> ## 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.

# Trunk to Arm Speed Up

> Ratio (multiplication factor) of speed increase from trunk to arm. This measures the efficiency of power transfer from the core to the upper body.

## Technical Details

* **Variable Type:** Discrete Metric
* **Data Type:** Float
* **Units:** ratio
* **Column Name:** `trunk_to_arm_velocity_speedup`
* **Aggregation:** mean
* **Precision:** 2
* **Calculation:** Peak arm angular velocity / Peak trunk angular velocity
* **Optimal Range:** 1.2-1.8
* **Optimal Direction:** Higher is better

## Description

Trunk to arm speed up measures the multiplication factor of velocity increase from the trunk to the arm, indicating the efficiency of power transfer through the kinetic chain.

## Normative Ranges

Percentile distributions by competition level from the 2026 Q1 dataset; the optimal range spans the 75th–90th percentiles.

| Population         | Optimal Range (75th–90th) | 10th | 25th | 50th | 75th | 90th |
| ------------------ | ------------------------- | :--: | :--: | :--: | :--: | :--: |
| Youth              | 1.31 – 1.51               | 0.89 | 1.03 | 1.14 | 1.31 | 1.51 |
| High School        | 1.31 – 1.51               | 0.89 | 1.03 | 1.14 | 1.31 | 1.51 |
| College            | 1.37 – 1.54               | 0.92 | 1.06 | 1.21 | 1.37 | 1.54 |
| Professional       | 1.37 – 1.54               | 0.92 | 1.06 | 1.21 | 1.37 | 1.54 |
| Broad (All Levels) | 1.36 – 1.55               | 0.90 | 1.04 | 1.19 | 1.36 | 1.55 |

## Use Cases

* Power transfer analysis
* Kinetic chain efficiency