A comparison of methods to examine double and single leg drop jump performance

The purpose of this study was to compare the use of both a force platform and Optojump photocell system (Microgate, Bolzano, Italy) to examine double leg and single leg drop jumps. Thirteen physically active individuals performed 5 double leg drop jumps and 5 single leg drop jumps from a height of 0.3 m. Ground contact time (CT), flight height (FH) and reactive strength index (RSI) were calculated concurrently for both jump types. Despite intraclass correlation coefficients for all variables being very close to 1, a significant systematic difference was consistently observed between both devices with the Optojump system overestimating CT and underestimating both FH and RSI for both jump types. Both devices demonstrated excellent test- retest reliability with all ICCs for CT, FH and RSI above 0.940.