In our last article we looked at the dramatic effects of detraining – missing training through injury, illness, holiday, or choice – and how long it takes to get that level of fitness back. The take home message was finding any form of exercise that maintains some conditioning during “down times” can dramatically reduce the amount of time needed to return to top condition!
Now we’re going to look at a related topic: preventable injuries that occur due to a spike in training loads. A spike in training loads can happen in a few ways
– After a layoff as mentioned above, and returning to sport/activity and trying to complete a session that is too difficult relative to the amount of time you have had off. This is classic – have a holiday, feel well rested, and come back into a heavy training session!
– Adding a significant chunk to an existing training program. In this case, even fit and conditioned people can be prone to injury through training error: simply adding too much load too quickly.
So we’ll look at a neat way to monitor these loads and hopefully help reduce training errors and injuries.
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We live in a world full of technology and it’s simply amazing the data any person can now gain from gadgets such as a wrist watch: steps, cadence, heart rate, calories burned, distance travelled and the list goes on. All of this simple data can be interesting relative to the current training session you are doing, but don’t necessarily help with accumulative training loads over time.
At semi elite and elite levels of sport, GPS tracking devices are used extensively to monitor data such as total distance travelled, speeds reached, sprint distances, game time played and all these recordings can be plugged into software that calculates total loads at a single click. But how about for us average people who don’t have this luxury? Well, there’s a way you can easily keep an eye on training loads and keep yourself out of the high risk injury zone!
Acute Chronic Workload Ratio (ACWR)
Something that has been studied quite extensively in professional sport is the concept of ACWR – within this concept, Acute Workload is the amount of training/exercise you have completed in the most recent 7 day period; Chronic Workload is the amount of training/exercise you have completed in the four weeks immediately preceding the most recent week. Put simply, over a 5 week training block, weeks 1-4 formulate your chronic workload and the 5th week is the acute workload figure.
Without the advantage of GPS tracking systems, we can use a neat and easy system to generate our own ACWR, and we do this by recording the workload of each session we complete by multiplying the duration of each session (in minutes) by the Rate of Perceived Exertion (a figure out of 10 that correlates to our perceived effort/intensity of that session).
For example, if I have just ridden a bike for 60 minutes and worked extremely hard (close to maximum effort) over that time, I might rate my RPE as 9/10. My training load would therefore be 60 x 9 = 540 units. If I trained exactly the same four times over the week (which I know is unlikely), my 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 I have 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
My chronic workload is calculated as the average of 720 + 940 + 1020 + 1500 = 1045 units
Now…my ACWR is 2160/1045 = 2.06
OK so we now know our ACWR, but what does it mean?
Researchers have found that there is an ACWR “sweet spot” of between 0.8 – 1.3, and within this sweet spot your risk of soft tissue injuries is at its lowest. Check out the following table for ACWR levels and injury risks:
• ACWR 0.8 = 5-7%
• ACWR 0.8 – 1.3 = 5%
• ACWR 1.3 – 1.75 = 7-10%
• ACWR 1.75 – 2.0 = 10%
• ACWR >2.0 = 15%-20%
An interesting fact to note is that the resultant injury (from an incorrect ACWR) may not occur for up to 4 weeks after the overloaded training week, and that is why we don’t often correlate that training week as a cause of the injury! This risk periods differs between sports: in rugby, the riskiest time is 7–10 days after the training spike whereas in cricket fast bowlers the injury risk is 21–28 days post spike.
So you can see how a fast bowler at cricket may be at risk following an extensive bowling session on a Saturday. But the great news is, you don’t necessarily have to keep that bowler to less overs during that particular game: remember the injury occurs 3-4 weeks after the overload. But by tracking the ACWR, we can “flag” a spike in load during that particular game/week, and just ensure that the following 2-3 weeks are reduced in intensity and time to get the rolling 4 week ACWR back into the “sweet spot”.
Special mention here to our colleague Mick Hughes for the following Christmas time example, which is a classic one highlighting the risks of the festive season for athletes:
Week 1 (before Christmas break) = 1500 units
Week 2 (holiday) = 0 units
Week 3 (holiday) = 0 units
Week 4 (after Christmas break) = 1500 units
Week 5 you decide to increase your training by 10% from the preceding week (which on the surface would seem sensible) = 1650 units
Here’s the calculations:
Acute Workload = 1650 units
Chronic Workload = 750 units (1500 + 0 + 0 + 1500/4)
ACWR = 2.2… and danger!
You really wouldn’t think that taking a short, complete break could have such an impact on injury risk, but it certainly does. And this ties in well with our previous blog of the effects of detraining – even maintaining some form of exercise will dramatically reduce your injury risk, and allow you to pick up training again a lot easier!
Make sense? The main take home messages are:
– Poor training (under or over training) has a definite injury risk.
– ACWR is an easy way to track your training schedule, and plan your future sessions.
– There is a sweet spot within the ACWR that should be maintained as best as possible.
– If you have an outlier week of training (under or over), there’s no need to stress – you just need to make sure your next 2-3 weeks of training bring you back into the sweet spot!
You really wouldn’t think that taking a short, complete break could have such an impact on injury risk, but it certainly does (as does having a massive spike in training). And this ties in well with our previous blog of the effects of detraining – simply maintaining some form of exercise during holiday or injury periods will dramatically reduce your injury risk, and allow you to pick up training again a lot easier!
Anthony Lance
SSPC Physiotherapist
References available on request
