> ## 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.

# Acceleration Phase Max Knee Extension Velocity

> Maximum knee extension velocity of the front and back leg during the acceleration phase.

<img src="https://mintcdn.com/upliftlabs/Ku7T6jLWrJyoK7uq/biomechanics/activities/tennis/images/knee-extension-velocity.png?fit=max&auto=format&n=Ku7T6jLWrJyoK7uq&q=85&s=f00cf9747243ebadb98196e77b8e3122" alt="Knee extension velocity during acceleration" width="500" height="500" data-path="biomechanics/activities/tennis/images/knee-extension-velocity.png" />

## Technical Details

* **Variable Type:** Discrete Metric
* **Data Type:** Float
* **Units:** degrees/second (°/s)
* **Column Name:** `acceleration_phase_max_front_knee_extension_velocity` or `acceleration_phase_max_back_knee_extension_velocity`
* **Measurement:** Maximum knee extension angular velocity during the acceleration phase ([Max Shoulder ER](/biomechanics/activities/tennis/events/max-shoulder-er) to [Apex](/biomechanics/activities/tennis/events/apex))

## Description

This metric describes the maximum knee extension velocity for each leg during the acceleration phase of the serve.
The maximum value should align with the jumping portion of the serve, correlating with jump height.
It reflects lower-body drive and contribution to the kinetic chain as the player extends toward ball contact.

## Use Cases

* Lower-body drive and timing
* Kinetic chain assessment
* Technique comparison