So what exactly does Swiss cheese have to do with injury risk? Well, we’ll get to that… I first became aware of the so-called Swiss Cheese Model during the COVID-19 pandemic. Given its permeable structure, Swiss cheese has been used as an analogy for reducing risk. First, we’ll explore how it was used in relation to the Coronavirus pandemic before reframing it within the context of injury.
The Swiss Cheese Model
The concept was introduced by cognitive psychologist James T. Reason in 1990 in relation to accidents. He published the “Swiss cheese model of accidents” in the book Human Error, as an illustration of compounding errors that can lead to catastrophes, such as the Chernobyl disaster and the Challenger shuttle explosion. Reason acknowledged that no single intervention is flawless for preventing accidents and therefore, a multi-layered approach should be used.
During Covid-19, the Swiss cheese model surfaced in numerous conversations relating to interventions in response to the pandemic. Dr Mackay, a virologist at the University of Brisbane, shaped this concept into the “Swiss Cheese Respiratory Pandemic Defence” with collaborators and feedback via Twitter. Thanks to the think tank of social media, it developed over a number of iterations, with version 3.0 shown below (although having just checked, it now seems to be up to v4.2!).
Why Swiss Cheese?
In a New York Times article, Dr Mackay describes the interaction of different layers of intervention, represented by the cheese slices:
“…it’s not really about any single layer of protection or the order of them, but about the additive success of using multiple layers, or cheese slices. Each slice has holes or failings, and those holes can change in number and size and location, depending on how we behave in response to each intervention.”
The holes in Swiss cheese illustrate that no single layer of intervention is flawless. Multiple layers of interventions can assist in reducing risk of failure; be it, the spread of a virus or the risk of injury.
Other features of Dr Mackay’s model include the distinction between personal and shared responsibilities, and the “misinformation mouse” that can erode the effectiveness of these interventions by taking bites out of the cheese slices! So let’s consider this model and its features in relation to injury.
Let’s Talk Injury!
We have previously discussed the benefits of learning from outside domains. Using lateral thinking, we can apply the Swiss Cheese Pandemic Defence to injury risk reduction.
This concept provides a cognitive framework for thinking about injury risk reduction; a way of considering the different layers of interventions we have in place and the mixed responsibility associated with them. It can also serve as a reminder that when injury occurs, it is likely not due to a single risk factor, such as training load or strength of a particular muscle group, but the result of an inciting event that permeates multiple layers of risk.
In the figure below, I have replaced the COVID-19 interventions with a selection of injury risk reduction strategies. While this is not designed to be exhaustive, it demonstrates the variety of strategies we have within our arsenal to try to reduce the risk of injury.
The model also highlights the mixed responsibility involved with trying to reduce injury risk. Professional habits and honest medical reporting, for example, are clearly the obligation of the individual athlete. Meanwhile, other interventions extend across multiple stakeholders, not just to the coaches and performance staff (such as planning the schedule and training load), but to the broader sporting association that decide on rules and regulations pertaining to injury risk. This framework can also highlight the effectiveness of an intervention is not necessarily dichotomous. How well the intervention is implemented can determine the frequency and size of the holes in the layer. In the case of COVID-19, the effectiveness of a mask can be limited by how it is worn, how well it fits, the type of material, as well as the wearer’s behaviour relating to washing their hands and the mask itself frequently. Similarly, there is a wide spectrum in how well a particular warm-up can reduce the risk of injury, depending on how well designed, coached, and executed it is.
Mackay has spoken with the NY Times about the ability of the misinformation mouse to erode the Swiss cheese layers, stating; “people who are uncertain about an intervention may be swayed by a loud and confident-sounding voice proclaiming that a particular layer is ineffective.” Misinformation is an issue in our field too of course, but I’d also like to link this into the potential for belief effects too.
Performance improvements are observed in athletes that believe in a novel and exciting performance-enhancing intervention, regardless of real treatment effects (Halson and Martin, 2013). Perhaps then, the athlete’s expectation of a particular intervention may strengthen, or erode, that particular layer of Swiss cheese.
Of course, reducing injury risk is not as straightforward and linear as perhaps this figure may suggest. There are three key aspects of injury risk – previously discussed in our “Understanding the Evolution of Injury Aetiology Models” – that I wish to highlight in relation to this framework:
Individualised – injury risk is individualised and therefore, the Swiss cheese model, including the layers and holes, would look different for everyone.
Recursive – injury risk is not a single linear process but a continuous loop with each repeat participation exposing the individual to risk. Therefore, the individual is cycling through the layers of intervention with every athletic exposure.
Dynamic – injury risk is constantly changing and therefore, so are the size and alignment of the holes. Reason also acknowledged this in relation to accidents, stating: “though unlike in the cheese, these holes are continually opening, shutting, and shifting their location.”
Final Thoughts
Injury is complex. A cartoon of Swiss cheese cannot prevent injuries. But, it can serve to act as a cognitive framework to think about the layers of interventions we have in place. It highlights the mixture of personal responsibilities on the individual athlete and those responsibilities shared across the wider sporting community; from teammates and support staff, to researchers and policy makers.
The model also highlights that sometimes risk can permeate our defenses and cause injury; despite the multitude of strategies we have in place. As we seek to understand more and more about injury, we strive to learn what different layers of Swiss cheese look like for different athletes and the dynamic and individualised nature of their injury risk.