Sports Injuries Are Linear.. Or Are They?

Sports Med U | Educating Minds, Elevating Potential

Complex systems approach for sports injuries: moving from risk factor identification to injury pattern recognition—narrative review and new concept

Bittencourt, N.F., Meeuwisse, W.H., Mendonça, L.D., Nettel-Aguirre, A., Ocarino, J.M. and Fonseca, S.T., 2016. Complex systems approach for sports injuries: moving from risk factor identification to injury pattern recognition—narrative review and new concept. British journal of sports medicine, 50(21), pp.1309-1314.

In today’s letter

• Overview of the of the “complex” system approach and tips on how to look at injuries from a different perspective

• 3 clinical tips

• A fun infographic for you to save and use in the future

• 3 resources to check out to further your knowledge about …

• Meme of the week: My poor Little back 😅 

• Rapid Results =

Sports injuries come from complex, non-linear interactions within the body, which makes traditional reductionist approaches faulty. Adopting a systems-based approach helps identify patterns of risk and allows for more effective injury prevention and rehab.

• Professional takeaway =

When evaluating an injury, consider the broader system of interconnected factors such as training load, recovery, biomechanics, and mental state, rather than isolating a single risk factor. For example, restricted ankle dorsiflexion combined with high training load may increase patellar tendon stress, so addressing both mobility and load management is important.

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Tendinopathy specific guides with diagnosis, management & differential diagnosis you should know about.

Aim of the study

The goal of this paper is to introduce a new way of thinking about sports injuries using a complex systems model, showing how this approach can help us better understand and tackle the complicated nature of why injuries happen

Sports Injuries Are More Like Spider Webs Than Dominoes

Predicting and preventing sports injuries with the old-school approach has a big problem: it’s too simple for such a complicated reality.

Traditional methods treat injuries like a game of dominoes — one thing knocks over another in a straight line. But in reality, sports injuries act more like a spider web — tug on one part, and the whole thing shifts.

So, why does this matter?

Because if we want to get better at keeping athletes healthy — whether they’re weekend warriors or pros — we need a new way of thinking. That’s where the complex systems approach comes in.

Why Traditional Models Fall Short

Old-school injury prediction models look for isolated risk factors, like tight hamstrings or a history of ankle sprains. They assume a direct, linear relationship: X causes Y.

But sports injuries rarely follow such a neat script.

Consider this:

• Non-linear relationships: A small change in one factor (like fatigue) can lead to a huge increase in injury risk, but only when combined with other factors (like poor recovery).

• Interconnectedness: Training load, biomechanics, mental state, and sleep interact in ways we’re just starting to understand.

• Changing susceptibility: An athlete’s injury risk isn’t static — it evolves based on their environment, stress, training, and recovery.

What’s a Complex System Approach?

Imagine trying to predict the weather.

Yeah, looking just at the temperature will do the job if your just going for a stroll in the park.

But what about if you’re thinking of climbing a mountain with peaks and vallys’s?

You need to consider humidity, wind patterns, pressure systems, and how they all interact. Sports injuries work the same way.

The complex systems approach helps us:

• Identify how different factors combine to create injury risk.

• Understand the “emergence” of injuries — how they arise from a network of interactions.

• Adapt injury prevention and rehab strategies as athletes change over time

The Old Way: Reductionism

This method breaks down problems into individual parts and looks for simple cause-and-effect relationships. It’s worked well in some cases — like linking smoking to lung cancer.

In sports, we’ve seen it with things like dynamic knee valgus (DKV) — when the knee caves inward during landing — being connected to ACL injuries. Studies show female athletes with DKV are five times more likely to tear their ACLs.

However, reductionism only captures part of the picture. It assumes injuries happen in a neat, linear way — one event directly leading to another — and that’s rarely how the body works.

The New Way: Complexity

The complex systems approach acknowledges that injuries often arise from a mix of factors interacting over time. Let’s take patellar tendinopathy as an example.

Two risk factors:

• Restricted ankle dorsiflexion (limited ankle mobility)

• High training load (intense or frequent training)

Neither of these alone guarantees injury. But together, they create a good environment of tendon overload.

Limited ankle mobility changes how forces are distributed in the leg, and when combined with high training load — the patellar tendon takes on too much stress.

This interconnectedness is what the complex systems approach helps us see. It shifts the focus from isolated risk factors to patterns of interaction, helping us better predict and prevent injuries.

Why Sports Injuries Are More Complicated Than You Think

Let’s take a basketball team as an example. Each player has their own skills, but the way they play changes depending on their teammates’ movements. The same goes for your body. Different parts — biomechanical, physiological, psychological, and behavioral — constantly interact, and those interactions shape how your body responds to stress and movement.

The characteristics of a complex system:

• Interconnectedness: Parts of the body don’t work in isolation. Knee behaviour changes based on ankle’s position, core stability, and the mental state.

