> ## 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.

# Low Arm

> The low point of the dominant arm just prior to ball contact.

## Technical Details

* **Variable Type:** Event
* **Data Type:** Integer
* **Units:** Frame number
* **Column Name:** \`low\_arm\_event'
* **Required for QA:** False
* **Measurement:** Frame at which the dominant arm reaches its lowest point before the upward swing between [Ball Release](/biomechanics/activities/tennis/events/ball-release) and [Apex](/biomechanics/activities/tennis/events/apex) events

## Description

Low Arm marks the instant when the dominant (serving) arm reaches its lowest point during the preparation phase, after [Ball Release](/biomechanics/activities/tennis/events/ball-release) and before the [Cocking](/biomechanics/activities/tennis/overhand_serve#phases) phase.
It defines the end of the loading phase and the start of the cocking phase.

## Use Cases

* Loading phase duration (ball release to low arm)
* Cocking phase start (low arm to max shoulder ER)
* Serve rhythm and timing