> ## 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              | 1.20 – 1.32               | 0.94 | 1.03 | 1.12 | 1.20 | 1.32 |
| High School        | 1.34 – 1.49               | 0.96 | 1.03 | 1.12 | 1.34 | 1.49 |
| College            | 1.39 – 1.76               | 0.91 | 1.00 | 1.19 | 1.39 | 1.76 |
| Professional       | 1.60 – 1.92               | 1.02 | 1.20 | 1.40 | 1.60 | 1.92 |
| Broad (All Levels) | 1.39 – 1.65               | 0.95 | 1.06 | 1.17 | 1.39 | 1.65 |

## Use Cases

* Power transfer analysis
* Kinetic chain efficiency