• Non-linearity: Small changes can lead to big results — or none at all. Tight hips might cause lower back pain in one athlete but no issues in another.

• Self-organisation: Your body adapts and organises itself in response to training, fatigue, and injury — often in ways we can’t fully predict.

• Emergent properties: The whole is greater than the sum of its parts. The way the persons runs or jumps is about how all muscle work together, not how they work individually.

• Open system: Your body constantly exchanges energy and information with the environment. Think of hydration, nutrition, and emotional state — they all affect performance and injury risk.

This type of behaviour is frequently seen in sports injuries, where different relationships among risk factors can produce the same injury (known as an emergent outcome). Because the body is an open system that evolves over time, there are often multiple pathways to similar results.

• Inherent non-linearity: Complex systems don’t follow a simple cause-and-effect pattern. In a linear system, the output is directly proportional to the sum of its parts. But with non-linear systems — like the human body — a small tweak can lead to major changes, while big changes might have little to no effect. For example, a knee valgus is often linked to hip abductor weakness. But even strong hip abductors might not prevent the cave in if there’s high hip internal rotation stiffness. This non-linear relationship shows why injury prediction is rarely straightforward.

• Recursive loops (Feedback): Complex systems often feature feedback loops, where outputs influence future inputs. Take the interaction between the hypothalamus, pituitary gland, and ovaries. Hormones released by one part affect the next, and those responses cycle back to regulate the original input. In sports injuries, feedback loops mean that once an injury occurs, the system adapts in unpredictable ways, making previous risk factors less reliable.

• Self-organisation and emerging patterns: Through self-organisation, individual parts of the system cooperate to create new, sometimes unexpected patterns. These emergent properties can’t be predicted by looking at individual parts alone. In sports, this can lead to recurring injury risk or protective profiles — patterns that show up consistently despite the complexity of their causes.

• Uncertainty: To predict injuries its importnat to recognise patterns and probabilities. Despite the unpredictability of individual outcomes, identifying consistent patterns helps reduce uncertainty.

Why does this matter for injury prevention and rehab?

Because a tweak in one area — like strengthening glutes — can improve knee alignment and prevent ankle sprains. It also explains why two people with identical injuries might heal at different rates.

Solving the Injury Puzzle

ACL Injuries in Basketball vs. Ballet

Let’s take ACL injuries — a common and serious knee injury — and see how different sports create different risk patterns.

Basketball Players:

• Main Risk Factors: Poor knee valgus, weak hip muscles, and unexpected environmental events (like an opponent’s sudden movement)

• Influences: Fatigue, neuromuscular control, training load, and psychological elements like anxiety

• Outcome: When enough of these factors pile up and an unexpected event happens, the risk of injury skyrockets

Ballet Dancers:

• Main Risk Factors: Fatigue, attention level, anxiety, and movement quality

• Influences: Training volume, psychological stress, and sex differences

• Outcome: Fatigue impacts movement quality, and that can lead to knee issues and ACL injury

Notice how the same injury comes from different risk patterns in different sports?

What This Means for Injury Prevention

If we want to prevent injuries, we can’t just focus on one thing like muscle strength or stretching. We need to look at the entire web of factors and how they interact. That’s why comprehensive training programs that address physical conditioning, mental resilience, and load management are so important.

A Mental Model for Injury Prevention

Here’s a simple framework to help you think like a complex systems pro:

1. Think Interactions, Not Isolations: Look at how factors like fatigue, strength, and stress influence each other.

2. Track Patterns: Keep a journal to spot recurring combinations that might lead to injury.

3. Adapt: Adjust the training and recovery based on the bigger picture, not just one factor.

Clinical Tips

1. Think Different

• Move beyond isolated risk factors (e.g., tight hamstrings or weak hips) and consider the whole picture (e.g., training load, sleep, stress, biomechanics, and mental state).

2. Look for Non-Linear Relationships in Injury Risk

• Recognise that small changes in one factor (e.g., fatigue or poor recovery) can lead to disproportionate increases in injury risk when combined with other factors. For instance, a slight increase in training intensity might not cause issues alone, but when paired with inadequate sleep, it could significantly elevate injury risk. Monitor these interactions closely.

3. Track Patterns Over Time

• Encourage athletes to keep a detailed journal tracking training load, recovery, sleep, stress, and performance. Look for recurring patterns that may indicate emerging injury risks.

Top 3 Resources to Check Out

And learn more about sports injuries

1. Different types of injuries (PDF) - LINK

2. Injury Prevention (Book) - LINK

3. Defining injury in sport

Meme of The Week

When You’re Ready to Learn More

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2. Tendinopathy 4 phase rehab frame work - My book that walks you through a step by step process of treating tendons

3. Tendininopathy Specific Guides - Learn how to diagnose and manage patellar, achilles, elbow and many more tendinopathies

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