> ## 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.

# Single Leg Stance

> Biomechanical analysis of single leg stance balance assessment, including sway measurements and trunk lean evaluation.

## Overview

Single leg stance is a fundamental balance exercise and a common component of everyday movement, from walking and running to climbing stairs.

## Instructions

Stand upright on one leg while the other leg is lifted off the ground. For greater challenge, repeat with eyes closed.

## Example Videos

### Eyes Open

### Left

<Frame>
  <video controls src="https://uplift-docs-assets.s3.amazonaws.com/stability/stability-single_leg_stance-eyes_open-left_combined.mp4" />
</Frame>

### Right

<Frame>
  <video controls src="https://uplift-docs-assets.s3.amazonaws.com/stability/stability-single_leg_stance-eyes_open-right_combined.mp4" />
</Frame>

### Eyes Closed

### Left

<Frame>
  <video controls src="https://uplift-docs-assets.s3.amazonaws.com/stability/stability-single_leg_stance-eyes_closed-left_combined.mp4" />
</Frame>

### Right

<Frame>
  <video controls src="https://uplift-docs-assets.s3.amazonaws.com/stability/stability-single_leg_stance-eyes_closed-right_combined.mp4" />
</Frame>

## Dimensions

Required inputs for processing:

* **Footedness:** The foot maintaining balance *\['left', 'right']*

## Generic Outputs

Every capture includes session metadata, standard joint angle/velocity time series, and 3D keypoint positions common to all movements. See [Generic Outputs](/biomechanics/activities/generic_outputs) for the full list.

## Events

| Metric     | Description                        | Column Name |
| ---------- | ---------------------------------- | ----------- |
| Initiation | the start of the single leg stance | \`\`        |
| End        | the end of the single leg stance   | \`\`        |

## Discrete Metrics

| Metric                       | Units   | Description                                                                        | Column Name                                      |
| ---------------------------- | ------- | ---------------------------------------------------------------------------------- | ------------------------------------------------ |
| Stance Time                  | seconds | Duration of the single leg stance                                                  | `single_leg_stance_stance_time`                  |
| Stance Time Clearance        | -       | Whether stance time passed threshold (1) or not (0)                                | `single_leg_stance_time_clearance`               |
| Mean Sway Velocity           | m/s     | Average velocity of body center of mass during stance                              | `single_leg_stance_mean_sway_velocity`           |
| Percentile 75 Sway Velocity  | m/s     | 75th percentile of sway velocity during stance                                     | `single_leg_stance_percentile75_sway_velocity`   |
| Mediolateral Displacement    | meters  | Maximum range of mediolateral (left/right) displacement of center of mass          | `single_leg_stance_mediolateral_displacement`    |
| Anteroposterior Displacement | meters  | Maximum range of anteroposterior (forward/backward) displacement of center of mass | `single_leg_stance_anteroposterior_displacement` |
| Sway Area                    | m²      | Square area of sway calculated from the product of ML and AP displacement          | `single_leg_stance_sway_area`                    |
| Left Trunk Lean              | degrees | Maximum left trunk lean in frontal plane                                           | \`\`                                             |
| Right Trunk Lean             | degrees | Maximum right trunk lean in frontal plane                                          | \`\`                                             |
| Excessive Trunk Lean         | -       | Whether trunk lean exceeds threshold (1) or not (0)                                | `single_leg_stance_excessive_trunk_lean`         |

## Notes

* Kinematic data typically captured at 30-60 Hz for stability activities
* Stance time clearance threshold is set to 10 seconds
* Excessive trunk lean threshold is set to 10 degrees