Countermovement Jump Force-Time Curve Analyses: Reliability and Comparability Across Force Plate Systems

Area of Science:

• Biomechanics and Human Movement Analysis
• Sports Science and Performance Testing
• Measurement Science and Instrumentation

Background:

• The increasing use of commercial force plates for automated force-time analyses necessitates an understanding of their inter-system agreement.
• Previous research has not comprehensively compared the reliability and comparability of countermovement jump (CMJ) metrics across different force plate systems.
• Variations in metric definitions and units across platforms may impact data interpretation and application in human performance.

Purpose of the Study:

• To compare countermovement jump (CMJ) metrics across three popular force plate systems: Vald ForceDecks (FD), Hawkin Dynamics (HD), and Sparta Science (SS).
• To assess the reliability and comparability of key CMJ performance indicators, including jump height, rate of force development (RFD), and reactive strength index (RSI), across these systems.
• To inform human performance practitioners about potential discrepancies and biases when using different force plate technologies.

Main Methods:

• Twenty-two subjects performed countermovement jumps (CMJs) on FD, HD, and SS force plate systems, with multiple trials and rest periods.
• Baseline testing was conducted three times to evaluate test-retest reliability for modified reactive strength index (mRSI) and RFD.
• Concordance correlation coefficients (CCC) and bias analyses were used to quantify agreement and identify systematic or proportionate differences between systems.

Main Results:

• Poor test-retest reliability was observed for mRSI and RFD across all systems.
• FD and HD showed acceptable agreement for several metrics (e.g., jump height, relative force, impulse), but RFD exhibited systematic and proportionate bias.
• Sparta Science (SS) tended to overestimate jump height and RSI compared to FD and HD, though jump height agreement was acceptable (CCC = 0.92-0.95). SS load (eccentric RFD) showed acceptable agreement with HD braking RFD (CCC = 0.91) and FD deceleration RFD (CCC = 0.81-0.87), but with bias. SS explode (concentric force) had acceptable agreement with FD and HD but systematically lower values.

Conclusions:

• Significant inconsistencies exist in countermovement jump (CMJ) metric calculations and reporting across different force plate systems (FD, HD, SS).
• Practitioners must be aware of systematic biases and differences in metric definitions (e.g., units of measurement) when comparing CMJ data obtained from various platforms.
• Careful consideration of these inter-system variations is crucial for accurate interpretation and application of performance data in training and athlete monitoring.