> ## 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 Wrist Velocity

> Linear speed of the wrist joint center at apex (ball contact).

## Technical Details

* **Variable Type:** Discrete Metric
* **Data Type:** Float
* **Units:** meters/second (m/s)
* **Column Name:** (implementation-specific)
* **Measurement:** Linear velocity magnitude (or component) of the dominant-side wrist joint center at [Apex](/biomechanics/activities/tennis/events/apex) (ball contact)

## Description

Contact phase wrist velocity is the linear speed of the wrist at ball contact. It is a proxy for racket-head speed and reflects the outcome of the kinematic chain at the moment of impact.

## Use Cases

* Racket speed proxy and serve power
* Technique and consistency
* Comparison across players or trials