For a summary of this article, see Video 1.

How do Bodies Move and How do They get Injured?

Your muscles and bones work together to help you move. Muscles pull on bones to move your arms and legs around, like a puppet. How hard the muscles pull on the body is called a force. People also feel pushing forces on their bodies every day. For example, when you stand, the ground is pushing on the bottom of your feet. Forces (push or pull) can be good and help people move the way they want to. But too much force can cause the body to break. Forces can act inside the body, like between bones in your knee as you walk. Forces also act outside the body, like the ground pushing on your hand when you fall. When someone gets injured, there is usually a force acting on the outside of the body that causes a chain reaction of forces inside the body. For example, if you lift a very heavy box, your hands and arms might be able to carry the load without getting hurt. But the forces pass all the way through your body and may be too much for your back. Each body part can take a different amount of force before it breaks. These breaking forces are also different for different people.

Why do We Need Computer Models to Study Injury?

If scientists and engineers know how much force causes an injury, they can design safety equipment to make sure that the body does not experience forces close to this point. By making sure the forces that the body experiences are low, we can try to prevent injuries from happening. But injury is a hard thing to study. It is impossible to see or measure the forces inside a living person. People are not usually covered in sensors when they get hurt, and we cannot hurt people on purpose for science.

Computer models can help us calculate the forces that cause an injury by simulating what happened. For example, say a person fell on their elbow and fractured a bone. We might know what this bone looked like before it was injured, and we can use X-rays to see what it looks like after the injury. We might also know what the person was doing when they fell. If we are missing information, like what type of ground the person fell on or how fast they were moving, we guess. The great thing about computer models is that we can try many guesses. We can see how our guesses affect the forces in the elbow. If the elbow fracture was caused by a boy falling at a playground, a safety engineer might use models to decide whether rubber or woodchips are better for a new playground. If the elbow fracture was caused by a teenage girl falling off a skateboard, an equipment company might design new elbow pads and use the models to decide how thick they should be and what material to use for the padding. Computer models can tell us lots of things about an injury that we cannot figure out from images or experiments alone!

How Do Computer Models Work?

Computer models use software to solve math equations, so everything in the model must be turned into math first. Scientists collect information like the shape of the body, outside forces, how muscles and bones move, and properties like how different body parts stretch or break. These are converted into numbers and equations the computer can understand and use as inputs. How the model runs depends on what we want to know. It can be as simple as using a smartphone app that records how the body moves and automatically turns it into a computer model, or it can be very complex and require supercomputers with software that can take days or even weeks to finish one model.

What are the Types of Computer Models Used to Study the Human Body?

There are different types of computer models that help us understand the forces and movements of the human body. Each one is designed to answer specific questions (Figure 1).

Rigid Body Models

Rigid body models take a “big picture” approach to see how the whole body moves together. We imagine the human body as a series of parts, like Lego blocks, connected by joints. These models calculate how outside forces acting on the body (like in a car crash or fall) create forces inside the body, in bones, joints, or tissues. For example, we can use this type of model to estimate the forces at the hip joint during a fall or the forces in the neck during a rear-end collision. We can run lots of simulations quickly by simplifying the body into Lego blocks for each part. This makes it great for testing new safety equipment [1].

Musculoskeletal Models

In some injuries, it is not enough to consider the body as blocks. Sometimes we need to know what these blocks are made of—bones, muscles, tendons, or ligaments. Each of these parts can change the forces inside the body. To understand these parts, scientists use musculoskeletal (MSK) models. MSK models still use rigid bodies to capture the bones of the skeleton but also include individual muscles. These muscles can apply different forces to help us understand how the tissues are affected by impacts or movements, like forces in a slide tackle that cause an ankle sprain. MSK models can also be used to change the properties of muscles, like their shape or stiffness, to model specific muscle conditions. For example, in children with cerebral palsy, scientists can model movement and see how it changes with different treatments [2].

Finite Element Models

Sometimes we need even more detail to understand injuries. For example, what if we want to know where specifically in the bone the injury might happen? Will a force cause a full fracture across the bone or just a small hairline fracture? For shapes and materials as complex as human body parts, there are no math equations to calculate what is happening in each tissue. Instead, we use finite element models that divide the complex body part into very small blocks, called elements. We use computers to calculate what happens in each block in situations where people experience forces. The blocks with the highest forces can tell us which body area is most likely to become damaged [3].

What Are Some Applications of Computer Models?

We have already talked about a few areas where computer models can help us, but there are lots of other areas where they might be useful. For example, if we want to design a new car, we cannot test its safety with real people inside. So, engineers can use rigid body models to figure out what happens to a person during a car crash. In sports, we might use musculoskeletal models to figure out what happens if you twist your ankle while trying to jump rope. We can also figure out the forces on an athlete’s joints when they run. This information can help coaches train athletes to use better techniques or suggest exercises to strengthen specific muscles.

Engineers are always looking for ways to make the environment safer to prevent injuries. So, any time you see safety equipment—seatbelts in cars, helmets in sports, fall protection in a construction zone—these all need to be designed and tested. How do you know if a seatbelt will protect you? Or which car seats keep babies safest? Computer models are a very important part of making sure the safety equipment we make is keeping people safe. By testing different designs in computer models, we can estimate the outside forces experienced by the body. We can keep making design changes to make sure these forces stay below the levels that could cause an injury [4].

Can We Solve Everything Using Computer Models of the Human Body?

While computer models can help us answer key questions about the how the human body works, it is not as easy as it seems to make a model. We cannot use computer models for everything. First, everyone is different. We have different heights and weights, and even on the inside, the shapes of our bones and muscles are unique. This means that computer models need to capture different people [2]. Second, what we get out of these models depends on what we put in. For example, we may not have all the inputs we need to run a model. So, scientists try different guesses until the model’s results match what they expect to see. While models can tell us a lot about safety and the human body, they are not the only way to figure these things out. Sometimes, experimental tests are used, and sometimes experimental tests are combined with models to give us a better picture. It takes years of research to build just one model, and many scientists build on each other’s work to improve models. There is still lots of work left to do before we can completely understand the human body, but each model helps us get a little bit closer.

Glossary

Video 1: ↑ An overview of how scientists use computer models to study our body.

Force: ↑ A push/pull on an object. Forces can come from inside the body (like muscles pulling on bones) or outside the body (like gravity which keeps you on the ground).

Computer Model: ↑ A digital version of a real-life object, built on a computer so scientists can test ideas and situations to see what might happen without using real people.

Software: ↑ A set of computer programs that tells a computer what to do. Special software can run on computers to solve complicated math problems.

Supercomputer: ↑ A very powerful computer that can solve very large problems faster than a regular computer.

Rigid Body Models: ↑ Computer models that simplify the body into connected parts, like Lego blocks, to study how the body moves and how outside forces affect it.

Musculoskeletal Models: ↑ Computer models that include both bones and muscles to study how these tissues work together to create movement or cause injury.

Cerebral Palsy: ↑ A condition that affects movement, balance, and posture in affected people.

Finite Element Models: ↑ Computer models that break a body part into many tiny pieces (elements) so scientists can see exactly how forces are spread within tissues and where damage might occur.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

This work was supported by the Craig H. Neilsen Foundation (997610; NO), Michael Smith Health Research BC (RT-2021-1722; NO), Natural Sciences and Engineering Research Council of Canada Discovery Grant and Discovery Accelerator Supplement (RGPIN06382 and RGPAS-522659; CS), and a Natural Sciences and Engineering Research Council Canada Graduate Scholarship (DZ).

AI Tool Statement

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