Predicting injuries is a very difficult task because there are so many factors that contribute to an injury. One of the most common causes is due to overuse. The term “overuse” is a poor term to describe these injuries because it implies that there is a certain amount of use that is optimal. A better way to describe these injuries is to describe them as a training program error, where the workload was increased too quickly for the body to adapt to. This blog post will discuss proper training programing and also how high chronic workloads can actually be protective against injury.
Think of athletes who do ultra-marathons (generally defined as anything over 26.2 miles). Certainly these athletes would be “overusing” their muscles while doing these activities. However, injury rates between marathoners and ultra-marathoners does not vary by much. In fact, injury rates in ultra-marathoners is on the lower end compared to marathon runners (2-22% of runners compared to 19-75%). While it may be easy to attribute injuries to overall workload, it appears that it may be more complicated than that.
Using the ratio between acute and chronic workloads has been suggested as a way to predict injuries in athletes. Think of acute workloads as fatigue and chronic workloads as fitness. When the acute workload (fatigue) exceeds the chronic workload (fitness), the acute:chronic workload ratio is greater than one and the body will have to adapt to the additional stresses placed on it. If the acute workload is too great for the body to adapt to, the body will be unable to adapt to the stresses placed on it, which may lead to an injury.
Research suggests that those with a high chronic workload are better able to tolerate moderate to moderate-high acute workloads compared to those with low chronic workloads. This means that having a high chronic workload can actually be protective against injuries, as the person would have a higher level of fitness. It should also be noted that the research also found that those with high chronic workload and a very high acute:chronic workload were most likely to become injured (most likely they have exceeded their ability to adapt to those stresses).
It may seem reasonable to keep chronic training workloads low in an effort to decrease the risk of injury, however, this becomes problematic if your sport requires higher workloads. This would cause a spike in training workloads during competition, which would increase the risk of injury. Therefore, maintaining a similar chronic workload with acute workload is a better strategy to decrease injury risk.
One way to estimate your workload would be to estimate the exercise intensity on a scale of 1 to 10, then multiply that by the duration of activity. For example, a run that was rated a 5 intensity for 60 minutes would be a 300 unit workload. Another example would be a 20 minute weight lifting session that was rated a 8 in intensity would be a 160 unit workload.
When using the acute:chronic workload ratio, the “sweet spot” seems to be between 0.8 and 1.3. This amount of stress stimulates the system enough to cause adaptation but limits the risk of injury. In the example above, let’s say that the runner went on a 60 minute hill run that was an 8 intensity. The acute workload would be 480 units (8*60 = 480), which would be a 1.6 acute:chronic workload ration (480/300 = 1.6)… putting them at a greater risk of injury.
If our runner was injured during their hill run, usually we would say that they suffered from an “overuse” injury. However, they actually suffered from a training error by exceeding their current training level. The point being that the runner would be able to do the hill run without overusing anything, they just need to increase their chronic workload (fitness) before attempting it.
While preventing all injuries is impossible, it is possible to reduce your risk of injuries through smart training. Try keeping a journal with your normal workout routine to estimate your chronic workload amount over 2-3 weeks. Then you can plan your training progression for acute workloads accordingly to stay within the 0.8-1.6 acute:chronic ratio. Happy training!
Hulin, Billy T., Tim J. Gabbett, Daniel W. Lawson, Peter Caputi, and John A. Sampson. "The Acute:chronic Workload Ratio Predicts Injury: High Chronic Workload May Decrease Injury Risk in Elite Rugby League Players." British Journal of Sports Medicine Br J Sports Med (2015)