In a previous blog post, I discussed how pain during exercise can be used as a guide to keep from ‘overdoing it’ and injuring yourself. But what if you don’t have any pain? Well, that’s a great situation to be in, but sadly it is still all too easy to suffer injury from doing too much, too quickly. That is why I am excited about some new research that suggests a simple way to measure your activity level to help avoid overuse injuries!

This new metric is called the “acute:chronic workload ratio”, and it comes to us from the Australian sports scientist, Dr. Tim Gabbett, and his colleagues^1-5. The basic idea is to compare your short-term (previous week) workload against your longer-term (previous month) workload. (The previous week’s workload is called the ‘acute’ workload, and the previous month’s workload is called the ‘chronic workload’.) If you’ve been exercising the same amount every week, then this ratio will be 1. If you’ve been ramping up over time, then the ratio will be greater than one, and it will be less than one if you are ramping down.

To see how the ratio works in real life see this example below for a runner:

Acute Workload: 50 miles running the previous week

Chronic Workload: 300 miles running the previous 4 weeks   =   75miles/week average

Acute:Chronic workload ratio

50:75

50/75 = 2/3

Is 2/3 a good result? This is a good question and one that Gabbett and colleagues studied. To date, they have studied three sports, which have different physical pressures: cricket fast bowlers², Australian rules football³, and rugby league^4-5. They found that moderate-to-high ratios increased injury risk. They found that high chronic workloads reduced injury risk as long as the acute loads were proportionate. In other words, they found that high exercise levels reduce injury risk as long as the ramp-up to the high level is gradual enough, and the workload is consistently maintained. Therefore, a high chronic workload is a preferable long-term goal for injury prevention as long as it is reached gradually.

The “sweet spot” indicated by the research so far is between 0.8 to 1.3, as shown in the figure below. When the ratio exceeds 1.5, injury risk in increased 2-4 times in the following week. Allowing the ratio to drop too low also increases injury risk compared to staying in the ‘sweet spot’, but the risk is still much less than when the ratio spikes high.

A visual representation of the acute:chronic workload ratio, adapted from Gabbett et al.

The figure above really highlights how training has to be a gradual progression. The acute:chronic workload ratio can be a useful tool (along with pain monitoring) for athletes and coaches to pace workload progression. I think it can be particularly useful to an athlete if they are considering making changes to their plans, or are going to work with a new coach. If the new coach recommends a training schedule where the new (acute) workload is too great relative to the old (chronic) workload the athlete can express concern and discuss. I am also excited to start using this metric in my practice to better understand whether an athlete’s injury might be related to recent overuse or workload changes.

As always, using these methods does not guarantee injury-free sports performance. . A limitation of this work is that so far it has only been studied in three sports. However, two of the sports, Rugby League and Aussie rules football, include a lot of running and have a lot of similarities with other sports (i.e. soccer, football etc.) Therefore, I expect the results to be replicated in different areas, and in time we should see more sports medicine professionals and coaches making use of this metric.

June 2016 update: see how the acute:chronic workload ratio influences taper in this new blog post!

May 2018 Updated: Hear Andrew talk about the ACWR on video on Facebook.

References:

1. Gabbett TJ. The training-injury prevention paradox: should athletes be training smarter and harder?. Br J Sports Med. 2016;50(5):273-80.
2. Hulin BT, Gabbett TJ, Blanch P, Chapman P, Bailey D, Orchard JW. Spikes in acute workload are associated with increased injury risk in elite cricket fast bowlers. Br J Sports Med. 2014;48(8):708-12.
3. Blanch P, Gabbett TJ. 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. 2015;
4. Hulin BT, Gabbett TJ, Caputi P, Lawson DW, Sampson JA. Low chronic workload and the acute:chronic workload ratio are more predictive of injury than between-match recovery time: a two-season prospective cohort study in elite rugby league players. Br J Sports Med. 2016;
5. Hulin BT, Gabbett TJ, Lawson DW, Caputi P, Sampson JA. The acute:chronic workload ratio predicts injury: high chronic workload may decrease injury risk in elite rugby league players. Br J Sports Med. 2016;50(4):231-6.