# Stereotypical force patterns of the elephant trunk in planar reaching movements

## TL;DR

Researchers developed a model to understand how elephant trunks move by linking trunk shape to internal forces, enabling insights into their dexterous motion.

## Contribution

The study introduces linear laws that map trunk shape to muscle-analogue forces in a rod-based model, simplifying complex trunk dynamics.

## Key findings

- The model predicts reaching trajectories with tip-position errors below 8%.
- Force-shape mappings reveal consistent internal force patterns for specific trunk postures.
- The framework reduces high-dimensional dynamics to simple linear relationships for muscle-force inference.

## Abstract

The elephant trunk is a highly dexterous muscular hydrostat whose continuous, distributed deformations pose significant challenges for mathematical modeling. We introduce linear “stereotypical” laws that map desired trunk configurations, parameterized by curvature and length, directly to the internal muscle-analogue forces required in our rod-based dynamic model. The trunk is represented as a simplified multi-segment structure of point masses linked through longitudinal and radial muscle analogues and connective tissue, all modeled using rods. Using these laws, the model predicts biological reaching trajectories with tip-position errors below 8% while maintaining hydrostatic volume across trials. The resulting force-shape mappings reveal consistent, repeatable internal force patterns underlying trunk postures, providing a compact representation of actuation strategies that generate specific planar shapes. By reducing high-dimensional continuum dynamics to simple linear relationships, this framework preliminarily enables the inference of muscle-force distributions from shape configurations, laying the groundwork for deeper exploration of the elephant trunk motion strategies and their translation into advanced robotic systems control.

•A rod-based dynamic model is developed to study planar reaching in the elephant trunk•Linear laws map trunk curvature and length to internal muscle-analogue forces•Force correlations reflect muscular principles underlying elongation and bending

A rod-based dynamic model is developed to study planar reaching in the elephant trunk

Linear laws map trunk curvature and length to internal muscle-analogue forces

Force correlations reflect muscular principles underlying elongation and bending

Applied sciences; Engineering; Robotics