Safety equipment for sport

Whether it’s helmets, protective pads or mouthguards, most personal protective equipment (PPE) in sports is designed to protect against impact.

The Research Centres for Musculoskeletal Science and Sports Medicine and Advanced Materials and Surface Engineering bring together an interdisciplinary team of researchers working across biomechanics, sports medicine and engineering.

This work will also be part of the Manchester Metropolitan University Institute of Sport, a new hub for sports performance, teaching and research expertise.

A strand of research focuses on designing, modelling and testing PPE to ensure that equipment worn by sports participants provides evidence-based protection from injury.

Dr Tom Allen leads on PPE engineering, using computerised methods to study how sports equipment behaves during impact.

Tom’s background in sports engineering led to a spell in the innovation team at Adidas and working on tennis rackets with Prince in Italy.

Tom explains: “When I finished university, I worked in Germany for Adidas designing shoes. I was in the engineering team providing engineering expertise on projects. Then I did a PhD at Sheffield Hallam University modelling tennis rackets with Prince, going to Italy and working with them. Since then, I’ve focused more on injury prevention.”

Safety on the slopes

Working in collaboration with Sheffield Hallam University, Tom and Dr Caroline Adams have looked in-depth at wrist protection in snowboarding.

“When I was the Associate Editor at the Sports Engineering journal, we ran a special issue on Winter Sports. The issue included a white paper from the International Society of Snowsport Safety, which outlined the issue of wrist injuries among snowboarders. About a third of snowboarding injuries are to wrists - mainly among beginners and children who are more likely to put their hands out when they fall over.

“They outlined the problem in the paper, said what the issues were and what needed to be done. I thought it was interesting and began working in that area to develop an International Standard for snowboarding wrist protectors.”

Tom and his collaborators developed and validated a set of stiffness tests for snowboarder wrist protectors, with a view to determining which design features are effective at preventing wrist hyperextension during falls.

But how do you test a piece of equipment designed to protect someone from injury?

“Much of the work we do is in a lab mimicking injurious scenarios in experiments without people, we tend to use surrogates instead. With the wrist protector work, we developed a surrogate arm that we use for testing. The surrogate is essentially a hand and forearm connected by a simple joint. Much of the work we’re doing is developing that surrogate and associated computer models for use as wrist protector design tools. A recent PhD graduate from our team, Dr Chloe Newton-Mann, developed the computer models during her PhD.

“We have two main tests. One involves a surrogate 3D printed in plastic - we pull the hand backwards slowly to measure the protector stiffness. A second test involves an impact onto the surrogate – we drop a mass onto the palm region of the protector to force the hand backwards, mimicking hyperextension during a fall. The surrogate in the impact test is similar, but it has both metal and plastic components, and an embedded sensor to measure the angle of the hand. The rig for this impact test is located at Sheffield Hallam University where Caroline did her PhD.  

“One of our PhD students, Gemma Leslie, is developing the surrogate, adding a layer of silicone to mimic skin and soft tissue, and we’re looking at embedding pressure sensors as well. As we’re pulling the hand backwards to mimic hyperextension, we can measure where the highest pressure is under the splints of the protector. For instance, if you have a long splint stretching down the forearm and your wrist hyperextends during a fall, the long splint might increase the likelihood of a fracture at the end of the splint. We’re investigating forces at the end of splints.

“During impact tests, we measure the angle of the striker, and the direction and size of the forces the striker causes while filming the surrogate with high-speed cameras. The cameras allow us to see what’s happening and interpret the results from sensors more easily.”

The creation of a forearm and wrist surrogate to simulate and measure forces during a fall means we can make recommendations on specifications for snowboarder wrist protectors.

The work informed the new International Standard ISO 20320 “Protective clothing for use in snowboarding - Wrist protectors - Requirements and test methods”.

All wrist protectors sold in the EU will comply with this standard, which should reduce the risk of serious wrist injuries for wearers.

PLAYER WELFARE IN RUGBY

Unlike snowboarding, where harmful impacts happen accidentally, rugby is a game built on tackling – meaning collisions can be unavoidable.

Tackling can take place anywhere on the field of play, and although strict rules help to ensure a fair contest and safe technique, the game still involves the force of two or more players colliding together.

Tom is working on a project with PhD student Adil Imam on padded clothing to benefit player welfare with World Rugby, the world governing body for rugby union.

“Rugby padding is for preventing skin and soft tissue injuries like cuts and lacerations, not severe injuries from impact like fractures and dislocations,” says Tom.

“For the current testing, there is a steel cylinder that serves as a basic representation of a shoulder. We put the padding on top of the cylinder and impact test it by dropping a mass onto it while measuring the force.

“What our collaborators at the University of Sheffield have done is taken that steel cylinder and reduced the size of it to accommodate a layer of silicone to represent soft tissue, much like with the wrist surrogate. On top of the silicone, we have a skin simulant to make it more like someone’s shoulder.

“It’s really about getting the stiffness of the shoulder surrogate correct. Angus Hughes, a PhD student at the University of Sheffield, is working on the project incorporating bones into the surrogate.”

How footballs deform

In football, one of the most frequent forms of impact for players is with the football itself.

There is growing concern among ex-footballers, politicians, medical professionals and the research community about the links between heading a football and long-term brain injuries caused by repeated head trauma.

In the UK, a joint committee of national governing bodies is working towards protocols that could make England the first country to limit heading in football training – from youth level all the way up to full-time professionals.

It’s clear that heading is on the mind of the beautiful game.

Tom and his team are working with FIFA, the international governing body of football, after winning funding from the FIFA Football Technology and Innovation Research Scheme.

