The weekly recap of what is going on in the world of biomechanics.
Special Issue of the Journal of Biomechanics
This week, the Journal of Biomechanics published a special issue, discussing and presenting studies presented at the 3rd International Workshop on Spine Loading and Deformation. Here, we will have a look at two of the canvassed studies.
Selecting the appropriate input variables in a regression approach to estimate actively generated muscle moments around L5/L1 for exoskeleton control:
Researchers from the University of Amsterdam tried to define suitable input parameters that can be used in actuated back support exoskeletons. Those are exoskeletons that use for example motors to support the motion of the wearing person. In this case, they were used to prevent work-related low-back pain. However, these motors (or actuators) need an input variable, so they can apply the right moments at the right point in time. In a way, the actuators “need to know” the generated muscle moment around L5/S1 (the lower back) in order to support properly. For this purpose, the researchers compared datasets consisting of parameters such as spinal load, body kinematics and trunk muscle activation in different loading situations with and without wearing an exoskeleton. According to their findings, the most accurate estimation of the muscle moment around the lower back was possible when the EMG signal of one to two bilateral back muscles (to be precise, they used a third-order polynomial regression of that signal) was combined with the trunk and hip angle. With these input parameters, the control system of the exoskeleton was able to support the worker in the most efficient way.
Tabasi, A., Kingma, I., de Looze, M. P., van Dijk, W., Koopman, A. S., & van Dieën, J. H. (2020). Selecting the appropriate input variables in a regression approach to estimate actively generated muscle moments around L5/S1 for exoskeleton control. Journal of Biomechanics, 109650.
https://doi.org/10.1016/j.jbiomech.2020.109650 
Validation of a wearable system for 3D ambulatory L5/S1 moment assessment during manual lifting using instrumented shoes and an inertial sensor suit:
This paper also discusses moments around L5/S1, but from a different point of view. Researchers from Amsterdam, Boston and Taiwan teamed up with the aim to evaluate the accuracy of a wearable inertial motion capture system (IMC). The system was combined with instrumented shows, to be thought of “wearable force plates” (the Ambulatory-Model). A common inverse dynamic bottom-up model based on data from an optical motion capture system and force plates that was recorded in a laboratory (the Lab-Model) was used as the gold standard to be compared against. The Ambulatory-Model was used once in a bottom-up model using the lower-body IMC kinematics, and once in a top-down model using upper-body kinematics and hand forces. The subjects lifted a 10kg-box from different positions at different velocities in different styles, for example in an asymetric lifting style. The results showed that the root-mean-square errors between the Lab-Model and the top-down Ambulatory-Model was two times smaller than the bottom-up Ambulatory-Model. The averaged error of the top-down Ambulatory model was less than 20Nm (or 10% of the peak extension moment) when copmared to the Lab-Model. This means an top-down model appears to be in favor over bottom-up models when conducting inverse dynamic modelling.
Faber, G. S., Kingma, I., Chang, C. C., Dennerlein, J. T., & van Dieën, J. H. (2020). Validation of a wearable system for 3D ambulatory L5/S1 moment assessment during manual lifting using instrumented shoes and an inertial sensor suit. Journal of Biomechanics, 109671.
https://doi.org/10.1016/j.jbiomech.2020.109671
First Sports Biomechanics Online Lecture
As announced in #CW12, the Sports Biomechanics Online Lecture Series, organized by the ISBS, began last Friday. It was kicked off by Dr. Alasdair Dempsey with his lecture on “Biomechanics and Sports Injury Prevention”. Due to some interruptions by unwanted participants in the virtual conference room, the live broadcast had to be cancelled and the lecture was recorded without an audience. This denied the audience the opportunity to ask direct questions to Dr. Dempsey, but did not reduce the quality of his content.
In any case it is worth to check it out!
Spoiler alert: We can’t stop all sports injuries 😉
