Reliability of the Output Sports Inertial Measurement Unit in Measuring a Reactive Strength Index from the Drop Jump...

Area of Science:

• Sports Science
• Biomechanics
• Human Movement

Background:

• The reactive strength index (RSI) is a crucial metric for assessing athletic performance.
• Accurate measurement tools are essential for monitoring RSI changes and training adaptations.
• Inertial measurement units (IMUs) offer a portable solution for quantifying jump performance.

Purpose of the Study:

• To evaluate the trial-to-trial reliability of the Output Sports IMU for measuring RSI.
• To assess the usefulness of the IMU in detecting meaningful changes in RSI.
• To determine if the IMU can detect the smallest worthwhile change (SWC) in RSI.

Main Methods:

• Twenty-three elite male hurlers performed familiarisation and testing sessions of the Drop Jump (DJ) and 10-5 rebound jump test (10-5 RJT).
• The Output Sports IMU was used to measure RSI during these tests.
• Reliability was assessed using intraclass correlation (ICC) and coefficient of variation (CV).
• Usefulness was determined by comparing typical error (TE) with the smallest worthwhile change (SWC).

Main Results:

• The Output Sports IMU demonstrated high reliability for measuring RSI in both DJ and 10-5 RJT (CV ≤ 10%, ICC ≥ 0.8).
• The typical error (TE) for DJ and 10-5 RJT was 0.09 and 0.08, respectively.
• Both tests, using the IMU, were rated as 'marginal' for detecting the SWC but 'good' for detecting moderate changes in RSI.

Conclusions:

• The Output Sports IMU is a reliable tool for measuring RSI in elite athletes using the DJ and 10-5 RJT.
• The current sensitivity of the IMU is insufficient to detect the smallest worthwhile change in RSI.
• Further research is needed to validate the Output Sports IMU's RSI measurements against criterion methods.