> ## 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.

# Sit

> The instant the pelvis returns to the seated position at the end of each sit-to-stand repetition.

## Technical Details

* **Variable Type:** Event
* **Data Type:** Integer
* **Units:** Frame number
* **Column Name:** `sit_frame`
* **Required for QA:** True
* **Recurring:** One frame per repetition
* **Measurement:** First frame after the descent at which the pelvis is within 10% of the repetition's descent amplitude above the low point the descent ends at

## Description

Sit marks the moment the person returns to the chair at the end of a repetition.
For each repetition, Uplift follows the descent down to the low point it ends at and takes the first frame within 10% of the descent amplitude above that low point.
As with [Seat Off](https://docs.uplift.ai/biomechanics/activities/stability/sit_to_stand/events/seat-off), the threshold is referenced to each repetition's own low point so touch-and-go repetitions are detected.

Sit ends the [Descent](https://docs.uplift.ai/biomechanics/activities/stability/sit_to_stand#phases) phase.
If the capture ends before the person sits back down, the final repetition has no Sit and the capture fails QA.

## Use Cases

* End of each repetition and of the [Total Time](https://docs.uplift.ai/biomechanics/activities/stability/sit_to_stand/metrics/total-time)
* [Descent Time](https://docs.uplift.ai/biomechanics/activities/stability/sit_to_stand/metrics/descent-time) and [Repetition Time](https://docs.uplift.ai/biomechanics/activities/stability/sit_to_stand/metrics/repetition-time)


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