> ## 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 Trunk Rotation

> Trunk rotation angle relative to its starting orientation at apex (ball contact).

## Technical Details

* **Variable Type:** Discrete Metric
* **Data Type:** Float
* **Units:** degrees (°)
* **Column Name:** `contact_phase_trunk_rotation`
* **Measurement:** Transverse-plane trunk rotation at [Apex](/biomechanics/activities/tennis/events/apex) (ball contact)

## Description

Contact phase trunk rotation measures how far the trunk has rotated (twisted) by the moment of ball contact, relative to its starting orientation. It reflects how much of the trunk's rotational range has been used by contact, which relates to the [Contact Phase Open Trunk Rotation](/biomechanics/activities/tennis/flags/contact-phase-open-trunk-rotation) movement flag.

## Use Cases

* Trunk rotation timing
* Kinetic chain sequencing
* Related to Contact Phase Open Trunk Rotation flag