> ## 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.

# X Factor Zero Crossing

> When the shoulder-hip separation crosses zero after Max X Factor. This marks the transition from loading to acceleration phase as the shoulders catch up to the hips.

## Technical Details

* **Variable Type:** Event
* **Data Type:** Integer
* **Units:** Frame number
* **Column Name:** `x_factor_zero_crossing_frame`
* **Measurement:** Zero crossing of shoulder-hip separation
* **Timing:** After max X factor event

## Description

The X factor zero crossing event marks the transition from the loading phase to the acceleration phase when the shoulder-hip separation crosses zero, indicating that the torso rotation angle catches up to the pelvis rotation angle.

## Use Cases

* Phase transition analysis
* Acceleration timing assessment
* Swing sequence evaluation
* Power transfer analysis