Acute VS Chronic Workload
Welcome back. I assume that if you’re reading part deux that you are somewhat interested in the topic of preventative training measures. And as promised, I’m going to outline some more objective measures for calculating this ACWR concept. We are going as basic as possible so that everyone can try it regardless of training background. Be prepared for a read, but it is straightforward.
In Part 1, I introduced the idea of the ACWR and why we should give it credence. Ideally, it will give you an idea about your own readiness or an athlete’s preparedness. Again, a quick review is that it compares an individual’s fitness to their fatigue to understand their relative risk of injury, or also their readiness to perform. We want to look at “what has been done” and how that prepares us for “what we are about to do.”
Typically we will look at a month, or four weeks. There are a number of different models that can be used to calculate your ACWR, but for purposes of this post to be as educational as possible, I will outline a basic framework to use. Again, I there are multiple ways of calculating and there are sliding scales for fatigue, however I want to keep it simple for this post. For this, we will use four weeks and something know as the Rate of Perceived Exertion (RPE) scale. There are also two forms of RPE, but we will again use only one, despite both being accurate. Our RPE scale for this discussion is a progressive scale representing your own perceived level of effort or work. It ranges from 0-10 or rest to maximal effort respectively. 0 represents the easiest effort exerted and 10 represents maximal all out effort/fatigue. There are other values in between which represent various levels of effort. I encourage you to look them up to become familiar with how to rate your own effort.
If you remember, I described someone’s chronic workload as the fitness gained from the previous few weeks of training. Conversely, the acute workload is the fatigue felt from the current week’s training. This holds true regardless of the discipline or sport. Which is why we will use RPE.
To apply RPE and gain an objective value to be used to calculate cleanly, we use something called Arbitrary Units (AU). They are just that, arbitrary, but they give us a relatable objective measure from a relatively subjective (RPE) concept. And the way we calculate AUs is by taking the RPE of each session and multiply it by the total number of minutes in that training session. So for instance, if you trained for 100 minutes and you feel that by the end of that session your RPE effort is a 5, then your AU for that session is 500 (100×5=500). Or if you had a very hard 45 minute session and your RPE at the end was an 8 then your AU is 360. You can see here how the number can creep up the harder the effort. This is why I truly appreciate this concept to rate the preparedness of my athletes and gauge potential risk of injury. So now lets take this a step farther.
How do we calculate a week? We take the average AU for that week’s total workouts. Add up each individual AU and then divide by 7. This gives us the weekly AU value. At the end of the month, you take each weeks chronic workload AU and divide by 4 (weeks) and this gives you your chronic workload value. The following example is from scienceforsport.com. They also have a phenomenal writeup that can get technical at times. But still extremely helpful.
Week 1 = 1400 AU average
Week 2 = 1200 AU average
Week 3 = 1800 AU average
Week 4 = 1600 AU average
So the chronic workload for these four weeks would be 1500 AU. That is the average (6000/4) given the self-reported AU based on our 0-10 RPE scale. This represents your fitness.
Now that we have the chronic workload value, we need to calculate the acute workload value. This represents your fatigue. Calculate the AU for the week you just recently finished. Then, divide that acute AU by the chronic. We want that ratio value to be less than 1.0 ideally.
To take that example above just a step farther:
Week 5 = 1200 AU avg
Weeks 1-4 represent chronic and their avg AU is 1500
Week 5 represents acute and its avg is 1200.
We divide the acute value by the chronic previous 4 week’s value.
1200 / 1500 = .80 ACWR. This value is below 1.0 and is a green light, less risk of injury if training volume growth stays the same.
On the other hand, if the chronic workload was higher lets say:
Week 5 AU = 1800
Then the ACWR would be greater than 1.0 (1800 / 1500 = 1.2). And thus, risk of injury would go up because the current amount of training volume or stress on the body is greater than what your body has experienced over the past few weeks and consequently has not been able to prepare well enough for the new physical stress.
Think of it this way, if you play a sport and are practicing for the championship game, you have to imagine the practice season represents your chronic workload and the championship game represents the acute workload. If your opponent in the final game is much stronger than any of the practice partners, then you are not setting yourself up for success in the final game. You will not be able to rise to the demands of the final game. If, however, you made sure that your practice partners were very difficult to match the same intensity or greater than that of your final match opponent, then you are setting yourself up for success in the end. The stress or effort experienced during that final game is not unfamiliar. You are prepared well-enough to handle the rigors of that final game.
This same process is used regardless of the sport, because we are keeping it basic and we are using RPE. The key there being “perceived.” If you are sick, or didn’t eat well, or didn’t sleep well then a relatively simple workout can take a great toll on your body and your RPE for that workout may be higher even though it has been a simple workout in the past. We have all experienced those times when you’re tired and simply walking up the stairs seems like a chore. Well guess what? Your RPE for that brief bout of physical effort is much higher than it normally would be. Could be a 6 when its usually a 2. This is why I love RPE and this concept.
Our goal is to always keep the ACWR below 1.0 in order to minimize risk of injury. I do recognize that there are many of variables at play, but this concept is an important one to understand. Please don’t take this as the final say in how well-prepared you will be. As always, there are a number of things at play. This concept is meant to help you structure your training load/volume. My number one goal as a healthcare provider is to help people mitigate risk of injury in order to maximize potential performance.
Thanks for reading, and I understand it is a textual representation of a somewhat complicated topic. I hope to have done my best to break it down, but as always, please don’t hesitate to reach out with any questions, comments, concerns, or grammatical errors I may have committed. For that I apologize =)