Assessing Reactive Strength Measures in Jumping and Hopping Using the Optojump™ System

Abstract

The aim of this study was to assess the concurrent validity of the Optojump™ system (Microgate, Bolzano, Italy) versus a force platform in the estimation of temporal and reactive strength measures. In two separate investigations, twenty physically active males performed double-leg and single-leg drop jumps from a box height of 0.3 m and a 10 s vertical bilateral hopping test. Contact time, flight time and total time (the sum of contact and flight time) were concurrently assessed during single and double-leg drop jumps and during hopping. Jump height, the reactive strength index and the reactive strength ratio were also calculated from contact time and flight time. Despite intraclass correlation coefficients (ICCs) for all variables being close to 1 (ICC > 0.975), a significant overestimation was found in contact time (0.005 ± 0.002 s) and underestimations in flight time (0.005 ± 0.003 s), the reactive strength index (0.04 ± 0.02 m·s-1) and the reactive strength ratio (0.07 ± 0.04). Overestimations in contact time and underestimations in flight time were attributed to the physical design of the Optojump™ system as the transmitter and receiver units were positioned 0.003 m above the floor level. The Optojump™ demonstrated excellent overall temporal validity with no differences found between systems for total time. Coaches are advised to be consistent with the instrumentation used to assess athletes, however, in the case of comparison between reactive strength values collected with the Optojump™ and values collected with a force platform, regression equations are provided.

Interday Reliability and Usefulness of a Reactive Strength Index Derived From 2 Maximal Rebound Jump Tests

“…The Optojump TM consists of two parallel bars connected to a personal computer with one bar acting as a transmitter unit containing 96 light emitting diodes positioned 0.003 m above the ground and the other bar acting as a receiver unit. 22 When a participant performs a rebound jump within the parallel bar configuration the light is interrupted by the participant's foot during the jump, which triggers the timer in the unit and records with a precision of 1 ms. 22 The total time that the light is interrupted is a measure of contact time and the total time between interruptions is a measure of flight time. 22 This system has been reported as a valid measurement of RSI.…”

“…22 When a participant performs a rebound jump within the parallel bar configuration the light is interrupted by the participant's foot during the jump, which triggers the timer in the unit and records with a precision of 1 ms. 22 The total time that the light is interrupted is a measure of contact time and the total time between interruptions is a measure of flight time. 22 This system has been reported as a valid measurement of RSI. 22…”

Reliability of the OptoJump Next System for Measuring Temporal Values in Elite Racewalking

“…One useful feature of OptoJump Next when training on a treadmill is its "Biofeedback" functionality (15); this is where the software displays real-time measures of spatiotemporal variables, such as flight time in racewalking. Using the default LED setting of 0_0 is therefore crucial for obtaining accurate feedback; what is also essential is to consider other settings, in particular the minimum flight time setting.…”

The Use of an Optical Measurement System to Monitor Sports Performance

“…The current gold standard for measuring ground contact time (GCT) is the use of a force platform [ 6 ]. Both force platform and high speed camera have been used to capture GCT while sprinting [ 5 , 7 , 8 ].…”

“…Optical sensor devices may provide coaches and sport scientists with a more time efficient equivalent to the common lab based testing that is usually predicated on the use of high speed camera or force platform monitoring. In an effort to replicate and further investigate measurement validity, the current study utilized a similar design to Healy, Kenny & Harrison [ 6 ]. The aforementioned study aimed to assess the concurrent validity of the Optojump system in estimation of ground contact time and reactive strength measures when compared with a force platform.…”