iiinova — where your digital self keeps evolving

Pasha van Bijlert @pashavanb.bsky.social · 08/07/2026

Had a great time presenting my final PhD chapter yesterday at SEB 2026 in Florence @sebiology.bsky.social Did you miss it, or just want to discuss dinosaur or emu locomotion? Come find me at the conference!

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Pasha van Bijlert @pashavanb.bsky.social · 01/07/2026

And if you use direct collocation, you also *must* scale SmoothSphereHalfSpaceForce (Appendix C). Else, small models can literally float above the ground. Default smoothing can cause too much force-build up before actual intersections (demo in @adamkewley.bsky.social's @opensim.bsky.social creator)

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Pasha van Bijlert @pashavanb.bsky.social · 01/07/2026

I took a deep dive into the model and derived equations that make both the static and dynamic behaviour of these contacts completely scale invariant. I then tested the approach on animal models spanning a wide size range.

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Pasha van Bijlert @pashavanb.bsky.social · 01/07/2026

Spheres with Hertz-style deformation and Hunt–Crossley dissipation are a popular way to model contact in musculoskeletal simulations. But - they can be unintuitive, which is a problem because inappropriate contact parameters can over/underestimate energy costs and also cause numerical issues

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Pasha van Bijlert @pashavanb.bsky.social · 01/07/2026

Do you use (musculoskeletal) physics simulations with contact spheres? Then my new paper in @jbiomech.bsky.social is for you! This is my first single-author paper, and the third published chapter from my PhD at @uugeo.bsky.social 🥳 Paper (open access): www.sciencedirect.com/science/arti...

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Pasha van Bijlert @pashavanb.bsky.social · 24/06/2026

Thanks @cjclemente.bsky.social, for the mentorship! Also thank you @taylorjmdick.bsky.social for all of the support and the many inspiring discussions on biomechanics! Not pictured: Chris and Taylor

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Pasha van Bijlert @pashavanb.bsky.social · 24/06/2026

Chris and PhD student Jasmin Annett took us (Finn Roggendorf and me) out to collect biomechanical data from wild emus and kangaroos using drones. Working on two new pipelines for this (using drone photogrammetry - stay tuned, I've paused working on those papers until I submit my thesis...😅)

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Pasha van Bijlert @pashavanb.bsky.social · 24/06/2026

Since I got back from 🇦🇺 I've been so focused on finishing my PhD, I nearly forgot to do a follow-up! Spending ~4 months in @cjclemente.bsky.social's lab was an amazing experience, filled with animal biomechanics and of course - fieldwork! Here's one of our drone shots from the Strzelecki Desert

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Pasha van Bijlert @pashavanb.bsky.social · 19/04/2026

For those who want ellipsoid wrapping in their musculoskeletal models, I've worked out a simple implementation in @blender.org that will soon be added to MuSkeMo (github.com/PashavanBijl...).

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Pasha van Bijlert @pashavanb.bsky.social · 18/09/2025

Made it to the Sunshine Coast to visit @cjclemente.bsky.social and (soon) @taylorjmdick.bsky.social for the next three months! We'll full be doing physics simulations and robot experiments in Chris's lab, and even some fieldwork studying the locomotor biomechanics of wild emus and kangaroos

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Pasha van Bijlert @pashavanb.bsky.social · 21/08/2025

We were recording an outreach video at @naturalis.bsky.social, when I realised we accidentally recreated the T rex chicken meme (with an emu of course ❤️ 🐦❤️)

T skeleton facing an emu skeleton with the text "Remember who you are"

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Pasha van Bijlert @pashavanb.bsky.social · 28/07/2025

For everyone at #ISB2025 interested in musculoskeletal modeling, I'm giving a talk about MuSkeMo, my model construction and visualization tool, Tuesday 11:30 in Room A1 (Session 6A - Musculoskeletal Model Personalization). MuSkeMo is my tool for musculoskeletal model construction in Blender.

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Pasha van Bijlert @pashavanb.bsky.social · 27/06/2025

Here's the segment (in Dutch), at approx. 8:20 - www.rtl.nl/nieuws/uitze... And as a bonus, the most Dutch picture I've ever taken of Ash

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Pasha van Bijlert @pashavanb.bsky.social · 27/06/2025

Enigmacursor, the new neornithischian dinosaur described by @tweetisaurus.bsky.social & @profpaulbarrett.bsky.social, made the Dutch news today! Here's me miming approximately how much bigger Enigmacursor would be than my dog Ash (in his TV debut!) @naturalis.bsky.social

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Pasha van Bijlert @pashavanb.bsky.social · 05/06/2025

Here's me at the Netherlands Society for Evolutionary Biology meeting 2025 (with excellent alignment with a seagull, by Barbara Gravendeel), and the award ceremony at Fysica 2025 (📷 =Nederlandse Natuurkundige Vereniging)

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Pasha van Bijlert @pashavanb.bsky.social · 05/06/2025

Recently, the NL Society for Evolutionary Biology awarded me the "Best Paper Award", and Dutch Physics Magazine gave me the "Picture your research" award, both for our grounded running paper. I often worry that evo biomechanics is too niche for both fields, so this was very encouraging!

