> ## 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 (Normalized)

> Speed of the dominant-side wrist at apex (ball contact), reported alongside the height-normalized dataset.

## Technical Details

* **Variable Type:** Discrete Metric
* **Data Type:** Float
* **Units:** unconfirmed
* **Column Name:** `contact_phase_wrist_velocity_per_ht`
* **Measurement:** Velocity of the dominant-side wrist joint center at [Apex](/biomechanics/activities/tennis/events/apex)

## Description

Contact phase wrist velocity (normalized) is a proxy for racket-head speed at the moment of impact. Despite the `_per_ht` naming, observed values (roughly 700–900 in the Broad Sample at the median) are far too large to be a simple ratio to athlete height, and are more consistent with an angular velocity in degrees/second — this page flags the unit as unconfirmed rather than asserting one until it can be verified against the processing code. This is distinct from [Contact Phase Wrist Velocity](/biomechanics/activities/tennis/metrics/contact-phase-wrist-velocity), which reports a linear speed in meters/second.

## Use Cases

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