One of the key components discussed in our recent podcast on Load Management was the concept of “Acute: Chronic Workload Ratio’s” (if you missed the podcast check the link at the end). This basic ratio forms a topic in its own right, so I thought I’d expand on that in this month’s article.

We have looked quite extensively in recent articles, and in the podcast, at the dramatic effects of undertraining – be that due to an enforced rest like injury time out, a chosen rest such as a holiday or “freshen up” sabbatical, or unfortunately due to training error such as trying to manage loads safely but ending up undertraining. In an absolute irony, we find that the many athletes who are trying to avoid injury by monitoring their loads, are actually increasing their injury risk by being too safe. And not only is there an increased injury risk, but put simply: if you aren’t training hard (and consistently hard) then you just aren’t going to be able to perform near your maximum potential.

One great way to start monitoring what training load you are doing is to understand Acute Chronic Workload Ratio’s (ACWR). We live in a world full of technology and gadgets, so getting training data is actually quite easy. You can track data such as steps, cadence, heart rate, calories burned, distance travelled and the list goes on. But 10,000m or 15,000 steps, or a HR of 130 is not really helpful at all, unless is relative to a baseline or some other figure for comparison.

What is Acute Chronic Workload Ratio (ACWR)?

The concept of ACWR has been studied quite extensively in professional and semi professional sport, and it is this ratio that gives us a simple and reliable baseline from which we can compare and utilise the data we have gained from our most recent training session. To be able to calculate the ratio (which is actually quite simple) you need to understand what Acute Training Load is, and what Chronic Training Load is!

Acute Workload is the amount of training/exercise you have completed in a recent time period. The most commonly used acute timeframe for most people is the most recent 7 day period but this time period can be adjusted according to your training frequency – if you are a swimmer, swimming 2 sessions a day, then your acute period should probably be shorter, let’s say 4-5 days, due to the amount of sessions you are monitoring and recording.

Chronic Workload is the amount of training/exercise you have completed over a longer time period, immediately preceding your acute time frame. Again, for most people this chronic time period will be four weeks. In the case of the swimmer above, if using a 5 day acute time frame, the chronic time frame may be 3 weeks. For the purposes of this article, we will take one week of training as the acute time frame, and four weeks as the chronic time frame.

Using these time frames, you will need five weeks of training data to be able to calculate your ratio: the most recent week (acute workload) and the four weeks immediately preceding that week (chronic workload).

Hopefully that makes sense, but what do you record as your training data. Most of us don’t have the luxury of wonderful software programs to automatically calculate GPS data into a nice ratio – but you don’t need advanced software or megabytes of GPS data to get some really useful information.

To be able to track your training (and your ACWR), we use two simple factors:

  1. Firstly, you do need some objective data! If you have a fitbit, a Garmin, a smartphone or watch, google maps etc, you will get what you need. If you run, you might track distance or time; if you swim, you will probably track laps or time; if you’re a cricket bowler you might tracks balls bowled. One simple parameter that reflects your training/sport is all you need.
  2. Secondly, we use Rate of Perceived Exertion (RPE). And this is really important because a 10km run is very different to an elite ultra-distance athlete compared to a social twice a week runner. RPE uses a scale of 1 – 10 (where 1 equals the easiest training session you could have completed, and 10 is a near death experience!).

RPE puts some relativity into training sessions: for the ultra-distance runner who normally goes for a 38km run, this 10km run might be graded as a 1; for the recreational twice a week 6km runner, the rating might be an 8; for the dancer who has been told to increase their aerobic fitness and go for a run, the rating might be a 10. This rating is so important because it puts emphasis on how hard that training session has been for you! And if you have too many hard training sessions in a period (or too many low training sessions) your injury risk is increased!

Let’s use the example of a cyclist who has just ridden his/her bike for 60 minutes, working extremely hard (close to maximum effort) over that time, and rating the session as an RPE of 9/10. This person’s training load would therefore be 60 x 9 = 540 units. If this person trained exactly the same, four times over the week (which I know is unlikely), their ACUTE Workload would be 4 x 540 = 2160 units.

Let’s say for the purpose of this example that in the preceding 4 week period the cyclist has completed:

Week 1: 3 rides x 40 minutes x 6/10RPE. Workload = 720 units (3 x 40 x 6)
Week 2: 2 rides x 45 minutes x 6/10 RPE; 1 ride x 50mins x 8/10; Workload = 940 units
Week 3: 1 ride x 60 minutes x 8/10RPE, 2 rides x 45 minutes x 6/10RPE. Workload = 1020 units
Week 4: 2 rides x 60 minutes x 8/1-RPE, 1 ride x 60 minutes x 9/10RPE. Workload = 1500 units

The cyclist’s chronic workload is calculated as the average of 720 + 940 + 1020 + 1500 = 1045 units

Now…the ACWR is 2160/1045 = 2.06

OK so we now know the ACWR, but what does it mean? Take a look at the graph below which comes from noted Sports Scientist Tim Gabbett:

Researchers have found that there is an ACWR “sweet spot” of between 0.8 – 1.3 (green on the above graph), and within this sweet spot your risk of soft tissue injuries is at its lowest. Above a level of 2, injury risk becomes quite high.

Using data from the graph above, or more importantly from your own data, the following points apply:

  • Lowest or highest injury risk doesn’t mean you won’t or will get injured. In fact the strong argument is that if you are constantly training in and around your “sweetspot” you will probably have a higher injury risk when the inevitable spike in load (big training session or intensive game/competition) comes along. Knowing risk just helps you plan your next session.
  • Undertraining AND overtraining have injury risk.
  • Utilise the data to know when you have had a spike in acute load. Spikes are important to get fitter, stronger, faster etc.
  • At times, periods of hard training are important and necessary. You will tolerate higher training loads (acute load) better IF you have a high training base (chronic workload).
  • By tracking the ACWR, you can “flag” a spike in load during that particular game/week, and just ensure that the next acute load period gets somewhere back to near (not necessarily within) the rolling 4 week ACWR (the “sweet spot”).
  • Your chronic load really reflects your state of fitness, and the acute load reflects your level of fatigue (or lack of). If your acute load is lower than your chronic load, you are in a state of fitness; if your acute load is higher than your chronic load you are in a state of fatigue.
  • Don’t avoid the red zone at all costs. Just realise when you have been in the red zone, and adjust accordingly – options might be: make sure your next session is in the sweetspot; put more attention to recovery that week; make sure you get some quality sleep during that time. Red isn’t necessarily a problem, unless you are constantly in the red, and especially if you are constantly spiking loads from a low training base.
  • Any resultant injury (from poor training loads) may not occur for up to 1 – 4 weeks after the overloaded training week, and that is why you won’t often correlate that big training week/session as a cause of your injury!

If I could summarise all this into one statement, it would go like this:

Training harder is training smarter. But to train harder you need some form of tracking system to ensure you don’t go overboard for too long, or too quickly. To be more resilient and robust against injury, AND to be performing at or near your maximum levels, you need high loads and intensive training sessions, but you must be able to track this to know when to back off a fraction and put some more emphasis on the important components that make up recovery! Develop a system to ensure you get to high chronic loads (fitness) but do it systematically and safely!

Anthony Lance
SSPC Physiotherapist

PerformPreventRecover podcast: Load Management

References available on request