higher chronic loads may reduce injury risk^3,7, therefore reductions in workload may not always be the answer.

While 0.8-1.3 is a good guideline, it’s critical to also take into consideration how the athlete got there. For further detail on the ACWR and rehabilitation- Jo Clubb provides a detailed application for an athlete who suffered a groin injury, 8 week rehabilitation program and 3 weeks back into full training, a re-injury in her blog post, Acute:Chronic Workloads and Rehabilitation: A Case Study.  

How to view the Acute:Chronic Workload Ratio Chart:

1. Login to your Playertek+ account

2. Select the 'Season' Tab from the main screen 

3. Click the 'Medical Kit' Icon

4. Select Athlete from the 'Player Drop down Menu'

5. Select 'Metric' to view

6. Select 'Split' to view

7. Select Duration to view 'Week, Month or All'

8. Hover your cursor over the vertices of the line to view the Acute:Chronic Workload Ratio*

Note: Ratio is calculated using the rolling average.

*A dotted Acute:Chronic Workload Ratio line indicates that there is insufficient data in the relevant time period to calculate an accurate ratio. A minimum 21 days with regular sessions is required to achieve a full calculation. If this requirement if not met, an estimated projection will be displayed. 

References 

1. Buchheit M. Applying the acute:chronic workload ratio in elite football: worth the effort? Br J Sports Med 2017;51:1325-1327.
2. Carey DL, et al. Br J Sports Med 2016;0:1–7. doi:10.1136/bjsports-2016-096309
3. Hulin BT, Gabbett TJ, Lawson DW, et alThe acute:chronic workload ratio predicts injury: high chronic workload may decrease injury risk in elite rugby league players Br J Sports Med 2016;50:231-236.
4. Rogalski B, Dawson B, Heasman J, et al. (2013) Training and game loads and injury risk in elite Australian footballers. J Sci Med Sport; 16: 499-503.
5. Gabbett, TJ. (2016) The training-injury paradox: should athletes be training smarter and harder?Br J Sports Med; 2016;50273-280. doi;10.1136/bjsports-2015-095788
6. Blanch P & Gabbett TJ. (2015) Has the athlete trained enough to return to play safely? The acute:chronic workload ratio permits clinicians to quantify a player’s risk of subsequent injury. Br J Sports Med;0:1–5. doi:10.1136/bjsports-2015-095445
7. Hulin BT, Gabbett TJ, Blanch P, et al. (2014) Spikes in acute workload are associated with increased injury risk in elite cricket fast bowlers. Br J Sports Med; 48: 708-12.