> ## 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.

# Trunk Coil

> Maximum amount of trunk twist rotation away from the serve direction (preloading the twist before the serve).

## Technical Details

* **Variable Type:** Discrete Metric
* **Data Type:** Float
* **Units:** degrees (°)
* **Column Name:** `trunk_coil`
* **Measurement:** Maximum trunk twist rotation away from the serve direction during the preparation/loading phase
  * how much the trunk is "coiled up" before uncoiling toward contact

## Description

Trunk coil is the maximum twist rotation of the trunk away from the serve direction during the early phases of the serve.
It reflects preloading of the trunk before the acceleration phase and contributes to [Trunk Stretch](/biomechanics/activities/tennis/metrics/trunk-stretch) (twist range of motion).

## Use Cases

* Coiling and loading assessment
* Trunk contribution to kinetic chain
* Comparison with pelvis coil and stretch metrics