> ## 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.

# Cocking Phase Max Shoulder External Rotation

> Maximum amount of shoulder external rotation during the cocking phase of the serve.

<img src="https://mintcdn.com/upliftlabs/Ku7T6jLWrJyoK7uq/biomechanics/activities/tennis/images/shoulder-external-rotation.png?fit=max&auto=format&n=Ku7T6jLWrJyoK7uq&q=85&s=15d98ed93029b9a4a40201eaad5b1191" alt="Shoulder external rotation during cocking" width="500" height="500" data-path="biomechanics/activities/tennis/images/shoulder-external-rotation.png" />

## Technical Details

* **Variable Type:** Discrete Metric
* **Data Type:** Float
* **Units:** degrees (°)
* **Column Name:** `cocking_phase_max_shoulder_external_rotation`
* **Measurement:** Maximum shoulder external rotation angle marks the end of cocking phase at [Max Shoulder ER](/biomechanics/activities/tennis/events/max-shoulder-er))

## Description

This metric is the maximum external rotation of the dominant shoulder during the cocking phase.
Greater external rotation permits more range of motion to accelerate into the serve.
The instant of maximum is the [Max Shoulder ER](/biomechanics/activities/tennis/events/max-shoulder-er) event.

## Use Cases

* Shoulder loading, range of motion, and injury risk context
* Technique and power potential