It’s World Cup time again, and so far the Anglo-Russian sporting relations seem to be very cordial and without incident. So, we decided to investigate how load cells have been used in football research.
Needless to say we encountered a lot of research into American football players and the impact on their bodies and kit. However we have limited ourselves to research on the original beautiful game, even if it did mean calling it soccer…
Taking it on the shin
FIFA rules require that all players wear shin guards. A study in 2014 used load cells to examine the effectiveness of commercially available polypropylene based shin guards with custom-made carbon fibre guards. Given that lower extremity fractures account for 30-33% of all fractures in football, anything that reduces the number of tibia fractures is important.
However, the BS EN 13061 standard for shin guards is designed to prevent lacerations, contusions and punctures, but not to prevent the more serious tibia fractures.
The 2014 study setup was:
1. A pendulum attached a load cell at the tip and a fixed prosthetic foot equipped with a cleat to simulate an attacker’s foot.
2. An artificial tibia prepared by condensed foam and reinforced by carbon fibers protected with soft clothing.
3. A multifunctional sensor system to record the impact on the tibia…
4. The impact mechanism of the experimental set up was designed to hit the shin guard by the heel of the foot (an area of approximately 20 cm2).
Impressively, the load cell data showed that for the carbon shin guards, less than 11% of the load was transmitted through the guard to the sensors.
Tech for fitness
Load cells can be found all over training gyms and sports research facilities, from the simplest scales to professional force platforms. These systems looks like scales and indeed feature four load cells, but are used to measure forces such as centre of gravity distribution, jump analysis, weight assessment and force production capacity. The measurements can therefore contribute not only to training but the physiotherapy and rehabilitation programmes.
However, commercial force plates can be expensive, and in a country such as Brazil, beyond the means of many institutions. That’s why a team from three Brazilian universities came together to develop a low-cost option that was less than commercial options and more accurate than the cheapest option, the Wii Balance Board! They concluded that:
“The simplicity to fabricate the load cells and for mounting and calibrating the device, indicates the possibility of dissemination of this stabilometric apparatus, serving as a low-cost option for the academic and scientific community.”
On my head, son
Already in this World Cup we have seen teams win through head to ball contact (noticeably Harry Kane’s late header in the England v Tunisia opening match). A team from the Biodynamic Research Corporation investigated accurate ways to measure the impact heading a ball has on neck loading, using a dummy containing load cells.
“The objective of this study was to develop a methodology for accurately calculating the accelerations at the center of gravity of the head and the loads and moments at the occipital condyles. To validate this methodology in a challenging test condition … a Hybrid III dummy were subjected to forehead impacts from a soccer ball traveling horizontally at speeds up to 11.5 m/s. The dummy was also equipped with accelerometers at the center of gravity of the head and load cells in the upper and lower neck.”
The dummy’s load cells neatly validated the measurements taken using the human subjects, providing a testing model that can be replicated with confidence.
“The methods ….for transforming bite block accelerations to the center of gravity of the head and calculating loads at the occipital condyles were validated by their good agreement with direct measurements in Hybrid III dummy tests.”
The RoboCup Humanoid League
Yes, there is a football league for robots!
“In the Humanoid League, autonomous robots with a human-like body plan and human-like senses play soccer against each other. In the KidSize soccer competition teams of four, highly dynamic autonomous robots compete with each other.”.
When preparing for their fifth appearance in the RoboCup Kid-Size Humanoid League, the Rhoban Football Club made some upgrades to their humanoid. Sensing pressures under the feet of these robots is very important, so the team upgraded to:
“A more robust, full Wheatstone bridge, 40kg rated, oﬀ the shelf load cells. These load cells are smaller than the previous ones and are able to handle higher forces because they are made of 3mm thick steel.”
They also changed the design so that the load cells sat on top of the foot plate rather than underneath on the floor surface.
They think it’s all over…
But there’s more! Here are three studies we just didn’t have time to read through during half time oranges:
Load cells for sports research
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