> ## 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 Height (Normalized)

> Height of the dominant-side wrist at apex (ball contact), expressed as a multiple of athlete height.

## Technical Details

* **Variable Type:** Discrete Metric
* **Data Type:** Float
* **Units:** × height (ratio to athlete height)
* **Column Name:** `contact_phase_wrist_height_per_ht`
* **Measurement:** Vertical height of the dominant-side wrist joint center above the ground at [Apex](/biomechanics/activities/tennis/events/apex), divided by athlete height

## Description

Contact phase wrist height (normalized) expresses the wrist height at ball contact as a multiple of the athlete's own height, rather than an absolute distance. Normalizing by height makes the metric comparable across athletes of different sizes. Values above 1.0 indicate contact is made above the athlete's own standing height, typical of an overhand serve reaching upward. This is distinct from [Contact Phase Wrist Height](/biomechanics/activities/tennis/metrics/contact-phase-wrist-height), which reports the same measurement as an absolute distance in meters.

## Use Cases

* Contact point consistency across athlete sizes
* Toss and strike height
* Comparison across players or trials