> ## Documentation Index
> Fetch the complete documentation index at: https://docs.uplift.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Contact Phase Open Trunk Rotation

> If trunk rotation at ball contact is above the acceptable threshold.

## Technical Details

* **Variable Type:** Movement Flag
* **Data Type:** Integer
* **Units:** N/A
* **Column Name:** `contact_phase_open_trunk_rotation`
* **Optimal Direction:** Lower is better
* **Unknown Value:** -1
* **Measurement:** Trunk rotation (transverse plane) relative to the serve direction at [Apex](/biomechanics/activities/tennis/events/apex)
* **Threshold:** Trunk rotation greater than -20°

## Description

Contact phase open trunk rotation is a binary indicator that flags when the trunk has rotated too far in the serve direction (past -20°) at the time of ball contact.
This indicates the torso is "opening up" too early relative to the arm and ball.

## Use Cases

* Rotational sequencing assessment
* Mechanics evaluation