“Most of our work focuses on dynamics in sport; how things collide with potential to cause injury. We submitted a project proposal to develop an open-source software tool that uses camera footage to measure how footballs deform on impact, with implications for head injuries and ball regulation.”

MOUTHGUARD FABRICATION

In high impact and combat sports, mouthguards can protect from injury by offering vital protection to teeth and gums - whether it’s from a jab in boxing, a high tackle in rugby, or a stray puck in hockey.

There are three types of mouthguards. The stock mouthguard is a horseshoe-shaped product available from many sports outlets. Then there is boil and bite - you buy the product, take it home and place it in warm water. It softens, allowing you to bite it and mould it to the shape of your mouth. The other type is a bespoke option made by a dentist, customised to your dentition.

Dr Keith Winwood’s work focuses on personal protective equipment to reduce maxillofacial and dental injury, alongside research within musculoskeletal science. His team attempts to underpin new techniques to enhance mouthguard fabrication, as well as promoting their usage.

Keith explains: “The main challenge is that there are differences between individual’s dentition and jaw profiles. Mouthguards are thin devices, and you’re trying to limit the force of an impact from a ball or a solid object striking the mouth. The most important factors are protection and making sure that the individual wears it.”

Keith’s team, including former PhD student Dr Tim Farrington, developed a novel adaptation in the fabrication process via a model angulation technique. The adaptation helped to reduce variability in thickness during the production process of custom-made mouthguards, which could also reduce cost and manufacturing time.  

The team has also explored areas of comfort, retention and physiological parameters in relation to mouthguard design working with rugby and boxing participants.

“We did a survey that showed the main reasons people avoided the use of mouthguards actually related to discomfort, difficulties in breathing and communication. This is really important, particularly in team sports like rugby,” says Dr Raya Karaganeva.

They found that the design of a mouthguard could potentially influence comfort and that there was no negative effect of mouthguard design or usage on respiratory function. Comfort can be key to whether a participant wears the equipment or not.

The team shared their research findings through workshops and publications with dental professionals and industrial partners. As well as collaborating with the Dental Technologists Association and the injury prevention charity Dental Trauma UK to highlight the importance of mouthguard usage to trainee physical education teachers.

Auxetic materials

Another strand of Tom’s research is working with auxetic materials alongside Dr Olly Duncan, in collaboration with Sheffield Hallam University.

Auxetics expand or fatten when you pull them. Whereas most materials will get thinner as you pull them - you can try this yourself with an elastic band - auxetic materials do the opposite and expand.

“That’s what we call a negative Poisson’s ratio,” says Tom. “Poisson’s ratio is a measure of how much something expands or contracts laterally, relative to how much you’re stretching or compressing it. If Poisson’s ratio is negative, it means the material expands laterally, or fattens, when stretched. The other way to think of it is that compression will make an auxetic material contract laterally, or get thinner.

“A key property of auxetic sheets is that they form a dome shape when you bend them, because of the way they expand on the outside during bending – helping them to fit rounded body parts like a head, knee or elbow. One reason auxetic materials should be good for protective equipment is that when they are impacted with a concentrated load – such as a rock, stud or sports ball - they contract inwards, so material ‘flows’ to defend the impacted area.”

Tom and his collaborator’s research has shown that a helmet fitted with auxetic foam could reduce the severity of an impact more effectively than a helmet fitted with conventional foam.

“One of the simplest ways to get a negative Poisson’s ratio material is to take a sheet of conventional foam and then cut an auxetic pattern into it with a laser cutter. This is the approach Charlotte Moroney took, a PhD student from the Manchester Fashion Institute supervised by Dr Tasneem Sabir. The foam has normal properties, but the pattern allows it to expand when you pull it – that’s what we’re exploring with rugby padding.

“You can’t just take a big sheet of foam and stick it on your shoulder. It just wouldn’t fit. We have to cut them, segment them or mould them in a certain way to fit around the shoulder.

“The simplest way to think of auxetics is that the unique properties are due to patterns or shapes within the structural architecture. It’s often not the material itself; it’s more the way the internal structure of the material is shaped to move in a certain way. For example, PhD student Todd Shepherd is using a combination of computer modelling and additive manufacturing to design auxetic materials with different structural architectures.”

Tom is also applying these materials to help children engage in sport, exercise and play.

“In collaboration with Loughborough University and the University of Leeds, we’re looking at applying auxetics to prosthesis socket liners for children. The idea is that such an auxetic liner should be able to move, conform and fit to the residual limb.

“The liner should be able to adjust in shape during the day – the limb size changes during the day with temperature and other factors – but also over extended periods of time with growth, and the liner should be more breathable.”

Sensing change

Aside from auxetics, Tom looks towards the use of sensors as an upcoming trend in both injury prevention and amateur sporting use.

Sensors are already widely used in commercial products like smartphones - in global positioning systems and pedometers to track runs and daily steps, or sleep trackers to analyse body movement to check if you are asleep.

For use in injury prevention, it’s less simple.

“There’s been issues with people putting sensors on helmets, collecting data and then suggesting sporting impacts are more severe than expected. Recent work suggests it’s the helmet that is moving very quickly, and the head is moving much slower underneath. Using sensors to study injury risk is challenging.

“There will be further uptake in sensors which, from a research perspective, should be interesting and insightful. We can use them to measure forces and acceleration to inform equipment design. The average person who goes and buys their new shoes, tennis racket or bike isn’t looking for a lab tool, they just want to know it’s going to work properly, but incorporating sensors may help them to improve their technique or performance.”