I use acute to chronic workloads regularly in my clinical practice and my own personal programming. I find it to be a great tool to aid in programming, decision making, communicating progress in training, and relative risk of injury. This study is helpful in understanding the ratio and its application.
In this post I use running as the mode of exercise to demonstrate its applicability. These principles are applicable to whatever type of exercise you are programming for (resistance training, cycling, baseball pitching, etc.).
The main takeaways I have with acute to chronic workloads are this:
- Higher chronic workloads are protective against injury BUT more sensitive to sharp changes in acute workload.
- Acute to chronic ratios of 0.85-1.35 are appropriate when combined with high chronic workloads
- Acute to chronic ratios >1.5 are very risky when combined with high chronic workloads
- When starting a program without a chronic workload, the ratio is less applicable for the first few weeks.
- If you are evaluating an athlete with an injury, unless there are biological healing constraints or precautions against exercise, some level of continued training should be preferred over abstaining from exercise.
- The ratio is not only predictive of injury risk in the current week, but there is also a lag of risk for subsequent weeks.
Higher Chronic Workload is Protective Against Injury
In a previous blog post I discussed progressions in running volume.
Chronic workload can be thought of as your cash savings account. It serves as a buffer against unexpected costs and overdrafting of your “checking account”. Continuous overreaching eventually drains your savings and increases your risk of injury. A massive spike in workload also places you at risk of “bankruptcy” when it wipes out your cash reserve. So low moderate to moderate increases in workload should be preferred in programming. They are enough to elicit favorable adaptations while keeping our relative risk of injury at a more palatable level. I’ve broken down acute to chronic workload ratios into the following categories:
- <0.8 = detraining zone
- 0.8-1= deloading zone
- 1.1-1.3 = adaptation zone
- 1.3-1.5 = mild risk zone, don’t stay here for long
- >1.5 = very high risk zone, avoid this with higher chronic workloads.
How does this apply early in training plans?
If an athlete is new to a task, there is a chance that the acute to chronic workload ratio can be fairly high when initiating programming. This is because they don’t have any chronic workload so the number will be abnormally high. This may not be totally representative of a risk of injury at this time because they don’t yet have a chronic workload and they are presumably not returning from an injury. In determining starting workloads you have to be wise in your programming considering factors like training age, past experiences, and injury history. You might opt to increase workload by 10 to 20% week over week until you build.a solid 2 to 4 week chronic workload. From that point on however you should be aware of the ratio to ensure you’re not exposing the athlete to unnecessary risk.
What do you do when an athlete is injured?
Once you establish whether or not the athlete has true, biological healing constraints, or if there are precautions that necessitate they abstain from training totally you need to decide how much training is okay.
Below I present three scenarios. Let’s assume this athlete is dealing with a tendinitis or another overuse type injury and we’ve ruled out something more serious that may necessitate further diagnostics. In the first scenario, we instruct the athlete to abstain from running totally for 2 weeks. The second they will abstain from running for 4 weeks. In scenario 3, we’ll instruct the athlete to reduce, but not totally abstain from training.
Scenario 1: No Running x2 Weeks
In scenario 1, I want you to first observe what happens to their chronic workload over the following weeks. While the 4-week chronic workload doesn’t drop all that much until they start running again, their chronic workload doesn’t begin to recover until the 4th week after they begin running again. That’s 6 weeks after we instructed them to stop running. Additionally, their acute to chronic workload ratio stays >1.5 for every week until the week before their taper in week 15. That is a highly leveraged position with a lot of risk of injury or re-injury.
Scenario 2: No Running x4 Weeks
In scenario 2 we instruct the runner to abstain rom running for 4 weeks to go through a plan of care before starting training again. The problem with this is that it totally abolishes ALL chronic workload (2 and 4-week average mileage). This individual will have zero savings and will have to jump straight back into pre-injury mileages to even attempt to train before their race in week 17. Observe the 2- and 4-week ratios on their return to run. These are astronomical numbers that are simply not sustainable.
Scenario 3: Reduced Training Load x2 Weeks
In scenario 3, we instruct the athlete to drop their mileage to a maintenance level that keeps symptoms tolerable while we start a plan of care. Depending on symptom sensitivity/irritability I may instruct this athlete to drop to between 60-80% of their chronic workload. This decision is also influenced by whether or not they are actively training for a race, how much time they have before said race, and other training related factors. In this scenario, we’ve instructed the athlete to work at a 4-week acute to chronic workload of .80 for 2 weeks.
In taking a look at the table below, you can see that acute to chronic workloads are maintained at an appropriate level, risk is managed, and the impact on chronic workload is much reduced compared to scenarios 1 and 2. The athlete is able to more quickly reach pre-injury mileage and achieve a training stimulus that is favorable for their race in week 17.
Conclusions:
The key takeaways from this demonstration are as follows: Chronic workload is protective against injury. Acute to chronic workload ratios can be a useful tool to quantify relative risk in programming. It is key to determine if and what training can be continued during the evaluation and through coordination of care with the medical team. When possible, it should be preferred that some level of training is maintained to cultivate a chronic workload, lessen risk of reinjury on return to full training by moderating acute to chronic workload ratios, and to lessen time to return to performance after injury.
