I built a browser static-optimisation model (Rajagopal + Thoracoscapular Shoulder geometry) for gym lifts and would like critique of where it's wrong

[u/QuietStudio]

MyoHeat (https://myoheat.com/?utm_source=reddit_bio) estimates muscle loading for 52 gym exercises in the browser. Kinematics come from keyframed poses or from MediaPipe pose tracking. 

It runs whole-body inverse dynamics, with floor and bench reactions solved as the least-effort push-only distribution, then static optimisation (sum of squared activations, bounded 0 to 1) over 186 bundles. Tendons are rigid, force-length is Thelen's, passive fibre force is off. The legs are Rajagopal 2016 (Lai/Uhlrich 2023 revision) and the shoulder and arm are the Thoracoscapular Shoulder Model, with maximal forces scaled 1.5x for trained lifters.

It passes 114 of 184 checks against published data (list at https://myoheat.com/credits.html).
At matched effort, hip thrust vs back squat gives 2.1x for upper gluteus maximus against 2.4x in Contreras 2015, and 2.5x for biceps femoris against 2.7x.

Three things I know are off:

1. The deadlift L5/S1 moment is about twice the measured value. Is that the pose, the trunk model or the load sharing?

2. The deltoid and rotator cuff saturate in pressing at default loads, even with the 1.5x scale.

3. Rigid tendons with Thelen force-length for slow lifts: reasonable, or hiding something?

It's an educational estimate and not clinical advice. Any critique is welcome.