Reliability of the Output Sports Inertial Measurement Unit in Measuring a Reactive Strength Index from the Drop Jump and 10-5 Rebound Jump Test

This study examined the trial-to-trial reliability and usefulness of the Output Sports inertial measurement unit (IMU) in measuring reactive strength index (RSI) derived from the Drop Jump (DJ) and 10-5 rebound jump test (10-5 RJT). Twenty-three male elite intercounty hurlers (mean ± SD; age: 24.3 ± 3.7 years, mass: 88.0 ± 6.3 kg, height: 183.8 ± 5.8 cm, experience at elite level: 5.8 ± 3.8 years) performed three trials each of the DJ and 10-5 RJT, on familiarisation and testing days. There was one week between familiarisation and testing. Reliability was determined by intraclass correlation (ICC) and coefficient of variation (CV) analyses. Usefulness was assessed by comparing typical error (TE) with the smallest worthwhile change (SWC). Both the DJ and 10-5 RJT were reliable in determining RSI, with CV ≤ 10% and ICC ≥ 0.8. The TE was 0.09 and 0.08 for the DJ and 10-5 RJT, respectively. Both tests were unable to detect the SWC, rating them as 'marginal'; however, they were rated as 'good' in detecting moderate change in RSI. The Output Sports IMU is reliable in determining RSI for the DJ and 10-5 RJT; however, it is unable to detect the SWC. Future research must determine validity of the Output Sports IMU in measuring RSI.