> ## 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.

# Apex

> Maximum height of the dominant-side wrist joint center during the serve. A proxy for ball contact.

## Technical Details

* **Variable Type:** Event
* **Data Type:** Integer
* **Units:** Frame number
* **Column Name:** 'apex\_event'
* **Required for QA:** True
* **Measurement:** Frame at which the dominant-side wrist reaches maximum height

## Description

Apex marks the instant when the dominant-side wrist joint center reaches its maximum height during the serve, which typically coincides with ball contact.
Contact-phase metrics (elbow flexion, shoulder abduction, X factor, trunk tilt, wrist velocity, wrist height) are reported at this event.

## Use Cases

* Ball contact timing
* Contact-phase metrics (joint angles, wrist velocity, wrist height)
* Acceleration phase end and follow-through start