# Novel Use of Generalizability Theory to Optimize Countermovement Jump Data Collection

## TL;DR

This study uses Generalizability Theory to assess the reliability of countermovement jump metrics in college athletes across different sports.

## Contribution

The novel application of Generalizability Theory to optimize CMJ data collection protocols in sports performance assessment.

## Key findings

- Eccentric phase metrics showed lower reliability and often required more than three jumps.
- Phase 1 Concentric Impulse and Scaled Power were reliably measured with three or fewer trials.
- CMJ reliability varies by sport and specific metric, suggesting sport-specific protocol adjustments.

## Abstract

This study aimed to evaluate the reliability of countermovement jump (CMJ) performance metrics across five NCAA Division I varsity sports using Generalizability Theory (G-Theory). Three hundred male athletes from football, hockey, baseball, soccer, and lacrosse performed three or more CMJs on dual-force platforms. G-Theory was applied to identify variance components and determine reliability coefficients (Φ) for 14 key metrics. Metrics requiring more than three jumps to achieve Φ 0.80 were deemed unreliable. Metric reliability varied by sport and phase of movement. Metrics associated with the eccentric phase (e.g., Eccentric Duration, Deceleration Rate of Force Development Asymmetry) demonstrated lower reliability, often requiring >3 jumps. Reliable metrics across sports included Phase 1 Concentric Impulse and Scaled Power, requiring three trials or fewer. CMJ reliability is sport- and metric-specific. Practitioners should prioritize reliable metrics and adjust protocols to balance data quality and practicality, particularly when monitoring eccentric characteristics.