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Pasha van Bijlert @pashavanb.bsky.social · 07/01/2025

New paper in @cellpress.bsky.social Current Biology by Karl Bates ea. Karl's physics simulations (validated in a human model) suggest that although Lucy could run - top speed was limited, not leaving much headroom for endurance running. www.cell.com/current-biol...

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Pasha van Bijlert @pashavanb.bsky.social · 30/12/2024

If you've made it this far, allow me to show you the progression my ratite models have made. Thanks for reading! 18/18

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Pasha van Bijlert @pashavanb.bsky.social · 30/12/2024

I'll be cross-posting my other twitter threads here on Bluesky soon as well, so stay tuned if you're interested in animal and dinosaur biomechanics! 16/18

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Pasha van Bijlert @pashavanb.bsky.social · 30/12/2024

Many thanks to the people listed here! 15/18

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Pasha van Bijlert @pashavanb.bsky.social · 30/12/2024

I assembled and visualized the model in @blender3d.bsky.social, using my plugin MuSkeMo: github.com/PashavanBijlert/MuSkeMo/ Compatible (so far) with OpenSim and Gaitsym. Preprint here: doi.org/10.1101/2024... (Yes the model has joints for each neck vertebrae, use it for reaching sims 😅) 13/18

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Pasha van Bijlert @pashavanb.bsky.social · 30/12/2024

Optimizations were done in @opensim.bsky.social Moco. These are all direct collocation simulations. All models, simulator outputs, and several code examples are available on our project page: simtk.org/projects/emi... (Emily stands for Emu Model for Investigating Locomotor dYnamics) 12/18

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Pasha van Bijlert @pashavanb.bsky.social · 30/12/2024

We didn't prescribe postures: the optimizer was free to select any, but selected these postures in response to anatomical changes. By sequentially increasing the target speed, we simulated a full walk-to-run transition, and a run-to-walk transition (from top speed down). 6/18

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Pasha van Bijlert @pashavanb.bsky.social · 30/12/2024

So we did an experiment that's impossible outside the computer: we built a bird, and systematically changed its muscle and tendon anatomy. The muscles were tuned to generate peak forces at columnar, intermediate, and crouched postures, with both rigid and elastic tendons. 5/18

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Pasha van Bijlert @pashavanb.bsky.social · 30/12/2024

Birds have two related features: long tendons (that store energy like springs), and crouched leg postures (so foot-to-hip distance can change, which can "look" like a spring). In a real bird, you can't isolate these two features, making it hard to explain their running style 4/18

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Pasha van Bijlert @pashavanb.bsky.social · 30/12/2024

What is running, actually? In humans, running has an aerial phase, a moment without ground contact. But that's neither true for birds, nor many quadrupedal animals - they sometimes run without an aerial phase, maintaining ground contact with at least 1 foot. 2/18

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Pasha van Bijlert @pashavanb.bsky.social · 30/12/2024

Most birds use a funny running style: grounded running. It's a paradox: GR costs more energy than normal running, but animals usually minimize costs. Do birds waste energy? We resolve this with a model of the emu (the best bird). Published in @science.org Advances last Sept (reposting my x 🧵s) 1/18

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Pasha van Bijlert @pashavanb.bsky.social · 08/12/2024

Haven't logged on here in a while, but for some reason my follows jumped up. Thanks a lot! I'm going to be more active here - expect 3D physics simulations of how modern animals and fossils move, and other sciencey things! For now - here's my emu blooper reel from our recent bird running study

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Pasha van Bijlert @pashavanb.bsky.social · 06/11/2023

The figures from Allen et al 2015 were a fantastic resource! @johnrhutchinson.bsky.social

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Pasha van Bijlert @pashavanb.bsky.social · 06/11/2023

There was also a thresher shark stinking up the lab ( @markscherz.bsky.social for scale)

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Pasha van Bijlert @pashavanb.bsky.social · 06/11/2023

Spent last week doing a muscle dissection of a crocodile at NHM Denmark - thanks a lot @markscherz.bsky.social for enabling this! This big boy had a Caudofemoralis of over 300g! Thanks also to @lauraminifera.bsky.social for letting me take over your couch 😅🐕

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Pasha van Bijlert @pashavanb.bsky.social · 20/10/2023

Trix the T. rex vs the JP jeep - who would win? Come to my talk at #SVP2023 to find out what my newest musculoskeletal (physics) simulations suggest. I'm on Saturday at 9:15 (Fair warning: I'm not actually going to animate the jeep in front of T. rex. Probably) #FossilFriday @naturalis.bsky.social

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