Assessment of the reliability of vertical jump performance from an instrumented platform

Vertical jump performance is an integral component to success in many athletic endeavors. Measurement is typically accomplished with a slapstick-based device, which merely indicates the vertical jump height attained. However a recently created device calculates jump height from measurements collected as a person ascends, remains in the air, and lands on an instrumented platform. Before the platform can be used instead of the slapstick-based jump device, the reliability of its heights in relation to the latter device must first be ascertained. The purpose of this project is to assess the reliability of vertical heights measured from the instrumented platform to those concurrently obtained from the slapstick-based jump device. Subjects (n = 105) performed two separate jump trials. Preceded by a familiarization session, each trial consisted of a warm-up, followed by a series of vertical jumps performed with maximal effort. The instrumented device included a triangular-shaped platform and three load cells that measure forces associated with the vertical jump. Next to the instrumented platform was a device equipped with slapsticks separated in 1.27cm increments to provide simultaneous measurement of subject's performance. Thus with each jump, values derived from the instrumented platform were compared to those measured by slapsticks to assess the reliability of the former device. On-line data collection and software calculated subject's jump height from the instrumented platform based on their takeoff, hang time, and landing. Reliability assessed platform vertical jump height estimates from takeoff, hang time and landing to slapstick-based values. Prior to the assessment of reliability, data were examined with Bland-Altman plots for the detection of statistical outliers and heteroskedasticity. Intraclass correlation coefficients (ICC) were used to assess statistical reliability. With slapstick-based values as the criterion measure, ICC for jump height were as follows: takeoff= 0.90, hang time = 0.93 and landing = 0.67. Results suggest vertical jump height estimates from takeoff and hang time, but not landing, serve as reliable measures of performance assessed from the slapsticks. Apparently as subjects landed on the platform, impact forces reduced the reliability of height estimates derived from landing. In contrast, since subjects remained motionless at the start of jumps, this may have reduced the variability of the data and increased the reliability of measurements derived from takeoff on the platform. Future work should attempt to derive more reliable values estimated from landing, yet current results suggest the instrumented platform may be beneficial in the assessment of vertical jump performance.