Can Lateral Cyclic Reactive Jump Ability Be Reliably Measured Using an Inertial Measurement Unit?

Jump testing is widely used to assess lower-limb power, force absorption, and stretch-shortening cycle (SSC) function; however, lateral cyclic tests remain underexplored despite their relevance to change-of-direction performance. This study determined the intra- and inter-session reliability of a novel cyclic lateral leg power test using an inertial measurement unit (IMU). Seventeen female athletes completed three identical testing sessions separated by seven days. Participants performed 10 consecutive lateral bounds at distances of 1.0×, 1.25×, and 1.5× leg length on each limb. A foot-mounted inertial measurement unit (IMU) (Output Sports Ltd., Dublin, Ireland) quantified contact time (CT) and air time (AT), with the five shortest values for each variable analyzed. Reliability was assessed using percent change in the mean, coefficients of variation (CV), and intraclass correlation coefficients (ICC). Between-session changes were small (-7.9% to 6.6%), with no significant session effects for CT or AT. CVs ranged from 9.2% to 21.8%, with only CT at 1.0× leg length between Sessions 1 and 2 below 10%. ICCs ranged from 0.12 to 0.76, indicating poor-to-good relative reliability. Overall, the IMU-instrumented lateral cyclic test demonstrated largely unacceptable reliability, particularly at greater jump distances, indicating that further protocol refinement is required before implementation in clinical or performance settings.