The weekly recap of what is going on in the world of biomechanics.
After presenting interesting ways to investigate biomechanical parameters in outdoor sports in the past weeks (have a look here and here), this week we continue with snowboarding. A group of researchers had a look at the snowboard undergoing a carved turn. Enjoy the read!
- Static model of a snowboard undergoing a carved turn: validation by full-scale test
- A public data set of running biomechanics and the effects of running speed on lower extremity kinematics and kinetics
- Bump’em: an open-source perturbation system for studying human balance and gait
- Make sure to never quit learning
Static model of a snowboard undergoing a carved turn: validation by full-scale test
When it comes to situations that are hard to recreate in the lab, there is one method we did not look at recently: It´s modeling. When you want to investigate the behavior of a snowboard but don´t want to take your MoCap-System to the mountains, but you measure as much as possible in your lab, calculate a model (like a digital twin) based on that, apply “real world” conditions and try to validate the outcome.
That is basically what the group around Benoit Caillaud did in this remarkable study, but as you will see it was not as simple as we just outlined. So the group built a static load bench to simulate the loading conditions during a carved turn and used a twin-tip board according to industry standards (this one had a 5.55mm thickness, a wooden core made of ash and two composite skins out of epoxy reinforced fiberglass).
As you can see in the CAD-Image of the setup below, the load bench allowed the team to tilt the board between 40° and 60°, and weight rings were used to simulate the rider´s weight acting on the bindings. Check out this schematic representation of the acting forces and moments from the original paper.
https://link.springer.com/article/10.1007/s12283-019-0307-4/figures/2
After setting up the load bench, the group used a Vicon MoCap system to capture the deformation of the board. A total of 12 measurement sets were defined, differing in total load (20, 40, and 60 kg) and tilt angles (from 39° to 59°). A rather rare method to measure contact pressure between board and surface was used, as the group used a prescale pressure measurement film. That is basically a tape that changes its color depending on the amount of pressure applied. The error for these tapes is reported to be around 10-15% for low-pressure gradients. After scanning the colored film, color densities were converted into MPa.
Now the group had all the necessary data to start building a finite element model, which is something we will not go into detail here. If you are interested in the exact procedure, we´d suggest you read this. After doing simulations with the model, the group was able to compare the experimental results from the load bench with the predictions from the model. They figured out, that the largest discrepancies between model and experiment were in the areas around the bindings, where local deflections could not be captured in the experiment. Along the contact edge the fitting showed a better accuracy, yet on the opposite edge discrepancies grew larger again.
So all in all, the experimental measurements were in good agreement with the numerical predictions. Also the distribution of pressure along the contact edge of the board was in good correlation with the predictions. In the future, a dynamic approach to the modeling process might be insightful, also rethinking the design of snowboards might be influenced by the findings about pressure distribution along the edge.
As always, if this gained your interest we encourage you to read the whole article, which is rich in figures and details, here. Cheers!
Caillaud, B., Winkler, R., Oberguggenberger, M., Luger, M., & Gerstmayr, J. (2019). Static model of a snowboard undergoing a carved turn: validation by full-scale test. Sports Engineering, 22(2), 15.
A public data set of running biomechanics and the effects of running speed on lower extremity kinematics and kinetics
Reginaldo Fukuchi, Claudiane Fukuchi and Marcos Duarte uploaded a data set of running biomechanics and the effects of running speed on lower extremity kinematics and kinetics for open access back in 2017. So if you cannot record your own data due to the current situation, they are available under this link.
The description of the authors’ record is as follows:
“The data set comprises raw and processed lower extremity gait kinematics and kinetics signals of 28 subjects in different file formats (c3d and txt). A file of metadata (in txt and xls formats), including demographics, running characteristics, foot-strike patterns, and muscle strength and flexibility measurements is provided. In addition, a model file (mdh) and a pipeline file (v3s) for the Visual 3D software program are also provided.The data were collected using a three-dimensional (3D) motion-capture system and an instrumented treadmill while the subjects ran at 2.5 m/s, 3.5 m/s, and 4.5 m/s wearing standard neutral shoes.”
Thanks a lot for publishing! It is very rare for scientists to make their entire data sets available to work with.
We like this especially because we at The Biomechanist are planning something similar. In the future, we want to base our entire teaching on this scheme and provide data for practice for everything learned in theory.
Bump’em: an open-source perturbation system for studying human balance and gait
The group around Michael Raitor, Guan Rong Tan, and Steve Collins from Stanford University published all data on their project “Bump’em” this week. This is an open-source, bump-emulation system for studying human balance and gait. The developers promise 200 N perturbations, 45 ms rise time, and material cost lower than $2,500.
Under this link the team has described all necessary information in great detail. You will find component lists, tool lists, 3D models, building instructions for various assembly variations, instructions for software and firmware setup and everything else you might need.
Great work and many thanks for making it Open Access!
Make sure to never quit learning!
In the upcoming week there will be free online webinars again, which you should not miss!
Among others, the Dynamic Walking Conference 2020 will take place on Thursday, May 14th. Everything revolves around the topics of gait, biomechanics, robotics, manipulation and behavior. For this purpose, several parallel chat rooms will be set up, so that not only lectures can be listened to, but also posters with a lot of interaction can be presented and that the social exchange, which is a feature of many conferences, will not be neglected. You can register under this link.
If you missed the webinars of the ISBS Sports Biomechanics Lecture, you should have a look again. In the past weeks there were always new lectures on the biomechanics of diverse sports. Among other tennis, rugby, equestrian riders, soccer, and many more. Have a look at this link to see what you find.
In particular we would like to highlight the lecture on inverse dynamics by Bill Baltzopoulos. In this video he talks about the assessment of loading in the musculoskeletal system, basic steps in modeling, how to approach inverse dynamics, and mechanical misconceptions. At the end of his lecture, he gives a series of guidelines and recommendations that you should definitely follow in this process. Have a look:
